Pilot’s Handbook of A

eronautical Know

ledge

FAA

-H-8083-25

PILOT’S HANDBOOK of

Aeronautical Knowledge

2003

U.S. DEPARTMENT OF TRANSPORTATIONFEDERAL AVIATION ADMINISTRATION

Flight Standards Service

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PREFACE

The Pilot’s Handbook of Aeronautical Knowledge provides basic knowledge that is essential for pilots. This hand-book introduces pilots to the broad spectrum of knowledge that will be needed as they progress in their pilot train-ing. Except for the Code of Federal Regulations pertinent to civil aviation, most of the knowledge areas applicableto pilot certification are presented. This handbook is useful to beginning pilots, as well as those pursuing moreadvanced pilot certificates.

Occasionally, the word “must” or similar language is used where the desired action is deemed critical. The use ofsuch language is not intended to add to, interpret, or relieve a duty imposed by Title 14 of the Code of FederalRegulations (14 CFR).

It is essential for persons using this handbook to also become familiar with and apply the pertinent parts of 14 CFRand the Aeronautical Information Manual (AIM). The AIM is available online at http://www.faa.gov/atpubs.

The current Flight Standards Service airman training and testing material and subject matter knowledge codes for allairman certificates and ratings can be obtained from the Flight Standards Service Web site at http://av-info.faa.gov.

This handbook supersedes Advisory Circular (AC) 61-23C, Pilot’s Handbook of Aeronautical Knowledge, dated1997.

This publication may be purchased from the Superintendent of Documents, U.S. Government Printing Office (GPO),Washington, DC 20402-9325, or from http://bookstore.gpo.gov. This handbook is also available for download fromthe Flight Standards Service Web site at http://av-info.faa.gov.

This handbook is published by the U.S. Department of Transportation, Federal Aviation Administration, AirmanTesting Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125. Comments regarding this hand-book should be sent in e-mail form to AFS630comments@faa.gov.

AC 00-2, Advisory Circular Checklist, transmits the current status of FAA advisory circulars and other flight information and publications. This checklist is available via the Internet athttp://www.faa.gov/aba/html_policies/ac00_2.html.

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Chapter 1—Aircraft StructureMajor Components ........................................1-1

Fuselage ....................................................1-2Wings........................................................1-3Empennage ...............................................1-4Landing Gear ............................................1-4The Powerplant.........................................1-5

Chapter 2—Principles of FlightStructure of the Atmosphere..........................2-1

Atmospheric Pressure...............................2-2Effects of Pressure on Density .................2-2Effect of Temperature on Density ............2-2Effect of Humidity on Density .................2-2

Newton’s Laws of Motion and Force............2-2Magnus Effect ...............................................2-3Bernoulli’s Principle of Pressure...................2-3Airfoil Design................................................2-4Low Pressure Above......................................2-5High Pressure Below.....................................2-6Pressure Distribution .....................................2-6

Chapter 3—Aerodynamics of FlightForces Acting on the Airplane.......................3-1

Thrust........................................................3-2Drag ..........................................................3-3Weight.......................................................3-5Lift ............................................................3-6

Wingtip Vortices ............................................3-6Ground Effect ................................................3-7Axes of an Airplane.......................................3-8Moments and Moment Arm ..........................3-9Design Characteristics ...................................3-9

Basic Concepts of Stability ....................3-10Static Stability ........................................3-10Dynamic Stability ...................................3-11Longitudinal Stability (Pitching) ............3-11Lateral Stability (Rolling) ......................3-14Vertical Stability (Yawing) .....................3-15Free Directional Oscillations(Dutch Roll)...........................................3-16Spiral Instability .....................................3-16

Aerodynamic Forces in Flight Maneuvers ..3-17Forces in Turns .......................................3-17Forces in Climbs.....................................3-19Forces in Descents..................................3-19

Stalls ............................................................3-20Basic Propeller Principles ...........................3-21

Torque and P Factor................................3-23Torque Reaction......................................3-23Corkscrew Effect ....................................3-24Gyroscopic Action ..................................3-24

Asymmetric Loading (P Factor).............3-25Load Factors ................................................3-26

Load Factors in Airplane Design............3-26Load Factors in Steep Turns...................3-27Load Factors and Stalling Speeds ..........3-28Load Factors and Flight Maneuvers.......3-29VG Diagram ...........................................3-30

Weight and Balance.....................................3-31Effects of Weight onFlight Performance ................................3-32Effect of Weight on Airplane Structure..3-32Effects of Weight on Stability andControllability........................................3-33Effect of Load Distribution ....................3-33

High Speed Flight........................................3-35Supersonic vs. Subsonic Flow................3-35Speed Ranges..........................................3-35Mach Number vs. Airspeed....................3-36Boundary Layer ......................................3-36Shock Waves...........................................3-37Sweepback ..............................................3-38Mach Buffet Boundaries.........................3-39Flight Controls........................................3-40

Chapter 4—Flight ControlsPrimary Flight Controls.................................4-1

Ailerons ....................................................4-1Adverse Yaw.............................................4-2

Differential Ailerons .............................4-2Frise-Type Ailerons ..............................4-2Coupled Ailerons and Rudder ..............4-3

Elevator.....................................................4-3T-Tail.........................................................4-3Stabilator...................................................4-4Canard.......................................................4-5Rudder ......................................................4-5V-Tail ........................................................4-6

Secondary Flight Controls.............................4-6Flaps..........................................................4-6Leading Edge Devices..............................4-7Spoilers .....................................................4-7Trim Systems............................................4-8

Trim Tabs..............................................4-8Balance Tabs.........................................4-8Antiservo Tabs......................................4-8Ground Adjustable Tabs .......................4-9Adjustable Stabilizer ............................4-9

Chapter 5—Aircraft SystemsPowerplant .....................................................5-1

Reciprocating Engines..............................5-1Propeller....................................................5-2

CONTENTS

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Fixed-Pitch Propeller............................5-3Adjustable-Pitch Propeller....................5-4

Induction Systems ....................................5-5Carburetor Systems ..............................5-5

Mixture Control ................................5-5Carburetor Icing................................5-6Carburetor Heat ................................5-7Carburetor Air Temperature Gauge..5-8Outside Air Temperature Gauge.......5-8

Fuel Injection Systems .........................5-8Superchargers and Turbosuperchargers....5-9

Superchargers .......................................5-9Turbosuperchargers ............................5-10

System Operation ...........................5-10High Altitude Performance.............5-11

Ignition System.......................................5-11Combustion.............................................5-12Fuel Systems...........................................5-13

Fuel Pumps .........................................5-14Fuel Primer .........................................5-14Fuel Tanks...........................................5-14Fuel Gauges ........................................5-14Fuel Selectors .....................................5-14Fuel Strainers, Sumps, and Drains .....5-14Fuel Grades.........................................5-15

Fuel Contamination ........................5-15Refueling Procedures......................5-16

Starting System.......................................5-16Oil Systems.............................................5-16Engine Cooling Systems ........................5-18Exhaust Systems.....................................5-19Electrical System....................................5-19Hydraulic Systems..................................5-22Landing Gear ..........................................5-22

Tricycle Landing Gear Airplanes .......5-22Tailwheel Landing Gear Airplanes.....5-23Fixed and Retractable Landing Gear..5-23Brakes .................................................5-23

Autopilot.................................................5-23Pressurized Airplanes ..................................5-24

Oxygen Systems .....................................5-26Masks..................................................5-27Diluter Demand Oxygen Systems ......5-27Pressure Demand Oxygen Systems....5-27Continuous Flow Oxygen System......5-27Servicing of Oxygen Systems ............5-28

Ice Control Systems................................5-28Airfoil Ice Control ..............................5-28Windscreen Ice Control ......................5-29Propeller Ice Control ..........................5-29Other Ice Control Systems .................5-29

Turbine Engines...........................................5-29Types of Turbine Engines.......................5-30

Turbojet...............................................5-30Turboprop ...........................................5-30Turbofan .............................................5-30Turboshaft...........................................5-31Performance Comparison ...................5-31

Turbine Engine Instruments ...................5-31Engine Pressure Ratio ........................5-32Exhaust Gas Temperature...................5-32Torquemeter........................................5-32N1 Indicator........................................5-32N2 Indicator........................................5-32

Turbine Engine Operational Considerations .......................................5-32

Engine Temperature Limitations ........5-32Thrust Variations ................................5-32Foreign Object Damage......................5-32Turbine Engine Hot/Hung Start .........5-33Compressor Stalls...............................5-33Flameout .............................................5-33

Chapter 6—Flight InstrumentsPitot-Static Flight Instruments.......................6-1

Impact Pressure Chamber and Lines........6-1Static Pressure Chamber and Lines..........6-1Altimeter...................................................6-2

Principle of Operation ..........................6-2Effect of Nonstandard Pressure andTemperature .........................................6-2Setting the Altimeter.............................6-3Altimeter Operation..............................6-4Types of Altitude ..................................6-4

Indicated Altitude .............................6-4True Altitude.....................................6-4Absolute Altitude..............................6-4Pressure Altitude...............................6-4Density Altitude................................6-5

Vertical Speed Indicator ...........................6-5Principle of Operation ..........................6-5

Airspeed Indicator ....................................6-6Indicated Airspeed ................................6-6Calibrated Airspeed ..............................6-6True Airspeed .......................................6-6Groundspeed.........................................6-6Airspeed Indicator Markings................6-6Other Airspeed Limitations ..................6-7

Blockage of the Pitot-Static System.........6-8Blocked Pitot System ...........................6-8Blocked Static System..........................6-8

Gyroscopic Flight Instruments ......................6-9Gyroscopic Principles...............................6-9

Rigidity in Space ..................................6-9Precession .............................................6-9

Sources of Power....................................6-10Turn Indicators .......................................6-10

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Turn-and-Slip Indicator ......................6-11Turn Coordinator ................................6-11

Inclinometer ............................................6-11The Attitude Indicator ............................6-12Heading Indicator ...................................6-12

Magnetic Compass ......................................6-14Compass Errors ......................................6-15

Variation..............................................6-15Compass Deviation.............................6-16Magnetic Dip ......................................6-16Using the Magnetic Compass.............6-16

Acceleration/Deceleration Errors ...6-16Turning Errors ................................6-16

Vertical Card Compass ...........................6-17Outside Air Temperature Gauge..................6-17

Chapter 7—Flight Manuals and OtherDocumentsAirplane Flight Manuals................................7-1

Preliminary Pages.....................................7-1General (Section 1)...................................7-2Limitations (Section 2).............................7-2

Airspeed................................................7-2Powerplant ............................................7-2Weight and Loading Distribution .........7-2Flight Limits .........................................7-3Placards.................................................7-3

Emergency Procedures (Section 3) ..........7-3Normal Procedures (Section 4) ................7-3Performance (Section 5) ...........................7-3Weight and Balance/Equipment List(Section 6) ...............................................7-3Systems Description (Section 7) ..............7-4Handling, Service, and Maintenance(Section 8) ...............................................7-4Supplements (Section 9)...........................7-4Safety Tips (Section 10) ...........................7-5

Aircraft Documents .......................................7-5Certificate of Aircraft Registration...........7-5Airworthiness Certificate..........................7-6

Aircraft Maintenance.....................................7-7Aircraft Inspections ..................................7-7

Annual Inspection.................................7-7100-Hour Inspection.............................7-7Other Inspection Programs...................7-8Altimeter System Inspection ................7-8Transponder Inspection ........................7-8Preflight Inspections.............................7-8Minimum Equipment Lists(MEL) and Operationswith Inoperative Equipment ................7-8

Preventive Maintenance ...........................7-9Repairs and Alterations ............................7-9Special Flight Permits ..............................7-9

Airworthiness Directives ........................7-10Aircraft Owner/OperatorResponsibilities......................................7-11

Chapter 8—Weight and BalanceWeight Control ..............................................8-1

Effects of Weight ......................................8-1Weight Changes........................................8-2

Balance, Stability, and Center of Gravity......8-2Effects of Adverse Balance ......................8-2Management of Weight andBalance Control .......................................8-3Terms and Definitions ..............................8-3Basic Principles of Weight andBalance Computations.............................8-4Weight and Balance Restrictions..............8-6

Determining Loaded Weight and Centerof Gravity......................................................8-6

Computational Method.............................8-6Graph Method...........................................8-6Table Method............................................8-8Computations with a Negative Arm.........8-8Computations with Zero Fuel Weight ......8-9Shifting, Adding,and Removing Weight .............................8-9

Weight Shifting.....................................8-9Weight Addition or Removal..............8-10

Chapter 9—Aircraft PerformanceImportance of Performance Data ..................9-1Structure of the Atmosphere..........................9-1

Atmospheric Pressure...............................9-1Pressure Altitude.......................................9-2Density Altitude........................................9-3

Effects of Pressure on Density .............9-4Effects of Temperature on Density.......9-4Effect of Humidity (Moisture)on Density............................................9-4

Performance...................................................9-4Straight-and-Level Flight .........................9-5Climb Performance...................................9-6Range Performance ..................................9-8Ground Effect .........................................9-10Region of Reversed Command ..............9-12Runway Surface and Gradient................9-13Water on the Runway and DynamicHydroplaning .........................................9-14

Takeoff and Landing Performance ..............9-15Takeoff Performance ..............................9-15Landing Performance .............................9-17

Performance Speeds ....................................9-18Performance Charts .....................................9-19

Interpolation............................................9-20Density Altitude Charts ..........................9-20Takeoff Charts ........................................9-22Climb and Cruise Charts ........................9-23

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Crosswind and HeadwindComponent Chart...................................9-28Landing Charts .......................................9-29Stall Speed Performance Charts .............9-30

Transport Category AirplanePerformance................................................9-31

Major Differences in TransportCategory versus Non-TransportCategory Performance Requirements....9-31Performance Requirements ....................9-31Runway Requirements............................9-32Balanced Field Length............................9-32Climb Requirements...............................9-34

First Segment......................................9-35Second Segment .................................9-35Third or Acceleration Segment ..........9-35Forth or Final Segment.......................9-35Second Segment Climb Limitations...9-35

Air Carrier Obstacle ClearanceRequirements .........................................9-36Summary of Takeoff Requirements........9-36Landing Performance .............................9-37

Planning the Landing..........................9-37Landing Requirements........................9-37Approach Climb Requirements ..........9-37Landing Runway Required.................9-37Summary of LandingRequirements .....................................9-38

Examples of Performance Charts ................9-39

Chapter 10—Weather TheoryNature of the Atmosphere ...........................10-1

Oxygen and the Human Body ................10-2Significance of Atmospheric Pressure....10-3

Measurement of AtmosphericPressure..............................................10-3Effect of Altitude on AtmosphericPressure..............................................10-4Effect of Altitude on Flight ................10-4Effect of Differences in Air Density ..10-5Wind ...................................................10-5

The Cause of Atmosphere Circulation ........10-5Wind Patterns .........................................10-6Convective Currents ...............................10-7Effect of Obstructions on Wind..............10-8Low-Level Wind Shear ..........................10-9Wind and Pressure Representationon Surface Weather Maps....................10-11

Atmospheric Stability................................10-12Inversion ...............................................10-13Moisture and Temperature....................10-13Relative Humidity ................................10-13Temperature/Dewpoint Relationship....10-13Methods By Which Air Reachesthe Saturation Point .............................10-14

Dew and Frost ......................................10-14Fog........................................................10-14Clouds...................................................10-15Ceiling ..................................................10-17Visibility ...............................................10-18Precipitation..........................................10-18

Air Masses .................................................10-18Fronts .........................................................10-18

Warm Front...........................................10-19Flight Toward an ApproachingWarm Front......................................10-20

Cold Front.............................................10-20Fast-Moving Cold Front...................10-21Flight Toward an ApproachingCold Front........................................10-21Comparison of Cold andWarm Fronts ....................................10-21

Wind Shifts ...........................................10-21Stationary Front ....................................10-22Occluded Front .....................................10-22

Chapter 11—Weather Reports, Forecasts,and ChartsObservations ................................................11-1

Surface Aviation WeatherObservations .........................................11-1

Upper Air Observations ..........................11-1Radar Observations.................................11-2

Service Outlets.............................................11-2FAA Flight Service Station.....................11-2Transcribed Information BriefingService (TIBS).......................................11-2Direct User Access TerminalService (DUATS)...................................11-2En Route Flight Advisory Service..........11-2Hazardous In-Flight WeatherAdvisory (HIWAS) ................................11-3Transcribed Weather Broadcast(TWEB) .................................................11-3

Weather Briefings ........................................11-3Standard Briefing....................................11-3Abbreviated Briefing ..............................11-4Outlook Briefing.....................................11-4

Aviation Weather Reports............................11-4Aviation Routine Weather Report(METAR) ...............................................11-4Pilot Weather Reports (PIREPs).............11-7Radar Weather Reports (SD) ..................11-8

Aviation Forecasts .......................................11-9Terminal Aerodrome Forecasts...............11-9Area Forecasts ......................................11-10In-Flight Weather Advisories................11-12

Airman’s MeteorologicalInformation (AIRMET) ...................11-12

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Significant MeteorologicalInformation (SIGMET)....................11-12Convective SignificantMeteorological Information(WST) ..............................................11-12

Winds and Temperature AloftForecast (FD).......................................11-13

Weather Charts...........................................11-14Surface Analysis Chart .........................11-14Weather Depiction Chart ......................11-15Radar Summary Chart ..........................11-16Significant Weather PrognosticCharts ...................................................11-18

Chapter 12—Airport OperationsTypes of Airports .........................................12-1

Controlled Airport ..................................12-1Uncontrolled Airport ..............................12-1

Sources for Airport Data .............................12-1Aeronautical Charts ................................12-1Airport/Facility Directory.......................12-1Notices to Airmen...................................12-3

Airport Markings and Signs ........................12-3Runway Markings ..................................12-3Taxiway Markings ..................................12-3Other Markings.......................................12-3Airport Signs ..........................................12-3

Airport Lighting...........................................12-5Airport Beacon .......................................12-5Approach Light Systems ........................12-6Visual Glideslope Indicators ..................12-6

Visual Approach Slope Indicator........12-6Other Glidepath Systems....................12-6

Runway Lighting ....................................12-6Runway End Identifier Lights ............12-6Runway Edge Lights ..........................12-7In-Runway Lighting ...........................12-7

Control of Airport Lighting ....................12-7Taxiway Lights .......................................12-8Obstruction Lights ..................................12-8

Wind Direction Indicators ...........................12-8Radio Communications ...............................12-8

Radio License .........................................12-8Radio Equipment ....................................12-8Lost Communication Procedures ...........12-9

Air Traffic Control Services ......................12-10Primary Radar.......................................12-10Air Traffic Control RadarBeacon System ....................................12-11Transponder ..........................................12-11Radar Traffic Information Service........12-11

Wake Turbulence .......................................12-12Vortex Generation.................................12-13Vortex Strength .....................................12-13

Vortex Behavior....................................12-13Vortex Avoidance Procedures...............12-13

Collision Avoidance...................................12-14Clearing Procedures..............................12-14Runway Incursion Avoidance...............12-14

Chapter 13—AirspaceControlled Airspace .....................................13-1

Class A Airspace.....................................13-1Class B Airspace.....................................13-1Class C Airspace.....................................13-1Class D Airspace ....................................13-3Class E Airspace.....................................13-3

Uncontrolled Airspace .................................13-3Class G Airspace ....................................13-3

Special Use Airspace ...................................13-3Prohibited Areas .....................................13-3Restricted Areas......................................13-3Warning Areas ........................................13-4Military Operation Areas........................13-4Alert Areas..............................................13-4Controlled Firing Areas ..........................13-4

Other Airspace Areas...................................13-4Airport Advisory Areas ..........................13-4Military Training Routes ........................13-4Temporary Flight Restrictions................13-4Parachute Jump Areas ............................13-4Published VFR Routes ...........................13-4Terminal Radar Service Areas................13-5National Security Areas..........................13-5

Chapter 14—NavigationAeronautical Charts .....................................14-1

Sectional Charts......................................14-1Visual Flight Rule Terminal AreaCharts.....................................................14-1World Aeronautical Charts .....................14-1

Latitude and Longitude (Meridians andParallels) .....................................................14-2

Time Zones .............................................14-2Measurement of Direction......................14-3Variation..................................................14-4Deviation ................................................14-5

Effect of Wind .............................................14-6Basic Calculations .......................................14-8

Converting Minutes to EquivalentHours .....................................................14-8Converting Knots to Miles Per Hour .....14-8Fuel Consumption ..................................14-8Flight Computers ....................................14-8Plotter......................................................14-8

Pilotage ......................................................14-10

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Dead Reckoning ........................................14-10The Wind Triangle or VectorAnalysis ...............................................14-10

Flight Planning ..........................................14-13Assembling Necessary Material ...........14-13Weather Check......................................14-13Use of the Airport/Facility Directory ...14-13Airplane Flight Manual or Pilot’sOperating Handbook ..........................14-13

Charting the Course...................................14-14Steps in Charting the Course................14-14

Filing a VFR Flight Plan ...........................14-16Radio Navigation.......................................14-17

Very High Frequency (VHF)Omnidirectional Range (VOR) ...........14-18

Using the VOR .................................14-19Tracking with VOR ..........................14-20Tips On Using the VOR ...................14-21

Distance Measuring Equipment ..........14-21VOR/DME RNAV................................14-21Automatic Direction Finder ................14-22Loran-C Navigation..............................14-24Global Position System .......................14-26

Lost Procedures .........................................14-27Flight Diversion.........................................14-27

Chapter 15—Aeromedical FactorsObtaining a Medical Certificate ..................15-1Environmental and Health FactorsAffecting Pilot Performance.......................15-2

Hypoxia ..................................................15-2Hypoxic Hypoxia................................15-2Hypemic Hypoxia...............................15-2Stagnant Hypoxia ...............................15-2Histotoxic Hypoxia.............................15-2Symptoms of Hypoxia........................15-2

Hyperventilation .....................................15-3Middle Ear and Sinus Problems.............15-3

Spatial Disorientation and Illusions .......15-4Motion Sickness .....................................15-6Carbon Monoxide Poisoning..................15-6Stress.......................................................15-6Fatigue ....................................................15-7Dehydration and Heatstroke...................15-7Alcohol ...................................................15-8Drugs ......................................................15-8Scuba Diving ..........................................15-9

Vision in Flight ............................................15-9Empty-Field Myopia ............................15-10Night Vision..........................................15-10Night Vision Illusions...........................15-11

Autokinesis .......................................15-11False Horizon....................................15-11Night Landing Illusions....................15-12

Chapter 16—Aeronautical Decision MakingOrigins of ADM Training............................16-2The Decision-Making Process.....................16-2

Defining the Problem .............................16-2Choosing a Course of Action .................16-3Implementing the Decision andEvaluating the Outcome ........................16-4

Risk Management........................................16-4Assessing Risk........................................16-5

Factors Affecting Decision Making ............16-5Pilot Self-Assessment.............................16-5Recognizing Hazardous Attitudes ..........16-6Stress Management.................................16-6Use of Resources ....................................16-7

Internal Resources ..............................16-7External Resources .............................16-8

Workload Management...........................16-8Situational Awareness.............................16-8Obstacles to Maintaining SituationalAwareness ..............................................16-9

Operational Pitfalls ......................................16-9

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According to the current Title 14 of the Code of FederalRegulations (14 CFR) part 1, Definitions andAbbreviations, an aircraft is a device that is used, orintended to be used, for flight. Categories of aircraft forcertification of airmen include airplane, rotorcraft,lighter-than-air, powered-lift, and glider. Part 1 alsodefines airplane as an engine-driven, fixed-wing aircraft heavier than air that is supported in flight by thedynamic reaction of air against its wings. This chapter

provides a brief introduction to the airplane and itsmajor components.

MAJOR COMPONENTSAlthough airplanes are designed for a variety of pur-poses, most of them have the same major components.The overall characteristics are largely determined bythe original design objectives. Most airplane structuresinclude a fuselage, wings, an empennage, landing gear,and a powerplant. [Figure 1-1]

Figure 1-1. Airplane components.

Empennage

Wing

Fuselage

PowerplantLanding Gear

Aircraft—A device that is used for flight in the air.

Airplane—An engine-driven, fixed-wing aircraft heavier than air that issupported in flight by the dynamic reaction of air against its wings.

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FUSELAGEThe fuselage includes the cabin and/or cockpit, whichcontains seats for the occupants and the controls forthe airplane. In addition, the fuselage may alsoprovide room for cargo and attachment points for theother major airplane components. Some aircraft uti-lize an open truss structure. The truss-type fuselage isconstructed of steel or aluminum tubing. Strength andrigidity is achieved by welding the tubing togetherinto a series of triangular shapes, called trusses.[Figure 1-2]

Construction of the Warren truss features longerons,as well as diagonal and vertical web members. Toreduce weight, small airplanes generally utilize aluminum alloy tubing, which may be riveted orbolted into one piece with cross-bracing members.

As technology progressed, aircraft designers began toenclose the truss members to streamline the airplaneand improve performance. This was originally accom-plished with cloth fabric, which eventually gave way tolightweight metals such as aluminum. In some cases,the outside skin can support all or a major portion ofthe flight loads. Most modern aircraft use a form of thisstressed skin structure known as monocoque or semi-monocoque construction.

The monocoque design uses stressed skin to supportalmost all imposed loads. This structure can be verystrong but cannot tolerate dents or deformation of thesurface. This characteristic is easily demonstrated by athin aluminum beverage can. You can exert considerableforce to the ends of the can without causing any damage.

However, if the side of the can is dented only slightly,the can will collapse easily. The true monocoque con-struction mainly consists of the skin, formers, andbulkheads. The formers and bulkheads provide shapefor the fuselage. [Figure 1-3]

Since no bracing members are present, the skin must bestrong enough to keep the fuselage rigid. Thus, a significant problem involved in monocoque construc-tion is maintaining enough strength while keeping theweight within allowable limits. Due to the limitations ofthe monocoque design, a semi-monocoque structure isused on many of today’s aircraft.

The semi-monocoque system uses a substructure towhich the airplane’s skin is attached. The substructure,which consists of bulkheads and/or formers of varioussizes and stringers, reinforces the stressed skin by taking some of the bending stress from the fuselage.The main section of the fuselage also includes wingattachment points and a firewall. [Figure 1-4]

Longeron

Diagonal Web Members

VerticalWeb

Members

Figure 1-2.The Warren truss.

Truss—A fuselage design made up of supporting structural membersthat resist deformation by applied loads.

Monocoque—A shell-like fuselage design in which the stressed outerskin is used to support the majority of imposed stresses. Monocoquefuselage design may include bulkheads but not stringers.

Skin Former

Bulkhead

Figure 1-3. Monocoque fuselage design.

Bulkheadsand/or

Formers

Stressed Skin

Wing AttachmentPoints

Firewall

Stringers

Figure 1-4. Semi-monocoque construction.

Semi-Monocoque—A fuselage design that includes a substructure ofbulkheads and/or formers, along with stringers, to support flight loadsand stresses imposed on the fuselage.

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On single-engine airplanes, the engine is usuallyattached to the front of the fuselage. There is a fireproofpartition between the rear of the engine and the cockpitor cabin to protect the pilot and passengers from accidental engine fires. This partition is called a firewall and is usually made of heat-resistant materialsuch as stainless steel.

WINGSThe wings are airfoils attached to each side of the fuselage and are the main lifting surfaces that supportthe airplane in flight. There are numerous wingdesigns, sizes, and shapes used by the various manu-facturers. Each fulfills a certain need with respect tothe expected performance for the particular airplane.How the wing produces lift is explained in subsequentchapters.

Wings may be attached at the top, middle, or lower por-tion of the fuselage. These designs are referred to ashigh-, mid-, and low-wing, respectively. The number ofwings can also vary. Airplanes with a single set ofwings are referred to as monoplanes, while those withtwo sets are called biplanes. [Figure 1-5]

Many high-wing airplanes have external braces, orwing struts, which transmit the flight and landing loads

through the struts to the main fuselage structure. Sincethe wing struts are usually attached approximatelyhalfway out on the wing, this type of wing structure iscalled semi-cantilever. A few high-wing and most low-wing airplanes have a full cantilever wingdesigned to carry the loads without external struts.

The principal structural parts of the wing are spars,ribs, and stringers. [Figure 1-6] These are reinforced by

Airfoil—An airfoil is any surface, such as a wing, propeller, rudder, oreven a trim tab, which provides aerodynamic force when it interactswith a moving stream of air.

Monoplane—An airplane that has only one main lifting surface orwing, usually divided into two parts by the fuselage.

Biplane—An airplane that has two main airfoil surfaces or wings oneach side of the fuselage, one placed above the other.

Figure 1-5. Monoplane and biplane.

Spar

Skin

Wing Flap

Aileron

Stringers

WingTip

Ribs

Spar

Fuel Tank

Figure 1-6. Wing components.

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trusses, I-beams, tubing, or other devices, including theskin. The wing ribs determine the shape and thicknessof the wing (airfoil). In most modern airplanes, the fueltanks either are an integral part of the wing’s structure,or consist of flexible containers mounted inside of thewing.

Attached to the rear, or trailing, edges of the wings aretwo types of control surfaces referred to as ailerons andflaps. Ailerons extend from about the midpoint of eachwing outward toward the tip and move in oppositedirections to create aerodynamic forces that cause theairplane to roll. Flaps extend outward from the fuselage to near the midpoint of each wing. The flapsare normally flush with the wing’s surface during cruising flight. When extended, the flaps move simul-taneously downward to increase the lifting force of thewing for takeoffs and landings.

EMPENNAGEThe correct name for the tail section of an airplane isempennage. The empennage includes the entire tailgroup, consisting of fixed surfaces such as the verticalstabilizer and the horizontal stabilizer. The movable sur-faces include the rudder, the elevator, and one or moretrim tabs. [Figure 1-7]

A second type of empennage design does not requirean elevator. Instead, it incorporates a one-piece hori-zontal stabilizer that pivots from a central hinge point.This type of design is called a stabilator, and is movedusing the control wheel, just as you would the eleva-tor. For example, when you pull back on the controlwheel, the stabilator pivots so the trailing edge movesup. This increases the aerodynamic tail load andcauses the nose of the airplane to move up. Stabilatorshave an antiservo tab extending across their trailingedge. [Figure 1-8]

The antiservo tab moves in the same direction as thetrailing edge of the stabilator. The antiservo tab alsofunctions as a trim tab to relieve control pressures andhelps maintain the stabilator in the desired position.

The rudder is attached to the back of the vertical stabi-lizer. During flight, it is used to move the airplane’snose left and right. The rudder is used in combinationwith the ailerons for turns during flight. The elevator,which is attached to the back of the horizontal stabi-lizer, is used to move the nose of the airplane up anddown during flight.

Trim tabs are small, movable portions of the trailingedge of the control surface. These movable trim tabs,which are controlled from the cockpit, reduce controlpressures. Trim tabs may be installed on the ailerons,the rudder, and/or the elevator.

LANDING GEARThe landing gear is the principle support of the airplanewhen parked, taxiing, taking off, or when landing. The

VerticalStabilizer

HorizontalStabilizer

Rudder

Trim Tabs

Elevator

Figure 1-7. Empennage components.

Empennage—The section of the airplane that consists of the verticalstabilizer, the horizontal stabilizer, and the associated control surfaces.

Stabilator

AntiservoTab

Pivot Point

Figure 1-8. Stabilator components.

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most common type of landing gear consists of wheels,but airplanes can also be equipped with floats for wateroperations, or skis for landing on snow. [Figure 1-9]

The landing gear consists of three wheels—two mainwheels and a third wheel positioned either at the front orrear of the airplane. Landing gear employing a rear-mounted wheel is called conventional landing gear.Airplanes with conventional landing gear are sometimesreferred to as tailwheel airplanes. When the third wheel islocated on the nose, it is called a nosewheel, and thedesign is referred to as a tricycle gear. A steerable nose-wheel or tailwheel permits the airplane to be controlledthroughout all operations while on the ground.

THE POWERPLANTThe powerplant usually includes both the engine andthe propeller. The primary function of the engine is toprovide the power to turn the propeller. It also gener-ates electrical power, provides a vacuum source forsome flight instruments, and in most single-engine

airplanes, provides a source of heat for the pilot andpassengers. The engine is covered by a cowling, or inthe case of some airplanes, surrounded by a nacelle.The purpose of the cowling or nacelle is to stream-line the flow of air around the engine and to help coolthe engine by ducting air around the cylinders. Thepropeller, mounted on the front of the engine, trans-lates the rotating force of the engine into a forward-acting force called thrust that helps move the airplanethrough the air. [Figure 1-10]

Engine

Cowling

Propeller

Firewall

Figure 1-10. Engine compartment.

Figure 1-9. Landing gear.

Nacelle—A streamlined enclosure on an aircraft in which an engine ismounted. On multiengine propeller-driven airplanes, the nacelle is normally mounted on the leading edge of the wing.

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This chapter discusses the fundamental physical lawsgoverning the forces acting on an airplane in flight, andwhat effect these natural laws and forces have on theperformance characteristics of airplanes. Tocompetently control the airplane, the pilot mustunderstand the principles involved and learn to utilizeor counteract these natural forces.

Modern general aviation airplanes have what maybe considered high performance characteristics.Therefore, it is increasingly necessary that pilotsappreciate and understand the principles upon whichthe art of flying is based.

STRUCTURE OF THE ATMOSPHEREThe atmosphere in which flight is conducted is anenvelope of air that surrounds the earth and restsupon its surface. It is as much a part of the earth asthe seas or the land. However, air differs from landand water inasmuch as it is a mixture of gases. It hasmass, weight, and indefinite shape.

Air, like any other fluid, is able to flow and change itsshape when subjected to even minute pressures becauseof the lack of strong molecular cohesion. For example,gas will completely fill any container into which it isplaced, expanding or contracting to adjust its shape tothe limits of the container.

The atmosphere is composed of 78 percent nitrogen, 21percent oxygen, and 1 percent other gases, such asargon or helium. As some of these elements are heavierthan others, there is a natural tendency of these heavierelements, such as oxygen, to settle to the surface of theearth, while the lighter elements are lifted up to theregion of higher altitude. This explains why most of theoxygen is contained below 35,000 feet altitude.

Because air has mass and weight, it is a body, and as abody, it reacts to the scientific laws of bodies in thesame manner as other gaseous bodies. This body of airresting upon the surface of the earth has weight and atsea level develops an average pressure of 14.7 poundson each square inch of surface, or 29.92 inches of

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mercury—but as its thickness is limited, the higherthe altitude, the less air there is above. For thisreason, the weight of the atmosphere at 18,000 feetis only one-half what it is at sea level. [Figure 2-1]

ATMOSPHERIC PRESSUREThough there are various kinds of pressure, thisdiscussion is mainly concerned with atmosphericpressure. It is one of the basic factors in weatherchanges, helps to lift the airplane, and actuates someof the important flight instruments in the airplane.These instruments are the altimeter, the airspeedindicator, the rate-of-climb indicator, and themanifold pressure gauge.

Though air is very light, it has mass and is affectedby the attraction of gravity. Therefore, like any othersubstance, it has weight, and because of its weight, ithas force. Since it is a fluid substance, this force isexerted equally in all directions, and its effect onbodies within the air is called pressure. Understandard conditions at sea level, the average pressureexerted on the human body by the weight of theatmosphere around it is approximately 14.7 lb./in.The density of air has significant effects on theairplane’s capability. As air becomes less dense, itreduces (1) power because the engine takes in lessair, (2) thrust because the propeller is less efficient inthin air, and (3) lift because the thin air exerts lessforce on the airfoils.

EFFECTS OF PRESSURE ON DENSITYSince air is a gas, it can be compressed or expanded.When air is compressed, a greater amount of air can

occupy a given volume. Conversely, when pressureon a given volume of air is decreased, the airexpands and occupies a greater space. That is, theoriginal column of air at a lower pressure contains asmaller mass of air. In other words, the density isdecreased. In fact, density is directly proportional topressure. If the pressure is doubled, the density isdoubled, and if the pressure is lowered, so is thedensity. This statement is true, only at aconstant temperature.

EFFECT OF TEMPERATURE ON DENSITYThe effect of increasing the temperature of asubstance is to decrease its density. Conversely,decreasing the temperature has the effect ofincreasing the density. Thus, the density of air variesinversely as the absolute temperature varies. Thisstatement is true, only at a constant pressure.

In the atmosphere, both temperature and pressuredecrease with altitude, and have conflicting effectsupon density. However, the fairly rapid drop inpressure as altitude is increased usually has thedominating effect. Hence, density can be expected todecrease with altitude.

EFFECT OF HUMIDITY ON DENSITYThe preceding paragraphs have assumed that the airwas perfectly dry. In reality, it is never completelydry. The small amount of water vapor suspended inthe atmosphere may be almost negligible undercertain conditions, but in other conditions humiditymay become an important factor in the performanceof an airplane. Water vapor is lighter than air;consequently, moist air is lighter than dry air. It islightest or least dense when, in a given set ofconditions, it contains the maximum amount ofwater vapor. The higher the temperature, the greateramount of water vapor the air can hold. Whencomparing two separate air masses, the first warmand moist (both qualities tending to lighten the air)and the second cold and dry (both qualities making itheavier), the first necessarily must be less dense thanthe second. Pressure, temperature, and humidityhave a great influence on airplane performance,because of their effect upon density.

NEWTON’S LAWS OF MOTION ANDFORCEIn the 17th century, a philosopher andmathematician, Sir Isaac Newton, propounded threebasic laws of motion. It is certain that he did not havethe airplane in mind when he did so, but almosteverything known about motion goes back to histhree simple laws. These laws, named after Newton,are as follows:

Newton’s first law states, in part, that: A body at resttends to remain at rest, and a body in motion tends to

29.92 30

25

20

15

10

5

0

Inch

es o

f Mer

cury

AtmosphericPressure

StandardSea LevelPressure

Figure 2-1. Standard sea level pressure.

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remain moving at the same speed and in thesame direction.

This simply means that, in nature, nothing starts orstops moving until some outside force causes it to doso. An airplane at rest on the ramp will remain at restunless a force strong enough to overcome its inertia isapplied. Once it is moving, however, its inertia keeps itmoving, subject to the various other forces acting on it.These forces may add to its motion, slow it down, orchange its direction.

Newton’s second law implies that: When a body isacted upon by a constant force, its resultingacceleration is inversely proportional to the mass of thebody and is directly proportional to the applied force.

What is being dealt with here are the factors involvedin overcoming Newton’s First Law of Inertia. It coversboth changes in direction and speed, including startingup from rest (positive acceleration) and coming to astop (negative acceleration, or deceleration).

Newton’s third law states that: Whenever one bodyexerts a force on another, the second body alwaysexerts on the first, a force that is equal in magnitude butopposite in direction.

The recoil of a gun as it is fired is a graphic example ofNewton’s third law. The champion swimmer whopushes against the side of the pool during theturnaround, or the infant learning to walk—both wouldfail but for the phenomena expressed in this law. In anairplane, the propeller moves and pushes back the air;consequently, the air pushes the propeller (and thus theairplane) in the opposite direction—forward. In a jetairplane, the engine pushes a blast of hot gasesbackward; the force of equal and opposite reactionpushes against the engine and forces the airplaneforward. The movement of all vehicles is a graphicillustration of Newton’s third law.

MAGNUS EFFECTThe explanation of lift can best be explained by lookingat a cylinder rotating in an airstream. The local velocitynear the cylinder is composed of the airstream velocityand the cylinder’s rotational velocity, which decreaseswith distance from the cylinder. On a cylinder, which isrotating in such a way that the top surface area is rotatingin the same direction as the airflow, the local velocity atthe surface is high on top and low on the bottom.

As shown in figure 2-2, at point “A,” a stagnation pointexists where the airstream line that impinges on thesurface splits; some air goes over and some under.Another stagnation point exists at “B,” where the two

airstreams rejoin and resume at identical velocities. Wenow have upwash ahead of the rotating cylinder anddownwash at the rear.

The difference in surface velocity accounts for a differ-ence in pressure, with the pressure being lower on thetop than the bottom. This low pressure area produces anupward force known as the “Magnus Effect.” Thismechanically induced circulation illustrates therelationship between circulation and lift.

An airfoil with a positive angle of attack develops aircirculation as its sharp trailing edge forces the rearstagnation point to be aft of the trailing edge, while thefront stagnation point is below the leading edge.[Figure 2-3]

BERNOULLI’S PRINCIPLE OFPRESSUREA half century after Sir Newton presented his laws,Mr. Daniel Bernoulli, a Swiss mathematician,explained how the pressure of a moving fluid (liquidor gas) varies with its speed of motion. Specifically,

B A

Increased Local Velocity(Decreased pressure)

Decreased Local Velocity

Downwash Upwash

Figure 2-2. Magnus Effect is a lifting force produced when arotating cylinder produces a pressure differential. This is thesame effect that makes a baseball curve or a golf ball slice.

Leading EdgeStagnation Point

Trailing EdgeStagnation Point

B

A

Figure 2-3. Air circulation around an airfoil occurs when thefront stagnation point is below the leading edge and the aftstagnation point is beyond the trailing edge.

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he stated that an increase in the speed of movementor flow would cause a decrease in the fluid’spressure. This is exactly what happens to air passingover the curved top of the airplane wing.

An appropriate analogy can be made with waterflowing through a garden hose. Water moving througha hose of constant diameter exerts a uniform pressureon the hose; but if the diameter of a section of the hoseis increased or decreased, it is certain to change thepressure of the water at that point. Suppose the hosewas pinched, thereby constricting the area throughwhich the water flows. Assuming that the same volumeof water flows through the constricted portion of thehose in the same period of time as before the hose waspinched, it follows that the speed of flow must increaseat that point.

Therefore, if a portion of the hose is constricted, it notonly increases the speed of the flow, but also decreasesthe pressure at that point. Like results could beachieved if streamlined solids (airfoils) wereintroduced at the same point in the hose. This sameprinciple is the basis for the measurement of airspeed(fluid flow) and for analyzing the airfoil’s ability toproduce lift.

A practical application of Bernoulli’s theorem is theventuri tube. The venturi tube has an air inlet whichnarrows to a throat (constricted point) and an outletsection which increases in diameter toward the rear.The diameter of the outlet is the same as that of theinlet. At the throat, the airflow speeds up and thepressure decreases; at the outlet, the airflow slowsand the pressure increases. [Figure 2-4]

If air is recognized as a body and it is accepted that itmust follow the above laws, one can begin to seehow and why an airplane wing develops lift as itmoves through the air.

AIRFOIL DESIGNIn the sections devoted to Newton’s and Bernoulli’sdiscoveries, it has already been discussed in general

terms the question of how an airplane wing cansustain flight when the airplane is heavier than air.Perhaps the explanation can best be reduced to itsmost elementary concept by stating that lift (flight)is simply the result of fluid flow (air) about anairfoil—or in everyday language, the result ofmoving an airfoil (wing), by whatever means,through the air.

Since it is the airfoil which harnesses the forcedeveloped by its movement through the air, adiscussion and explanation of this structure, as well assome of the material presented in previous discussionson Newton’s and Bernoulli’s laws, will be presented.

An airfoil is a structure designed to obtain reactionupon its surface from the air through which it moves orthat moves past such a structure. Air acts in variousways when submitted to different pressures andvelocities; but this discussion will be confined to theparts of an airplane that a pilot is most concerned within flight—namely, the airfoils designed to produce lift.By looking at a typical airfoil profile, such as the crosssection of a wing, one can see several obviouscharacteristics of design. [Figure 2-5] Notice that thereis a difference in the curvatures of the upper and lowersurfaces of the airfoil (the curvature is called camber).The camber of the upper surface is more pronouncedthan that of the lower surface, which is somewhat flatin most instances.

In figure 2-5, note that the two extremities of theairfoil profile also differ in appearance. The endwhich faces forward in flight is called the leadingedge, and is rounded; while the other end, thetrailing edge, is quite narrow and tapered.

LeadingEdge

Trailing Edge

Camber of Upper Surface

Camber of Lower Surface

Chord Line

Figure 2-5.Typical airfoil section.

Velocity Pressure

LOW HIGH LOW HIGH

Velocity Pressure

LOW HIGH LOW HIGH

Velocity Pressure

LOW HIGH LOW HIGH

Figure 2-4. Air pressure decreases in a venturi.

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A reference line often used in discussing the airfoil isthe chord line, a straight line drawn through the profileconnecting the extremities of the leading and trailingedges. The distance from this chord line to the upperand lower surfaces of the wing denotes the magnitudeof the upper and lower camber at any point. Anotherreference line, drawn from the leading edge to thetrailing edge, is the “mean camber line.” This mean lineis equidistant at all points from the upper andlower contours.

The construction of the wing, so as to provide actionsgreater than its weight, is done by shaping the wing sothat advantage can be taken of the air’s response tocertain physical laws, and thus develop two actionsfrom the air mass; a positive pressure lifting actionfrom the air mass below the wing, and a negativepressure lifting action from lowered pressure above thewing.

As the airstream strikes the relatively flat lower surfaceof the wing when inclined at a small angle to itsdirection of motion, the air is forced to rebounddownward and therefore causes an upward reactionin positive lift, while at the same time airstreamstriking the upper curved section of the “leadingedge” of the wing is deflected upward. In otherwords, a wing shaped to cause an action on the air,and forcing it downward, will provide an equalreaction from the air, forcing the wing upward. If awing is constructed in such form that it will cause alift force greater than the weight of the airplane, theairplane will fly.

However, if all the lift required were obtained merelyfrom the deflection of air by the lower surface of thewing, an airplane would need only a flat wing like akite. This, of course, is not the case at all; under certainconditions disturbed air currents circulating at thetrailing edge of the wing could be so excessive as tomake the airplane lose speed and lift. The balance ofthe lift needed to support the airplane comes from theflow of air above the wing. Herein lies the key to flight.The fact that most lift is the result of the airflow’sdownwash from above the wing, must be thoroughlyunderstood in order to continue further in the study offlight. It is neither accurate nor does it serve a usefulpurpose, however, to assign specific values to thepercentage of lift generated by the upper surface of anairfoil versus that generated by the lower surface.These are not constant values and will vary, not onlywith flight conditions, but with different wing designs.

It should be understood that different airfoils havedifferent flight characteristics. Many thousands ofairfoils have been tested in wind tunnels and in actualflight, but no one airfoil has been found that satisfiesevery flight requirement. The weight, speed, and

purpose of each airplane dictate the shape of itsairfoil. It was learned many years ago that the mostefficient airfoil for producing the greatest lift wasone that had a concave, or “scooped out” lowersurface. Later it was also learned that as a fixeddesign, this type of airfoil sacrificed too much speedwhile producing lift and, therefore, was not suitablefor high-speed flight. It is interesting to note,however, that through advanced progress inengineering, today’s high-speed jets can again takeadvantage of the concave airfoil’s high liftcharacteristics. Leading edge (Kreuger) flaps andtrailing edge (Fowler) flaps, when extended from thebasic wing structure, literally change theairfoil shape into the classic concave form,thereby generating much greater lift during slowflight conditions.

On the other hand, an airfoil that is perfectlystreamlined and offers little wind resistancesometimes does not have enough lifting power totake the airplane off the ground. Thus, modernairplanes have airfoils which strike a mediumbetween extremes in design, the shape varyingaccording to the needs of the airplane for which it isdesigned. Figure 2-6 shows some of the morecommon airfoil sections.

LOW PRESSURE ABOVEIn a wind tunnel or in flight, an airfoil is simply astreamlined object inserted into a moving stream ofair. If the airfoil profile were in the shape of ateardrop, the speed and the pressure changes of theair passing over the top and bottom would be thesame on both sides. But if the teardrop shaped airfoilwere cut in half lengthwise, a form resembling thebasic airfoil (wing) section would result. If theairfoil were then inclined so the airflow strikes it atan angle (angle of attack), the air molecules movingover the upper surface would be forced to movefaster than would the molecules moving along thebottom of the airfoil, since the upper molecules musttravel a greater distance due to the curvature of theupper surface. This increased velocity reduces thepressure above the airfoil.

Early Airfoil Laminar Flow Airfoil(Subsonic)

Later AirfoilCircular Arc Airfoil

(Supersonic)

Double Wedge Airfoil(Supersonic)

Clark 'Y' Airfoil(Subsonic)

Figure 2-6. Airfoil designs.

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Bernoulli’s principle of pressure by itself does notexplain the distribution of pressure over the uppersurface of the airfoil. A discussion of the influence ofmomentum of the air as it flows in various curvedpaths near the airfoil will be presented. [Figure 2-7]Momentum is the resistance a moving body offers tohaving its direction or amount of motion changed.When a body is forced to move in a circular path, itoffers resistance in the direction away from thecenter of the curved path. This is “centrifugal force.”While the particles of air move in the curved pathAB, centrifugal force tends to throw them in thedirection of the arrows between A and B and hence,causes the air to exert more than normal pressure onthe leading edge of the airfoil. But after the airparticles pass B (the point of reversal of thecurvature of the path) the centrifugal force tends tothrow them in the direction of the arrows between Band C (causing reduced pressure on the airfoil). Thiseffect is held until the particles reach C, the secondpoint of reversal of curvature of the airflow. Againthe centrifugal force is reversed and the particlesmay even tend to give slightly more than normalpressure on the trailing edge of the airfoil, asindicated by the short arrows between C and D.

Therefore, the air pressure on the upper surface ofthe airfoil is distributed so that the pressure is muchgreater on the leading edge than the surroundingatmospheric pressure, causing strong resistance toforward motion; but the air pressure is less thansurrounding atmospheric pressure over a largeportion of the top surface (B to C).

As seen in the application of Bernoulli’s theorem to aventuri, the speedup of air on the top of an airfoilproduces a drop in pressure. This lowered pressure is acomponent of total lift. It is a mistake, however, toassume that the pressure difference between the upperand lower surface of a wing alone accounts for the totallift force produced.

One must also bear in mind that associated with thelowered pressure is downwash; a downward backwardflow from the top surface of the wing. As already seenfrom previous discussions relative to the dynamicaction of the air as it strikes the lower surface of thewing, the reaction of this downward backward flow

results in an upward forward force on the wing. Thissame reaction applies to the flow of air over the topof the airfoil as well as to the bottom, and Newton’sthird law is again in the picture.

HIGH PRESSURE BELOWIn the section dealing with Newton’s laws as theyapply to lift, it has already been discussed how acertain amount of lift is generated by pressureconditions underneath the wing. Because of themanner in which air flows underneath the wing, apositive pressure results, particularly at higherangles of attack. But there is another aspect to thisairflow that must be considered. At a point close tothe leading edge, the airflow is virtually stopped(stagnation point) and then gradually increasesspeed. At some point near the trailing edge, it hasagain reached a velocity equal to that on the uppersurface. In conformance with Bernoulli’s principles,where the airflow was slowed beneath the wing, apositive upward pressure was created against thewing; i.e., as the fluid speed decreases, the pressuremust increase. In essence, this simply “accentuatesthe positive” since it increases the pressuredifferential between the upper and lower surface ofthe airfoil, and therefore increases total lift over thatwhich would have resulted had there been noincrease of pressure at the lower surface. BothBernoulli’s principle and Newton’s laws are inoperation whenever lift is being generated byan airfoil.

Fluid flow or airflow then, is the basis for flight inairplanes, and is a product of the velocity of theairplane. The velocity of the airplane is veryimportant to the pilot since it affects the lift and dragforces of the airplane. The pilot uses the velocity(airspeed) to fly at a minimum glide angle, atmaximum endurance, and for a number of otherflight maneuvers. Airspeed is the velocity of theairplane relative to the air mass through which itis flying.

PRESSURE DISTRIBUTIONFrom experiments conducted on wind tunnel modelsand on full size airplanes, it has been determined thatas air flows along the surface of a wing at differentangles of attack, there are regions along the surfacewhere the pressure is negative, or less thanatmospheric, and regions where the pressure ispositive, or greater than atmospheric. This negativepressure on the upper surface creates a relativelylarger force on the wing than is caused by thepositive pressure resulting from the air striking thelower wing surface. Figure 2-8 shows the pressuredistribution along an airfoil at three different anglesof attack. In general, at high angles of attack the

IncreasedPressure

IncreasedPressure

ReducedPressure

C

DA

B

Figure 2-7. Momentum influences airflow over an airfoil.

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center of pressure moves forward, while at lowangles of attack the center of pressure moves aft. Inthe design of wing structures, this center of pressuretravel is very important, since it affects the positionof the airloads imposed on the wing structure in lowangle-of-attack conditions and high angle-of-attackconditions. The airplane’s aerodynamic balance andcontrollability are governed by changes in the centerof pressure.

The center of pressure is determined throughcalculation and wind tunnel tests by varying theairfoil’s angle of attack through normal operatingextremes. As the angle of attack is changed, so arethe various pressure distribution characteristics.[Figure 2-8] Positive (+) and negative (–) pressureforces are totaled for each angle of attack and theresultant force is obtained. The total resultantpressure is represented by the resultant force vectorshown in figure 2-9.

The point of application of this force vector istermed the “center of pressure” (CP). For any given

angle of attack, the center of pressure is the pointwhere the resultant force crosses the chord line. Thispoint is expressed as a percentage of the chord of theairfoil. A center of pressure at 30 percent of a 60-inch chord would be 18 inches aft of the wing’sleading edge. It would appear then that if thedesigner would place the wing so that its center ofpressure was at the airplane’s center of gravity, theairplane would always balance. The difficulty arises,however, that the location of the center of pressurechanges with change in the airfoil’s angle of attack.[Figure 2-10]

In the airplane’s normal range of flight attitudes, ifthe angle of attack is increased, the center ofpressure moves forward; and if decreased, it movesrearward. Since the center of gravity is fixed at onepoint, it is evident that as the angle of attackincreases, the center of lift (CL) moves ahead of thecenter of gravity, creating a force which tends toraise the nose of the airplane or tends to increase theangle of attack still more. On the other hand, if theangle of attack is decreased, the center of lift (CL)moves aft and tends to decrease the angle a greateramount. It is seen then, that the ordinary airfoil isinherently unstable, and that an auxiliary device,such as the horizontal tail surface, must be added tomake the airplane balance longitudinally.

The balance of an airplane in flight depends, therefore,on the relative position of the center of gravity (CG)and the center of pressure (CP) of the airfoil.Experience has shown that an airplane with the center

+4°

+10°Angle ofAttack

Angle ofAttack

-8°Angle ofAttack

Figure 2-8. Pressure distribution on an airfoil.

Chord LineAngle ofAttack

Relative Wind

Lift

Drag

Res

ulta

ntFo

rce

Center ofPressure

Figure 2-9. Force vectors on an airfoil.

Angle of Attack

Angle of Attack

Angle of Attack

CP

CP

CP

CG

CG

CG

Figure 2-10. CP changes with an angle of attack.

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of gravity in the vicinity of 20 percent of the wingchord can be made to balance and fly satisfactorily.

The tapered wing presents a variety of wing chordsthroughout the span of the wing. It becomesnecessary then, to specify some chord about whichthe point of balance can be expressed. This chord,known as the mean aerodynamic chord (MAC),

usually is defined as the chord of an imaginaryuntapered wing, which would have the same centerof pressure characteristics as the wing in question.

Airplane loading and weight distribution also affectcenter of gravity and cause additional forces, whichin turn affect airplane balance.

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FORCES ACTING ON THE AIRPLANEIn some respects at least, how well a pilot performs inflight depends upon the ability to plan and coordinatethe use of the power and flight controls for changingthe forces of thrust, drag, lift, and weight. It is the bal-ance between these forces that the pilot must alwayscontrol. The better the understanding of the forces andmeans of controlling them, the greater will be thepilot’s skill at doing so.

The following defines these forces in relation tostraight-and-level, unaccelerated flight.

Thrust is the forward force produced by the power-plant/propeller. It opposes or overcomes the force ofdrag. As a general rule, it is said to act parallel to thelongitudinal axis. However, this is not always the caseas will be explained later.

Drag is a rearward, retarding force, and is caused bydisruption of airflow by the wing, fuselage, and otherprotruding objects. Drag opposes thrust, and acts rear-ward parallel to the relative wind.

Weight is the combined load of the airplane itself, thecrew, the fuel, and the cargo or baggage. Weight pullsthe airplane downward because of the force of gravity.It opposes lift, and acts vertically downward throughthe airplane’s center of gravity.

Lift opposes the downward force of weight, is pro-duced by the dynamic effect of the air acting on thewing, and acts perpendicular to the flightpath throughthe wing’s center of lift.

In steady flight, the sum of these opposing forces isequal to zero. There can be no unbalanced forces insteady, straight flight (Newton’s Third Law). This istrue whether flying level or when climbing ordescending. This is not the same thing as saying thatthe four forces are all equal. It simply means thatthe opposing forces are equal to, and thereby cancelthe effects of, each other. Often the relationshipbetween the four forces has been erroneouslyexplained or illustrated in such a way that this pointis obscured. Consider figure 3-1 on the next page,for example. In the upper illustration the force vectorsof thrust, drag, lift, and weight appear to be equal invalue. The usual explanation states (without stipulat-ing that thrust and drag do not equal weight and lift)that thrust equals drag and lift equals weight as shownin the lower illustration. This basically true statementmust be understood or it can be misleading. It shouldbe understood that in straight, level, unacceleratedflight, it is true that the opposing lift/weight forcesare equal, but they are also greater than the oppos-ing forces of thrust/drag that are equal only to eachother; not to lift/weight. To be correct about it, itmust be said that in steady flight:

• The sum of all upward forces (not just lift) equalsthe sum of all downward forces (not just weight).

• The sum of all forward forces (not just thrust)equals the sum of all backward forces (not justdrag).

This refinement of the old “thrust equals drag; liftequals weight” formula takes into account the fact that

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in climbs a portion of thrust, since it is directed upward,acts as if it were lift; and a portion of weight, since it isdirected backward, acts as if it were drag. In glides, aportion of the weight vector is directed forward, andtherefore acts as thrust. In other words, any time theflightpath of the airplane is not horizontal, lift, weight,thrust, and drag vectors must each be broken down intotwo components. [Figure 3-2]

Figure 3-2. Force vectors during a stabilized climb.

Discussions of the preceding concepts are frequentlyomitted in aeronautical texts/handbooks/manuals. Thereason is not that they are of no consequence, butbecause by omitting such discussions, the main ideaswith respect to the aerodynamic forces acting upon

an airplane in flight can be presented in their mostessential elements without being involved in thetechnicalities of the aerodynamicist. In point of fact,considering only level flight, and normal climbs andglides in a steady state, it is still true that wing lift isthe really important upward force, and weight is thereally important downward force.

Frequently, much of the difficulty encountered inexplaining the forces that act upon an airplane is largelya matter of language and its meaning. For example,pilots have long believed that an airplane climbsbecause of excess lift. This is not true if one is thinkingin terms of wing lift alone. It is true, however, if by liftit is meant the sum total of all “upward forces.” Butwhen referring to the “lift of thrust” or the “thrust ofweight,” the definitions previously established forthese forces are no longer valid and complicate mat-ters. It is this impreciseness in language that affords theexcuse to engage in arguments, largely academic, overrefinements to basic principles.

Though the forces acting on an airplane have alreadybeen defined, a discussion in more detail to establishhow the pilot uses them to produce controlled flightis appropriate.

THRUSTBefore the airplane begins to move, thrust must beexerted. It continues to move and gain speed untilthrust and drag are equal. In order to maintain a con-stant airspeed, thrust and drag must remain equal,just as lift and weight must be equal to maintain aconstant altitude. If in level flight, the engine poweris reduced, the thrust is lessened, and the airplaneslows down. As long as the thrust is less than thedrag, the airplane continues to decelerate until itsairspeed is insufficient to support it in the air.

Likewise, if the engine power is increased, thrustbecomes greater than drag and the airspeedincreases. As long as the thrust continues to begreater than the drag, the airplane continues to accel-erate. When drag equals thrust, the airplane flies at aconstant airspeed.

Straight-and-level flight may be sustained at speedsfrom very slow to very fast. The pilot must coordi-nate angle of attack and thrust in all speed regimes ifthe airplane is to be held in level flight. Roughly,these regimes can be grouped in three categories:low-speed flight, cruising flight, and high-speedflight.

When the airspeed is low, the angle of attack must berelatively high to increase lift if the balance betweenlift and weight is to be maintained. [Figure 3-3] Ifthrust decreases and airspeed decreases, lift becomes

Figure 3-1. Relationship of forces acting on an airplane.

Incorrect Relationship

Correct Relationship

Weight

Weight

Lift

Lift

Thrust

Thrust

Drag

Drag

Drag

Thrust

Flight Path

Relative Wind

Component of Weight Opposed

to Lift

Rearward Componentof Weight

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less than weight and the airplane will start todescend. To maintain level flight, the pilot canincrease the angle of attack an amount which willgenerate a lift force again equal to the weight of theairplane and while the airplane will be flying moreslowly, it will still maintain level flight if the pilothas properly coordinated thrust and angle of attack.

Straight-and-level flight in the slow speed regimeprovides some interesting conditions relative to theequilibrium of forces, because with the airplane in anose-high attitude, there is a vertical component ofthrust that helps support the airplane. For one thing,wing loading tends to be less than would beexpected. Most pilots are aware that an airplane willstall, other conditions being equal, at a slower speedwith the power on than with the power off. (Inducedairflow over the wings from the propeller also con-tributes to this.) However, if analysis is restricted tothe four forces as they are usually defined, one cansay that in straight-and-level slow speed flight thethrust is equal to drag, and lift is equal to weight.

During straight-and level-flight when thrust isincreased and the airspeed increases, the angle ofattack must be decreased. That is, if changes havebeen coordinated, the airplane will still remain inlevel flight but at a higher speed when the properrelationship between thrust and angle of attack isestablished.

If the angle of attack were not coordinated(decreased) with this increase of thrust, the airplanewould climb. But decreasing the angle of attackmodifies the lift, keeping it equal to the weight, andif properly done, the airplane still remains in levelflight. Level flight at even slightly negative angles ofattack is possible at very high speed. It is evidentthen, that level flight can be performed with anyangle of attack between stalling angle and the rela-tively small negative angles found at high speed.

DRAGDrag in flight is of two basic types: parasite dragand induced drag. The first is called parasitebecause it in no way functions to aid flight, whilethe second is induced or created as a result of thewing developing lift.

Parasite drag is composed of two basic elements:form drag, resulting from the disruption of thestreamline flow; and the resistance of skin friction.

Of the two components of parasite drag, form drag isthe easier to reduce when designing an airplane. Ingeneral, a more streamlined object produces the bestform to reduce parasite drag.

Skin friction is the type of parasite drag that is mostdifficult to reduce. No surface is perfectly smooth.Even machined surfaces, when inspected throughmagnification, have a ragged, uneven appearance.This rough surface will deflect the streamlines of airon the surface, causing resistance to smooth airflow.Skin friction can be minimized by employing a glossy,flat finish to surfaces, and by eliminating protrudingrivet heads, roughness, and other irregularities.

Another element must be added to the considera-tion of parasite drag when designing an airplane.This drag combines the effects of form drag andskin friction and is called interference drag. If twoobjects are placed adjacent to one another, theresulting turbulence produced may be 50 to 200percent greater than the parts tested separately.

The three elements, form drag, skin friction, andinterference drag, are all computed to determineparasite drag on an airplane.

Shape of an object is a big factor in parasite drag.However, indicated airspeed is an equally importantfactor when speaking of parasite drag. The profiledrag of a streamlined object held in a fixed positionrelative to the airflow increases approximately as thesquare of the velocity; thus, doubling the airspeedincreases the drag four times, and tripling the airspeedincreases the drag nine times. This relationship, how-ever, holds good only at comparatively low subsonicspeeds. At some higher airspeeds, the rate at whichprofile drag has been increased with speed suddenlybegins to increase more rapidly.

The second basic type of drag is induced drag. It isan established physical fact that no system, whichdoes work in the mechanical sense, can be 100 per-cent efficient. This means that whatever the nature

Flight Path

Relative Wind

12°

Level (Low Speed)

Flight Path

Relative Wind

6°

Level (Cruise Speed)

Flight Path

Relative Wind

3°

Level (High Speed)

Figure 3-3. Angle of attack at various speeds.

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of the system, the required work is obtained at theexpense of certain additional work that is dissipatedor lost in the system. The more efficient the system,the smaller this loss.

In level flight the aerodynamic properties of the wingproduce a required lift, but this can be obtained onlyat the expense of a certain penalty. The name given tothis penalty is induced drag. Induced drag is inherentwhenever a wing is producing lift and, in fact, thistype of drag is inseparable from the production of lift.Consequently, it is always present if lift is produced.

The wing produces the lift force by making use ofthe energy of the free airstream. Whenever the wingis producing lift, the pressure on the lower surface ofthe wing is greater than that on the upper surface. Asa result, the air tends to flow from the high pressurearea below the wingtip upward to the low pressurearea above the wing. In the vicinity of the wingtips,there is a tendency for these pressures to equalize,resulting in a lateral flow outward from the under-side to the upper surface of the wing. This lateralflow imparts a rotational velocity to the air at thewingtips and trails behind the wing. Therefore, flowabout the wingtips will be in the form of two vorticestrailing behind as the wings move on.

When the airplane is viewed from the tail, thesevortices will circulate counterclockwise about theright wingtip and clockwise about the left wingtip.[Figure 3-4] Bearing in mind the direction of rota-tion of these vortices, it can be seen that they inducean upward flow of air beyond the wingtip, and adownwash flow behind the wing’s trailing edge. Thisinduced downwash has nothing in common with thedownwash that is necessary to produce lift. It is, infact, the source of induced drag. The greater the sizeand strength of the vortices and consequent down-wash component on the net airflow over the wing,the greater the induced drag effect becomes. Thisdownwash over the top of the wing at the tip has thesame effect as bending the lift vector rearward;therefore, the lift is slightly aft of perpendicular tothe relative wind, creating a rearward lift component.This is induced drag.

It should be remembered that in order to create agreater negative pressure on the top of the wing, thewing can be inclined to a higher angle of attack; also,that if the angle of attack of an asymmetrical wingwere zero, there would be no pressure differentialand consequently no downwash component; there-fore, no induced drag. In any case, as angle of attackincreases, induced drag increases proportionally.

To state this another way—the lower the airspeed thegreater the angle of attack required to produce lift

equal to the airplane’s weight and consequently, thegreater will be the induced drag. The amount ofinduced drag varies inversely as the square of theairspeed.

From the foregoing discussion, it can be noted thatparasite drag increases as the square of the airspeed,and induced drag varies inversely as the square ofthe airspeed. It can be seen that as airspeeddecreases to near the stalling speed, the total dragbecomes greater, due mainly to the sharp rise ininduced drag. Similarly, as the airspeed reaches theterminal velocity of the airplane, the total dragagain increases rapidly, due to the sharp increaseof parasite drag. As seen in figure 3-5, at somegiven airspeed, total drag is at its maximumamount. This is very important in figuring themaximum endurance and range of airplanes; forwhen drag is at a minimum, power required toovercome drag is also at a minimum.

To understand the effect of lift and drag on an air-plane in flight, both must be combined and thelift/drag ratio considered. With the lift and drag data

AirflowAbove Wing

AirflowBelow Wing

Air Spillage

Vorte

x

Figure 3-4. Wingtip vortices.

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available for various airspeeds of the airplane insteady, unaccelerated flight, the proportions of CL(Coefficient of Lift) and CD (Coefficient of Drag)can be calculated for each specific angle of attack.The resulting plot for lift/drag ratio with angle ofattack shows that L/D increases to some maximum,then decreases at the higher lift coefficients andangles of attack, as shown in figure 3-6. Note thatthe maximum lift/drag ratio, (L/D max) occurs at onespecific angle of attack and lift coefficient. If the air-plane is operated in steady flight at L/D max, thetotal drag is at a minimum. Any angle of attack loweror higher than that for L/D max reduces the lift/dragratio and consequently increases the total drag for agiven airplane’s lift.

The location of the center of gravity (CG) is determinedby the general design of each particular airplane. The

designers determine how far the center of pressure (CP)will travel. They then fix the center of gravity forwardof the center of pressure for the corresponding flightspeed in order to provide an adequate restoring momentto retain flight equilibrium.

The configuration of an airplane has a great effect onthe lift/drag ratio. The high performance sailplanemay have extremely high lift/drag ratios. The super-sonic fighter may have seemingly low lift/drag ratiosin subsonic flight, but the airplane configurationsrequired for supersonic flight (and high L/Ds at highMach numbers) cause this situation.

WEIGHTGravity is the pulling force that tends to draw allbodies to the center of the earth. The center of gravity(CG) may be considered as a point at which all theweight of the airplane is concentrated. If the airplanewere supported at its exact center of gravity, it wouldbalance in any attitude. It will be noted that center ofgravity is of major importance in an airplane, for itsposition has a great bearing upon stability.

The location of the center of gravity is determinedby the general design of each particular airplane. Thedesigners determine how far the center of pressure(CP) will travel. They then fix the center of gravityforward of the center of pressure for the correspon-ding flight speed in order to provide an adequaterestoring moment to retain flight equilibrium.

Weight has a definite relationship with lift, and thrustwith drag. This relationship is simple, but importantin understanding the aerodynamics of flying. Lift

is the upward force onthe wing acting perpen-dicular to the relativewind. Lift is required tocounteract the airplane’sweight (which is causedby the force of gravityacting on the mass of theairplane). This weight(gravity) force actsdownward through theairplane’s center ofgravity. In stabilizedlevel flight, when the liftforce is equal to theweight force, the air-plane is in a state ofequilibrium and neithergains nor loses altitude.If lift becomes less thanweight, the airplane loses

Figure 3-5. Drag versus speed.

Dra

g -

Pou

nds Parasite Drag

Induced Drag

Total Drag

Speed

Sta

ll

(L/D)MAX

L/D

CLMAX

CD

CD

CLCL

STALL

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

18

16

14

12

10

8

6

4

2

0

LD

00

2 4 6 8 10 12 14 16 18 20 22

.2000

.1800

.1600

.1400

.1200

.1000

.0800

.0600

.0400

.0200

Angle of Attack, Degrees

Figure 3-6. Lift coefficients at various angles of attack.

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altitude. When the lift is greater than weight, the air-plane gains altitude.

LIFTThe pilot can control the lift. Any time the controlwheel is more fore or aft, the angle of attack ischanged. As angle of attack increases, lift increases(all other factors being equal). When the airplanereaches the maximum angle of attack, lift begins todiminish rapidly. This is the stalling angle of attack,or burble point.

Before proceeding further with lift and how it can becontrolled, velocity must be interjected. The shapeof the wing cannot be effective unless it continuallykeeps “attacking” new air. If an airplane is to keepflying, it must keep moving. Lift is proportional tothe square of the airplane’s velocity. For example, anairplane traveling at 200 knots has four times the liftas the same airplane traveling at 100 knots, if theangle of attack and other factors remain constant.

Actually, the airplane could not continue to travel inlevel flight at a constant altitude and maintain thesame angle of attack if the velocity is increased. Thelift would increase and the airplane would climb asa result of the increased lift force. Therefore, tomaintain the lift and weight forces in balance, andto keep the airplane “straight and level” (not accel-erating upward) in a state of equilibrium, as velocityis increased, lift must be decreased. This is normallyaccomplished by reducing the angle of attack; i.e.,lowering the nose. Conversely, as the airplane isslowed, the decreasing velocity requires increasingthe angle of attack to maintain lift sufficient tomaintain flight. There is, of course, a limit to howfar the angle of attack can be increased, if a stall isto be avoided.

Therefore, it may be concluded that for every angleof attack there is a corresponding indicated airspeedrequired to maintain altitude in steady, unacceleratedflight—all other factors being constant. (Bear inmind this is only true if maintaining “level flight.”)Since an airfoil will always stall at the same angleof attack, if increasing weight, lift must also beincreased, and the only method for doing so is byincreased velocity if the angle of attack is heldconstant just short of the “critical” or stalling angleof attack.

Lift and drag also vary directly with the density ofthe air. Density is affected by several factors: pres-sure, temperature, and humidity. Remember, at analtitude of 18,000 feet, the density of the air hasone-half the density of air at sea level. Therefore,in order to maintain its lift at a higher altitude, an

airplane must fly at a greater true airspeed for anygiven angle of attack.

Furthermore, warm air is less dense than cool air,and moist air is less dense than dry air. Thus, on ahot humid day, an airplane must be flown at a greatertrue airspeed for any given angle of attack than on acool, dry day.

If the density factor is decreased and the total liftmust equal the total weight to remain in flight, itfollows that one of the other factors must beincreased. The factors usually increased are the air-speed or the angle of attack, because these factorscan be controlled directly by the pilot.

It should also be pointed out that lift varies directlywith the wing area, provided there is no change inthe wing’s planform. If the wings have the same pro-portion and airfoil sections, a wing with a planformarea of 200 square feet lifts twice as much at thesame angle of attack as a wing with an area of 100square feet.

As can be seen, two major factors from the pilot’sviewpoint are lift and velocity because these are thetwo that can be controlled most readily and accu-rately. Of course, the pilot can also control densityby adjusting the altitude and can control wing areaif the airplane happens to have flaps of the type thatenlarge wing area. However, for most situations, thepilot is controlling lift and velocity to maneuver theairplane. For instance, in straight-and-level flight,cruising along at a constant altitude, altitude ismaintained by adjusting lift to match the airplane’svelocity or cruise airspeed, while maintaining astate of equilibrium where lift equals weight. In anapproach to landing, when the pilot wishes to landas slowly as practical, it is necessary to increase liftto near maximum to maintain lift equal to the weightof the airplane.

WINGTIP VORTICESThe action of the airfoil that gives an airplane liftalso causes induced drag. It was determined thatwhen a wing is flown at a positive angle of attack, apressure differential exists between the upper andlower surfaces of the wing—that is, the pressureabove the wing is less than atmospheric pressure andthe pressure below the wing is equal to or greaterthan atmospheric pressure. Since air always movesfrom high pressure toward low pressure, and the pathof least resistance is toward the airplane’s wingtips,there is a spanwise movement of air from the bottomof the wing outward from the fuselage around thewingtips. This flow of air results in “spillage” overthe wingtips, thereby setting up a whirlpool of air

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called a “vortex.” [Figure 3-4] At the same time, theair on the upper surface of the wing has a tendencyto flow in toward the fuselage and off the trailingedge. This air current forms a similar vortex at theinboard portion of the trailing edge of the wing,but because the fuselage limits the inward flow, thevortex is insignificant. Consequently, the deviationin flow direction is greatest at the wingtips wherethe unrestricted lateral flow is the strongest. As theair curls upward around the wingtip, it combineswith the wing’s downwash to form a fast spinningtrailing vortex. These vortices increase dragbecause of energy spent in producing the turbu-lence. It can be seen, then, that whenever the wingis producing lift, induced drag occurs, and wingtipvortices are created.

Just as lift increases with an increase in angle ofattack, induced drag also increases. This occursbecause as the angle of attack is increased, there is agreater pressure difference between the top and bot-tom of the wing, and a greater lateral flow of air;consequently, this causes more violent vortices to beset up, resulting in more turbulence and moreinduced drag.

The intensity or strength of the wingtip vortices isdirectly proportional to the weight of the airplane andinversely proportional to the wingspan and speed ofthe airplane. The heavier and slower the airplane, thegreater the angle of attack and the stronger the wingtipvortices. Thus, an airplane will create wingtip vorticeswith maximum strength occurring during the takeoff,climb, and landing phases of flight.

GROUND EFFECTIt is possible to fly an airplane just clear of theground (or water) at a slightly slower airspeedthan that required to sustain level flight at higheraltitudes. This is the result of a phenomenon,which is better known than understood even bysome experienced pilots.

When an airplane in flightgets within several feetfrom the ground surface, achange occurs in the three-dimensional flow patternaround the airplane becausethe vertical component ofthe airflow around the wingis restricted by the groundsurface. This alters thewing’s upwash, downwash,and wingtip vortices.[Figure 3-7] These generaleffects due to the presence

of the ground are referred to as “ground effect.”Ground effect, then, is due to the interference of theground (or water) surface with the airflow patternsabout the airplane in flight.

While the aerodynamic characteristics of the tail sur-faces and the fuselage are altered by ground effects,the principal effects due to proximity of the groundare the changes in the aerodynamic characteristics ofthe wing. As the wing encounters ground effect andis maintained at a constant lift coefficient, there isconsequent reduction in the upwash, downwash, andthe wingtip vortices.

Induced drag is a result of the wing’s work of sus-taining the airplane and the wing lifts the airplanesimply by accelerating a mass of air downward. Itis true that reduced pressure on top of an airfoil isessential to lift, but that is but one of the thingsthat contributes to the overall effect of pushing anair mass downward. The more downwash there is,the harder the wing is pushing the mass of airdown. At high angles of attack, the amount ofinduced drag is high and since this corresponds tolower airspeeds in actual flight, it can be said thatinduced drag predominates at low speed.

However, the reduction of the wingtip vortices dueto ground effect alters the spanwise lift distributionand reduces the induced angle of attack and induceddrag. Therefore, the wing will require a lower angleof attack in ground effect to produce the same liftcoefficient or, if a constant angle of attack is main-tained, an increase in lift coefficient will result.[Figure 3-8]

Figure 3-7. Ground effect changes airflow.

InGround Effect

InGround Effect

Out ofGround Effect

Out ofGround Effect

Angle of Attack

Lift

Coe

ffici

ent C

L

Velocity

Thr

ust R

equi

red

Figure 3-8. Ground effect changes drag and lift.

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Ground effect also will alter the thrust required ver-sus velocity. Since induced drag predominates at lowspeeds, the reduction of induced drag due to groundeffect will cause the most significant reduction ofthrust required (parasite plus induced drag) at lowspeeds.

The reduction in induced flow due to ground effectcauses a significant reduction in induced drag butcauses no direct effect on parasite drag. As a resultof the reduction in induced drag, the thrust requiredat low speeds will be reduced.

Due to the change in upwash, downwash, andwingtip vortices, there may be a change in position(installation) error of the airspeed system, associatedwith ground effect. In the majority of cases, groundeffect will cause an increase in the local pressure atthe static source and produce a lower indication ofairspeed and altitude. Thus, the airplane may be air-borne at an indicated airspeed less than that normallyrequired.

In order for ground effect to be of significant magni-tude, the wing must be quite close to the ground. Oneof the direct results of ground effect is the variationof induced drag with wing height above the ground ata constant lift coefficient. When the wing is at aheight equal to its span, the reduction in induced dragis only 1.4 percent. However, when the wing is at aheight equal to one-fourth its span, the reduction ininduced drag is 23.5 percent and, when the wing is ata height equal to one-tenth its span, the reduction ininduced drag is 47.6 percent. Thus, a large reductionin induced drag will take place only when the wing isvery close to the ground. Because of this variation,ground effect is most usually recognized during theliftoff for takeoff or just prior to touchdown whenlanding.

During the takeoff phase of flight, ground effect pro-duces some important relationships. The airplaneleaving ground effect after takeoff encounters justthe reverse of the airplane entering ground effectduring landing; i.e., the airplane leaving groundeffect will:

• Require an increase in angle of attack to maintainthe same lift coefficient.

• Experience an increase in induced drag and thrustrequired.

• Experience a decrease in stability and a nose-upchange in moment.

• Produce a reduction in static source pressure andincrease in indicated airspeed.

These general effects should point out the possibledanger in attempting takeoff prior to achieving therecommended takeoff speed. Due to the reduced dragin ground effect, the airplane may seem capable oftakeoff well below the recommended speed.However, as the airplane rises out of ground effectwith a deficiency of speed, the greater induced dragmay result in very marginal initial climb perform-ance. In the extreme conditions such as high grossweight, high density altitude, and high temperature, adeficiency of airspeed during takeoff may permit theairplane to become airborne but be incapable of flyingout of ground effect. In this case, the airplane maybecome airborne initially with a deficiency of speed,and then settle back to the runway. It is important thatno attempt be made to force the airplane to becomeairborne with a deficiency of speed; the recommendedtakeoff speed is necessary to provide adequate initialclimb performance. For this reason, it is imperativethat a definite climb be established before retractingthe landing gear or flaps.

During the landing phase of flight, the effect of prox-imity to the ground also must be understood andappreciated. If the airplane is brought into groundeffect with a constant angle of attack, the airplanewill experience an increase in lift coefficient and areduction in the thrust required. Hence, a “floating”effect may occur. Because of the reduced drag andpower off deceleration in ground effect, any excessspeed at the point of flare may incur a considerable“float” distance. As the airplane nears the point oftouchdown, ground effect will be most realized ataltitudes less than the wingspan. During the finalphases of the approach as the airplane nears theground, a reduced power setting is necessary or thereduced thrust required would allow the airplane toclimb above the desired glidepath.

AXES OF AN AIRPLANEWhenever an airplane changes its flight attitude orposition in flight, it rotates about one or more ofthree axes, which are imaginary lines that passthrough the airplane’s center of gravity. The axes ofan airplane can be considered as imaginary axlesaround which the airplane turns, much like the axlearound which a wheel rotates. At the point where allthree axes intersect, each is at a 90° angle to the othertwo. The axis, which extends lengthwise through thefuselage from the nose to the tail, is the longitudinalaxis. The axis, which extends crosswise fromwingtip to wingtip, is the lateral axis. The axis,which passes vertically through the center of gravity,is the vertical axis. [Figure 3-9]

The airplane’s motion about its longitudinal axisresembles the roll of a ship from side to side. In fact,

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the names used in describing the motion about anairplane’s three axes were originally nautical terms.They have been adapted to aeronautical terminologybecause of the similarity of motion between an air-plane and the seagoing ship.

In light of the adoption of nautical terms, the motionabout the airplane’s longitudinal axis is called “roll”;motion about its lateral axis is referred to as “pitch.”Finally, an airplane moves about its vertical axis in amotion, which is termed “yaw”—that is, a horizontal(left and right) movement of the airplane’s nose.

The three motions of the airplane (roll, pitch, andyaw) are controlled by three control surfaces. Roll iscontrolled by the ailerons; pitch is controlled by theelevators; yaw is controlled by the rudder. The use ofthese controls is explained in Chapter 4—FlightControls.

MOMENTS AND MOMENT ARMA study of physics shows that a body that is free torotate will always turn about its center of gravity. Inaerodynamic terms, the mathematical measure of anairplane’s tendency to rotate about its center ofgravity is called a “moment.” A moment is said to beequal to the product of the force applied and the dis-tance at which the force is applied. (A moment arm isthe distance from a datum [reference point or line] tothe applied force.) For airplane weight and balancecomputations, “moments” are expressed in terms ofthe distance of the arm times the airplane’s weight, orsimply, inch pounds.

Airplane designers locate the fore and aft position ofthe airplane’s center of gravity as nearly as possibleto the 20 percent point of the mean aerodynamicchord (MAC). If the thrust line is designed to passhorizontally through the center of gravity, it will notcause the airplane to pitch when power is changed,and there will be no difference in moment due tothrust for a power-on or power-off condition offlight. Although designers have some control over

the location of the drag forces, they are not alwaysable to make the resultant drag forces pass throughthe center of gravity of the airplane. However, theone item over which they have the greatest controlis the size and location of the tail. The objective isto make the moments (due to thrust, drag, and lift)as small as possible; and, by proper location of thetail, to provide the means of balancing the airplanelongitudinally for any condition of flight.

The pilot has no direct control over the location offorces acting on the airplane in flight, except forcontrolling the center of lift by changing the angleof attack. Such a change, however, immediatelyinvolves changes in other forces. Therefore, thepilot cannot independently change the location ofone force without changing the effect of others. Forexample, a change in airspeed involves a change inlift, as well as a change in drag and a change in theup or down force on the tail. As forces such as tur-bulence and gusts act to displace the airplane, thepilot reacts by providing opposing control forces tocounteract this displacement.

Some airplanes are subject to changes in the locationof the center of gravity with variations of load.Trimming devices are used to counteract the forcesset up by fuel burnoff, and loading or off-loading ofpassengers or cargo. Elevator trim tabs andadjustable horizontal stabilizers comprise the mostcommon devices provided to the pilot for trimmingfor load variations. Over the wide ranges of balanceduring flight in large airplanes, the force which thepilot has to exert on the controls would becomeexcessive and fatiguing if means of trimming werenot provided.

DESIGN CHARACTERISTICSEvery pilot who has flown numerous types of air-planes has noted that each airplane handles somewhatdifferently—that is, each resists or responds tocontrol pressures in its own way. A training typeairplane is quick to respond to control applications,

Lateral Axis

PITCHING

Longitudinal Axis

ROLLING

Vertical Axis

YAWING

Figure 3-9. Axes of an airplane.

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while a transport airplane usually feels heavy on thecontrols and responds to control pressures moreslowly. These features can be designed into an air-plane to facilitate the particular purpose the airplaneis to fulfill by considering certain stability andmaneuvering requirements. In the following discus-sion, it is intended to summarize the more importantaspects of an airplane’s stability; its maneuveringand controllability qualities; how they are analyzed;and their relationship to various flight conditions. Inbrief, the basic differences between stability, maneu-verability, and controllability are as follows:

• Stability—The inherent quality of an airplaneto correct for conditions that may disturb itsequilibrium, and to return or to continue on theoriginal flightpath. It is primarily an airplanedesign characteristic.

• Maneuverability—The quality of an airplanethat permits it to be maneuvered easily and towithstand the stresses imposed by maneuvers. Itis governed by the airplane’s weight, inertia, sizeand location of flight controls, structuralstrength, and powerplant. It too is an airplanedesign characteristic.

• Controllability—The capability of an airplane torespond to the pilot’s control, especially withregard to flightpath and attitude. It is the qualityof the airplane’s response to the pilot’s controlapplication when maneuvering the airplane,regardless of its stability characteristics.

BASIC CONCEPTS OF STABILITYThe flightpaths and attitudes in which an airplanecan fly are limited only by the aerodynamic charac-teristics of the airplane, its propulsive system, and its

structural strength. These limitations indicate themaximum performance and maneuverability of theairplane. If the airplane is to provide maximum util-ity, it must be safely controllable to the full extent ofthese limits without exceeding the pilot’s strengthor requiring exceptional flying ability. If an airplaneis to fly straight and steady along any arbitraryflightpath, the forces acting on it must be in staticequilibrium. The reaction of any body when itsequilibrium is disturbed is referred to as stability.There are two types of stability; static and dynamic.Static will be discussed first, and in this discussionthe following definitions will apply:

• Equilibrium—All opposing forces acting on theairplane are balanced; (i.e., steady, unacceleratedflight conditions).

• Static Stability—The initial tendency that the air-plane displays after its equilibrium is disturbed.

• Positive Static Stability—The initial tendencyof the airplane to return to the original state ofequilibrium after being disturbed. [Figure 3-10]

• Negative Static Stability—The initial tendencyof the airplane to continue away from the originalstate of equilibrium after being disturbed. [Figure3-10]

• Neutral Static Stability—The initial tendencyof the airplane to remain in a new condition afterits equilibrium has been disturbed. [Figure 3-10]

STATIC STABILITYStability of an airplane in flight is slightly more com-plex than just explained, because the airplane is freeto move in any direction and must be controllable in

Figure 3-10.Types of stability.

CG

AppliedForce

POSITIVESTATIC STABILITY

CG

CG

AppliedForce

NEUTRALSTATIC STABILITY

CG

AppliedForce

NEGATIVESTATIC STABILITY

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pitch, roll, and direction. When designing the airplane,engineers must compromise between stability,maneuverability, and controllability; and the problemis compounded because of the airplane’s three-axisfreedom. Too much stability is detrimental tomaneuverability, and similarly, not enough stabil-ity is detrimental to controllability. In the designof airplanes, compromise between the two is thekeyword.

DYNAMIC STABILITYStatic stability has been defined as the initial tendencythat the airplane displays after being disturbed from itstrimmed condition. Occasionally, the initial tendencyis different or opposite from the overall tendency, sodistinction must be made between the two. Dynamicstability is the overall tendency that the airplane dis-plays after its equilibrium is disturbed. The curves offigure 3-11 represent the variation of controlledfunctions versus time. It is seen that the unit of timeis very significant. If the time unit for one cycle oroscillation is above 10 seconds’ duration, it is calleda “long-period” oscillation (phugoid) and is easilycontrolled. In a longitudinal phugoid oscillation,the angle of attack remains constant when the air-speed increases and decreases. To a certain degree,a convergent phugoid is desirable but is notrequired. The phugoid can be determined only on astatically stable airplane, and this has a great effecton the trimming qualities of the airplane. If thetime unit for one cycle or oscillation is less thanone or two seconds, it is called a “short-period”oscillation and is normally very difficult, if notimpossible, for the pilot to control. This is the typeof oscillation that the pilot can easily “get in phasewith” and reinforce.

A neutral or divergent, short-period oscillation isdangerous because structural failure usuallyresults if the oscillation is not damped immedi-ately. Short-period oscillations affect airplane andcontrol surfaces alike and reveal themselves as“porpoising” in the airplane, or as in “buzz” or“flutter” in the control surfaces. Basically, theshort-period oscillation is a change in angle ofattack with no change in airspeed. A short-periodoscillation of a control surface is usually of suchhigh frequency that the airplane does not havetime to react. Logically, the Code of FederalRegulations require that short-period oscillationsbe heavily damped (i.e., die out immediately).Flight tests during the airworthiness certificationof airplanes are conducted for this condition byinducing the oscillation in the controls for pitch,roll, or yaw at the most critical speed (i.e., at VNE,the never-exceed speed). The test pilot strikes thecontrol wheel or rudder pedal a sharp blow andobserves the results.

LONGITUDINAL STABILITY (PITCHING)In designing an airplane, a great deal of effort isspent in developing the desired degree of stabilityaround all three axes. But longitudinal stability aboutthe lateral axis is considered to be the most affectedby certain variables in various flight conditions.

A

Time

Damped Oscillation

(Positive Static)(Positive Dynamic)

Time

Undamped Oscillation

(Positive Static)(Neutral Dynamic)

Time

Divergent Oscillation

(Positive Static)(Negative Dynamic)

Dis

plac

emen

tD

ispl

acem

ent

Dis

plac

emen

t

B

C

Figure 3-11. Damped versus undamped stability.

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Longitudinal stability is the quality that makes anairplane stable about its lateral axis. It involves thepitching motion as the airplane’s nose moves up anddown in flight. A longitudinally unstable airplane hasa tendency to dive or climb progressively into a verysteep dive or climb, or even a stall. Thus, an airplanewith longitudinal instability becomes difficult andsometimes dangerous to fly.

Static longitudinal stability or instability in an air-plane, is dependent upon three factors:

1. Location of the wing with respect to the center ofgravity;

2. Location of the horizontal tail surfaces withrespect to the center of gravity; and

3. The area or size of the tail surfaces.

In analyzing stability, it should be recalled that abody that is free to rotate will always turn about itscenter of gravity.

To obtain static longitudinal stability, the relation ofthe wing and tail moments must be such that, if themoments are initially balanced and the airplane issuddenly nosed up, the wing moments and tailmoments will change so that the sum of their forceswill provide an unbalanced but restoring momentwhich, in turn, will bring the nose down again.Similarly, if the airplane is nosed down, the resultingchange in moments will bring the nose back up.

The center of lift, sometimes called the center ofpressure, in most unsymmetrical airfoils has a ten-dency to change its fore and aft position with achange in the angle of attack. The center of pressuretends to move forward with an increase in angle ofattack and to move aft with a decrease in angle ofattack. This means that when the angle of attack ofan airfoil is increased, the center of pressure (lift) bymoving forward, tends to lift the leading edge of thewing still more. This tendency gives the wing aninherent quality of instability.

Figure 3-12 shows an airplane in straight-and-levelflight. The line CG-CL-T represents the airplane’slongitudinal axis from the center of gravity (CG) toa point T on the horizontal stabilizer. The center oflift (or center of pressure) is represented by thepoint CL.

Most airplanes are designed so that the wing’s centerof lift (CL) is to the rear of the center of gravity. Thismakes the airplane “nose heavy” and requires thatthere be a slight downward force on the horizontalstabilizer in order to balance the airplane and keep

the nose from continually pitching downward.Compensation for this nose heaviness is providedby setting the horizontal stabilizer at a slight neg-ative angle of attack. The downward force thusproduced, holds the tail down, counterbalancingthe “heavy” nose. It is as if the line CG-CL-T wasa lever with an upward force at CL and two down-ward forces balancing each other, one a strongforce at the CG point and the other, a much lesserforce, at point T (downward air pressure on thestabilizer). Applying simple physics principles, itcan be seen that if an iron bar were suspended atpoint CL with a heavy weight hanging on it at theCG, it would take some downward pressure atpoint T to keep the “lever” in balance.

Even though the horizontal stabilizer may be levelwhen the airplane is in level flight, there is adownwash of air from the wings. This downwashstrikes the top of the stabilizer and produces adownward pressure, which at a certain speed willbe just enough to balance the “lever.” The fasterthe airplane is flying, the greater this downwashand the greater the downward force on the horizontalstabilizer (except “T” tails). [Figure 3-13] In air-planes with fixed position horizontal stabilizers, theairplane manufacturer sets the stabilizer at an anglethat will provide the best stability (or balance)during flight at the design cruising speed andpower setting. [Figure 3-14]

If the airplane’s speed decreases, the speed of the air-flow over the wing is decreased. As a result of thisdecreased flow of air over the wing, the downwashis reduced, causing a lesser downward force on thehorizontal stabilizer. In turn, the characteristic noseheaviness is accentuated, causing the airplane’s noseto pitch down more. This places the airplane in anose-low attitude, lessening the wing’s angle ofattack and drag and allowing the airspeed toincrease. As the airplane continues in the nose-lowattitude and its speed increases, the downward forceon the horizontal stabilizer is once again increased.

CL

CG

CLCG

T

T

Figure 3-12. Longitudinal stability.

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Consequently, the tail is again pushed downward andthe nose rises into a climbing attitude.

As this climb continues, the airspeed again decreases,causing the downward force on the tail to decreaseuntil the nose lowers once more. However, becausethe airplane is dynamically stable, the nose does notlower as far this time as it did before. The airplanewill acquire enough speed in this more gradual diveto start it into another climb, but the climb is not sosteep as the preceding one.

After several of these diminishing oscillations, inwhich the nose alternately rises and lowers, the air-plane will finally settle down to a speed at whichthe downward force on the tail exactly counteractsthe tendency of the airplane to dive. When thiscondition is attained, the airplane will once again

be in balanced flight and will continue in stabi-lized flight as long as this attitude and airspeed arenot changed.

A similar effect will be noted upon closing thethrottle. The downwash of the wings is reducedand the force at T in figure 3-12 is not enough tohold the horizontal stabilizer down. It is as if theforce at T on the lever were allowing the force ofgravity to pull the nose down. This, of course, is adesirable characteristic because the airplane isinherently trying to regain airspeed and reestablishthe proper balance.

Power or thrust can also have a destabilizing effectin that an increase of power may tend to make thenose rise. The airplane designer can offset this byestablishing a “high thrustline” wherein the line ofthrust passes above the center of gravity. [Figures3-15 and 3-16] In this case, as power or thrust isincreased a moment is produced to counteract thedown load on the tail. On the other hand, a very“low thrust line” would tend to add to the nose-upeffect of the horizontal tail surface.

Figure 3-15.Thrust line affects longitudinal stability.

It can be concluded, then, that with the center of gravityforward of the center of lift, and with an aerodynamictail-down force, the result is that the airplane alwaystries to return to a safe flying attitude.

A simple demonstration of longitudinal stability maybe made as follows: Trim the airplane for “hands off”control in level flight. Then momentarily give thecontrols a slight push to nose the airplane down. If,

Cruise Speed

High Speed

BalancedTail Load

LesserDownwardTail Load

GreaterDownwardTail Load

Low Speed

CG

CG

CG

Figure 3-13. Effect of speed on downwash.

Figure 3-14. Reduced power allows pitch down.

L

T

W

W

T

L

Normal Downwash

Reduced Downwash

T

Below CG

CG

TCG

Through CG

CGT

Above CG

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within a brief period, the nose rises to the originalposition and then stops, the airplane is staticallystable. Ordinarily, the nose will pass the originalposition (that of level flight) and a series of slowpitching oscillations will follow. If the oscillationsgradually cease, the airplane has positive stability;if they continue unevenly, the airplane has neutralstability; if they increase, the airplane is unstable.

LATERAL STABILITY (ROLLING)Stability about the airplane’s longitudinal axis,which extends from nose to tail, is called lateralstability. This helps to stabilize the lateral orrolling effect when one wing gets lower than thewing on the opposite side of the airplane. There arefour main design factors that make an airplane sta-ble laterally: dihedral, keel effect, sweepback, andweight distribution.

The most common procedure for producing lateralstability is to build the wings with a dihedral anglevarying from one to three degrees. In other words, thewings on either side of the airplane join the fuselageto form a slight V or angle called “dihedral,” and thisis measured by the angle made by each wing above aline parallel to the lateral axis.

The basis of rolling stability is, of course, the lat-eral balance of forces produced by the airplane’swings. Any imbalance in lift results in a tendencyfor the airplane to roll about its longitudinal axis.Stated another way, dihedral involves a balance of

lift created by the wings’ angle of attack on eachside of the airplane’s longitudinal axis.

If a momentary gust of wind forces one wing of theairplane to rise and the other to lower, the airplanewill bank. When the airplane is banked without turn-ing, it tends to sideslip or slide downward toward thelowered wing. [Figure 3-17] Since the wings havedihedral, the air strikes the low wing at much greaterangle of attack than the high wing. This increases thelift on the low wing and decreases lift on the highwing, and tends to restore the airplane to its originallateral attitude (wings level)—that is, the angle ofattack and lift on the two wings are again equal.

Figure 3-17. Dihedral for lateral stability.

The effect of dihedral, then, is to produce a rollingmoment tending to return the airplane to a laterallybalanced flight condition when a sideslip occurs.

The restoring force may move the low wing up toofar, so that the opposite wing now goes down. If so,the process will be repeated, decreasing with eachlateral oscillation until a balance for wings-levelflight is finally reached.

Conversely, excessive dihedral has an adverse effecton lateral maneuvering qualities. The airplane may beso stable laterally that it resists any intentional rollingmotion. For this reason, airplanes that require fast rollor banking characteristics usually have less dihedralthan those designed for less maneuverability.

The contribution of sweepback to dihedral effect isimportant because of the nature of the contribution.In a sideslip, the wing into the wind is operating withan effective decrease in sweepback, while the wingout of the wind is operating with an effective increasein sweepback. The swept wing is responsive only tothe wind component that is perpendicular to thewing’s leading edge. Consequently, if the wing is

T

L

CG

Cruise Power

L

CGT

Idle Power

L

CGT

Full Power

Figure 3-16. Power changes affect longitudinal stability.

Normal Angleof Attack

Normal Angleof Attack

Lesser Angleof Attack

Greater Angleof Attack

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operating at a positive lift coefficient, the wing intothe wind has an increase in lift, and the wing out ofthe wind has a decrease in lift. In this manner, theswept back wing would contribute a positive dihedraleffect and the swept forward wing would contribute anegative dihedral effect.

During flight, the side area of the airplane’s fuselageand vertical fin react to the airflow in much the samemanner as the keel of a ship. That is, it exerts asteadying influence on the airplane laterally aboutthe longitudinal axis.

Such laterally stable airplanes are constructed so thatthe greater portion of the keel area is above andbehind the center of gravity. [Figure 3-18] Thus,when the airplane slips to one side, the combinationof the airplane’s weight and the pressure of the air-flow against the upper portion of the keel area (bothacting about the CG) tends to roll the airplane backto wings-level flight.

Figure 3-18. Keel area for lateral stability.

VERTICAL STABILITY (YAWING)Stability about the airplane’s vertical axis (the side-ways moment) is called yawing or directional stability.

Yawing or directional stability is the more easilyachieved stability in airplane design. The area of thevertical fin and the sides of the fuselage aft of thecenter of gravity are the prime contributors whichmake the airplane act like the well known weather-vane or arrow, pointing its nose into the relativewind.

In examining a weathervane, it can be seen that ifexactly the same amount of surface were exposedto the wind in front of the pivot point as behind it,the forces fore and aft would be in balance andlittle or no directional movement would result.Consequently, it is necessary to have a greatersurface aft of the pivot point that forward of it.

Similarly in an airplane, the designer must ensurepositive directional stability by making the sidesurface greater aft than ahead of the center ofgravity. [Figure 3-19] To provide more positivestability aside from that provided by the fuselage,a vertical fin is added. The fin acts similar to thefeather on an arrow in maintaining straight flight.Like the weathervane and the arrow, the farther aftthis fin is placed and the larger its size, the greaterthe airplane’s directional stability.

Figure 3-19. Fuselage and fin for vertical stability.

If an airplane is flying in a straight line, and a side-ward gust of air gives the airplane a slight rotationabout its vertical axis (i.e., the right), the motion isretarded and stopped by the fin because while theairplane is rotating to the right, the air is striking theleft side of the fin at an angle. This causes pressureon the left side of the fin, which resists the turningmotion and slows down the airplane’s yaw. In doingso, it acts somewhat like the weathervane by turningthe airplane into the relative wind. The initial changein direction of the airplane’s flightpath is generallyslightly behind its change of heading. Therefore,after a slight yawing of the airplane to the right, thereis a brief moment when the airplane is still movingalong its original path, but its longitudinal axis ispointed slightly to the right.

The airplane is then momentarily skidding sideways,and during that moment (since it is assumed thatalthough the yawing motion has stopped, the excesspressure on the left side of the fin still persists) there

CG

CG

Centerline

Centerline

CG

AreaForwardof CG

Area AFTof CG

CG

Relative Wind Yaw

Yaw

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is necessarily a tendency for the airplane to be turnedpartially back to the left. That is, there is a momen-tary restoring tendency caused by the fin.

This restoring tendency is relatively slow in develop-ing and ceases when the airplane stops skidding. Whenit ceases, the airplane will be flying in a directionslightly different from the original direction. Inother words, it will not of its own accord return tothe original heading; the pilot must reestablish theinitial heading.

A minor improvement of directional stability maybe obtained through sweepback. Sweepback is incor-porated in the design of the wing primarily to delaythe onset of compressibility during high-speed flight.In lighter and slower airplanes, sweepback aidsin locating the center of pressure in the correctrelationship with the center of gravity. A longitudinallystable airplane is built with the center of pressure aft ofthe center of gravity.

Because of structural reasons, airplane designerssometimes cannot attach the wings to the fuselage atthe exact desired point. If they had to mount thewings too far forward, and at right angles to thefuselage, the center of pressure would not be farenough to the rear to result in the desired amount oflongitudinal stability. By building sweepback intothe wings, however, the designers can move the cen-ter of pressure toward the rear. The amount ofsweepback and the position of the wings then placethe center of pressure in the correct location.

The contribution of the wing to static directional sta-bility is usually small. The swept wing provides astable contribution depending on the amount ofsweepback, but the contribution is relatively smallwhen compared with other components.

FREE DIRECTIONAL OSCILLATIONS (DUTCH ROLL)Dutch Roll is a coupled lateral/directional oscillationthat is usually dynamically stable but is objectionablein an airplane because of the oscillatory nature. Thedamping of the oscillatory mode may be weak orstrong depending on the properties of the particularairplane.

Unfortunately all air is not smooth. There are bumpsand depressions created by gusty updrafts and down-drafts, and by gusts from ahead, behind, or the sideof the airplane.

The response of the airplane to a disturbance fromequilibrium is a combined rolling/yawing oscillationin which the rolling motion is phased to precedethe yawing motion. The yawing motion is not too

significant, but the roll is much more noticeable.When the airplane rolls back toward level flight inresponse to dihedral effect, it rolls back too farand sideslips the other way. Thus, the airplaneovershoots each time because of the strong dihe-dral effect. When the dihedral effect is large incomparison with static directional stability, theDutch Roll motion has weak damping and isobjectionable. When the static directional stabilityis strong in comparison with the dihedral effect,the Dutch Roll motion has such heavy dampingthat it is not objectionable. However, these qualitiestend toward spiral instability.

The choice is then the least of two evils—Dutch Rollis objectionable and spiral instability is tolerable ifthe rate of divergence is low. Since the moreimportant handling qualities are a result of highstatic directional stability and minimum necessarydihedral effect, most airplanes demonstrate a mildspiral tendency. This tendency would be indicatedto the pilot by the fact that the airplane cannot beflown “hands off” indefinitely.

In most modern airplanes, except high-speedswept wing designs, these free directional oscilla-tions usually die out automatically in a very fewcycles unless the air continues to be gusty orturbulent. Those airplanes with continuing DutchRoll tendencies usually are equipped with gyrostabilized yaw dampers. An airplane that hasDutch Roll tendencies is disconcerting, to say theleast. Therefore, the manufacturer tries to reach amedium between too much and too little direc-tional stability. Because it is more desirable forthe airplane to have “spiral instability” than DutchRoll tendencies, most airplanes are designed withthat characteristic.

SPIRAL INSTABILITYSpiral instability exists when the static directionalstability of the airplane is very strong as comparedto the effect of its dihedral in maintaining lateralequilibrium. When the lateral equilibrium of theairplane is disturbed by a gust of air and a sideslipis introduced, the strong directional stability tendsto yaw the nose into the resultant relative windwhile the comparatively weak dihedral lags inrestoring the lateral balance. Due to this yaw, thewing on the outside of the turning moment travelsforward faster than the inside wing and as a conse-quence, its lift becomes greater. This produces anoverbanking tendency which, if not corrected bythe pilot, will result in the bank angle becomingsteeper and steeper. At the same time, the strongdirectional stability that yaws the airplane into therelative wind is actually forcing the nose to a lowerpitch attitude. Then, the start of a slow downward

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spiral which has begun, if not counteracted by thepilot, will gradually increase into a steep spiral dive.Usually the rate of divergence in the spiral motion isso gradual that the pilot can control the tendencywithout any difficulty.

All airplanes are affected to some degree by thischaracteristic although they may be inherently stablein all other normal parameters. This tendency wouldbe indicated to the pilot by the fact that the airplanecannot be flown “hands off” indefinitely.

Much study and effort has gone into developmentof control devices (wing leveler) to eliminate or atleast correct this instability. Advanced stages ofthis spiral condition demand that the pilot be verycareful in application of recovery controls, orexcessive loads on the structure may be imposed.Of the in-flight structural failures that haveoccurred in general aviation airplanes, improperrecovery from this condition has probably beenthe underlying cause of more fatalities than anyother single factor. The reason is that the airspeedin the spiral condition builds up rapidly, and theapplication of back elevator force to reduce thisspeed and to pull the nose up only “tightens theturn,” increasing the load factor. The results of theprolonged uncontrolled spiral are always thesame; either in-flight structural failure, crashinginto the ground, or both. The most common causeson record for getting into this situation are: loss ofhorizon reference, inability of the pilot to controlthe airplane by reference to instruments, or a com-bination of both.

AERODYNAMIC FORCES IN FLIGHT MANEUVERS

FORCES INTURNSIf an airplanewere viewed ins t r a i g h t - a n d -level flight fromthe rear [figure3-20], and if theforces acting onthe airplane actu-ally could beseen, two forces(lift and weight)

would be apparent, and if the airplane were in a bank itwould be apparent that lift did not act directly oppositeto the weight—it now acts in the direction of the bank.The fact that when the airplane banks, lift acts inwardtoward the center of the turn, as well as upward, is oneof the basic truths to remember in the consideration ofturns.

An object at rest or moving in a straight line willremain at rest or continue to move in a straight lineuntil acted on by some other force. An airplane, likeany moving object, requires a sideward force tomake it turn. In a normal turn, this force is suppliedby banking the airplane so that lift is exerted inwardas well as upward. The force of lift during a turn isseparated into two components at right angles toeach other. One component, which acts verticallyand opposite to the weight (gravity), is called the“vertical component of lift.” The other, which actshorizontally toward the center of the turn, is calledthe “horizontal component of lift,” or centripetalforce. The horizontal component of lift is the forcethat pulls the airplane from a straight flightpath tomake it turn. Centrifugal force is the “equal andopposite reaction” of the airplane to the change indirection and acts equal and opposite to the hori-zontal component of lift. This explains why, in acorrectly executed turn, the force that turns theairplane is not supplied by the rudder.

An airplane is not steered like a boat or an automo-bile; in order for it to turn, it must be banked. If theairplane is not banked, there is no force available thatwill cause it to deviate from a straight flightpath.Conversely, when an airplane is banked, it will turn,provided it is not slipping to the inside of the turn.Good directional control is based on the fact that theairplane will attempt to turn whenever it is banked.

Centripetal Force – The force opposite centrifugal force and attracts abody towards its axis of rotation.

Centrifugal Force—An apparent force resulting from the effect of iner-tia during a turn.

Figure 3-20. Forces during normal coordinated turn.

Lift

Weight

Level Flight

TotalLift

HorizontalComponent

VerticalComponent

CentrifugalForce

Weight ResultantLoad

Medium Banked Turn

TotalLift

VerticalComponent

HorizontalComponent

Weight

CentrifugalForce

ResultantLoad

Steep Banked Turn

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This fact should be borne in mind at all times, partic-ularly while attempting to hold the airplane instraight-and-level flight.

Merely banking the airplane into a turn produces nochange in the total amount of lift developed.However, as was pointed out, the lift during the bankis divided into two components: one vertical and theother horizontal. This division reduces the amount oflift which is opposing gravity and actually support-ing the airplane’s weight; consequently, the airplaneloses altitude unless additional lift is created. This isdone by increasing the angle of attack until the verti-cal component of lift is again equal to the weight.Since the vertical component of lift decreases as thebank angle increases, the angle of attack must beprogressively increased to produce sufficient verti-cal lift to support the airplane’s weight. The fact thatthe vertical component of lift must be equal to theweight to maintain altitude is an important fact toremember when making constant altitude turns.

At a given airspeed, the rate at which an airplaneturns depends upon the magnitude of the horizontalcomponent of lift. It will be found that the horizontalcomponent of lift is proportional to the angle ofbank—that is, it increases or decreases respectivelyas the angle of bank increases or decreases. It logi-cally follows then, that as the angle of bank isincreased the horizontal component of lift increases,thereby increasing the rate of turn. Consequently, atany given airspeed the rate of turn can be controlledby adjusting the angle of bank.

To provide a vertical component of lift sufficient tohold altitude in a level turn, an increase in the angleof attack is required. Since the drag of the airfoil isdirectly proportional to its angle of attack, induceddrag will increase as the lift is increased. This, inturn, causes a loss of airspeed in proportion to the

angle of bank; a small angle of bank results in asmall reduction in airspeed and a large angle ofbank results in a large reduction in airspeed.Additional thrust (power) must be applied to pre-vent a reduction in airspeed in level turns; therequired amount of additional thrust is proportionalto the angle of bank.

To compensate for added lift, which would result ifthe airspeed were increased during a turn, the angleof attack must be decreased, or the angle of bankincreased, if a constant altitude were to be main-tained. If the angle of bank were held constant andthe angle of attack decreased, the rate of turn woulddecrease. Therefore, in order to maintain a constantrate of turn as the airspeed is increased, the angle ofattack must remain constant and the angle of bankincreased.

It must be remembered that an increase in airspeedresults in an increase of the turn radius and that cen-trifugal force is directly proportional to the radius ofthe turn. In a correctly executed turn, the horizontalcomponent of lift must be exactly equal and oppositeto the centrifugal force. Therefore, as the airspeed isincreased in a constant rate level turn, the radius ofthe turn increases. This increase in the radius of turncauses an increase in the centrifugal force, whichmust be balanced by an increase in the horizontalcomponent of lift, which can only be increased byincreasing the angle of bank.

In a slipping turn, the airplane is not turning at therate appropriate to the bank being used, since the air-plane is yawed toward the outside of the turningflightpath. The airplane is banked too much for therate of turn, so the horizontal lift component isgreater than the centrifugal force. [Figure 3-21]Equilibrium between the horizontal lift componentand centrifugal force is reestablished either by

Figure 3-21. Normal, sloping, and skidding turns.

Lift Vertical Lift

HorizontalLift

CentrifugalForce

Weight Load

1. Normal Turn: Centrifugal Force Equals Horizontal Lift.

Weight Load

CentrifugalForce

Lift Vertical Lift

HorizontalLift

2. Slipping Turn: Centrifugal Force Less Than Horizontal Lift.

Vertical Lift

CentrifugalForce

LoadWeight

Lift

HorizontalLift

3. Skidding Turn: Centrifugal Force Greater Than Horizontal Lift.

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decreasing the bank, increasing the rate of turn, or acombination of the two changes.

A skidding turn results from an excess of centrifugalforce over the horizontal lift component, pulling theairplane toward the outside of the turn. The rate ofturn is too great for the angle of bank. Correction ofa skidding turn thus involves a reduction in the rateof turn, an increase in bank, or a combination of thetwo changes.

To maintain a given rate of turn, the angle of bankmust be varied with the airspeed. This becomes par-ticularly important in high-speed airplanes. Forinstance, at 400 miles per hour (m.p.h.), an airplanemust be banked approximately 44° to execute astandard rate turn (3° per second). At this angle ofbank, only about 79 percent of the lift of the airplanecomprises the vertical component of the lift; theresult is a loss of altitude unless the angle of attackis increased sufficiently to compensate for the lossof vertical lift.

FORCES IN CLIMBSFor all practical purposes, the wing’s lift in asteady state normal climb is the same as it is in asteady level flight at the same airspeed. Though theairplane’s flightpath has changed when the climbhas been established, the angle of attack of thewing with respect to the inclined flightpath revertsto practically the same values, as does the lift.There is an initial momentary change, however, asshown in figure 3-22. During the transition fromstraight-and-level flight to a climb, a change in liftoccurs when back elevator pressure is first applied.Raising the airplane’s nose increases the angle ofattack and momentarily increases the lift. Lift atthis moment is now greater than weight and startsthe airplane climbing. After the flightpath is stabi-lized on the upward incline, the angle of attack andlift again revert to about the level flight values.

If the climb is entered with no change in power set-ting, the airspeed gradually diminishes because the

thrust required to maintain a given airspeed in levelflight is insufficient to maintain the same airspeedin a climb. When the flightpath is inclined upward,a component of the airplane’s weight acts in thesame direction as, and parallel to, the total drag ofthe airplane, thereby increasing the total effectivedrag. Consequently, the total drag is greater than thepower, and the airspeed decreases. The reduction inairspeed gradually results in a correspondingdecrease in drag until the total drag (including thecomponent of weight acting in the same direction)equals the thrust. [Figure 3-23] Due to momentum,the change in airspeed is gradual, varying consider-ably with differences in airplane size, weight, totaldrag, and other factors.

Figure 3-23. Changes in speed during climb entry.

Generally, the forces of thrust and drag, and liftand weight, again become balanced when the air-speed stabilizes but at a value lower than instraight-and-level flight at the same power setting.Since in a climb the airplane’s weight is not onlyacting downward but rearward along with drag,additional power is required to maintain the sameairspeed as in level flight. The amount of powerdepends on the angle of climb. When the climb isestablished so steep that there is insufficient poweravailable, a slower speed results. It will be seenthen that the amount of reserve power determinesthe climb performance of the airplane.

FORCES IN DESCENTSAs in climbs, the forces acting on the airplane gothrough definite changes when a descent is enteredfrom straight-and-level flight. The analysis here isthat of descending at the same power as used instraight-and-level flight.

When forward pressure is applied to the elevatorcontrol to start descending, or the airplane’s nose isallowed to pitch down, the angle of attack isdecreased and, as a result, the lift of the airfoil isreduced. This reduction in total lift and angle ofattack is momentary and occurs during the time the

L

Steady ClimbNormal Lift

L

Climb EntryIncreased Lift

L

Level FlightNormal Lift

Figure 3-22. Changes in lift during climb entry.

TL

WD

D D

T

T

L

L

W

WLevel Flight

Forces BalancedConstant Speed

Climb EntryDrag GreaterThan Thrust

Speed Slowing

Steady ClimbForces BalancedConstant Speed

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flightpath changes downward. The change to adownward flightpath is due to the lift momentarilybecoming less than the weight of the airplane as theangle of attack is reduced. This imbalance betweenlift and weight causes the airplane to follow adescending flightpath with respect to the horizontalflightpath of straight-and-level flight. When theflightpath is in a steady descent, the airfoil’s angleof attack again approaches the original value, andlift and weight will again become stabilized. Fromthe time the descent is started until it is stabilized,the airspeed will gradually increase. This is due to acomponent of weight now acting forward along theflightpath, similar to the manner it acted rearwardin a climb. The overall effect is that of increasedpower or thrust, which in turn causes the increasein airspeed associated with descending at the samepower as used in level flight.

To descend at the same airspeed as used in straight-and-level flight, obviously, the power must be reducedas the descent is entered. The component of weightacting forward along the flightpath will increase asthe angle of rate of descent increases and conversely,will decrease as the angle of rate of descentdecreases. Therefore, the amount of power reductionrequired for a descent at the same speed as cruisewill be determined by the steepness of the descent.

STALLSAn airplane will fly as long as the wing is creatingsufficient lift to counteract the load imposed on it.When the lift is completely lost, the airplane stalls.

Remember, the direct cause of every stall is anexcessive angle of attack. There are any number offlight maneuvers which may produce an increase inthe angle of attack, but the stall does not occur untilthe angle of attack becomes excessive.

It must be emphasized that the stalling speed of aparticular airplane is not a fixed value for all flightsituations. However, a given airplane will alwaysstall at the same angle of attack regardless of air-speed, weight, load factor, or density altitude. Eachairplane has a particular angle of attack where theairflow separates from the upper surface of the wingand the stall occurs. This critical angle of attackvaries from 16° to 20° depending on the airplane’sdesign. But each airplane has only one specific angleof attack where the stall occurs.

There are three situations in which the critical angleof attack can be exceeded: in low-speed flying, inhigh-speed flying, and in turning flight.

The airplane can be stalled in straight-and-levelflight by flying too slowly. As the airspeed is being

decreased, the angle of attack must be increased toretain the lift required for maintaining altitude. Theslower the airspeed becomes, the more the angle ofattack must be increased. Eventually, an angle ofattack is reached which will result in the wing notproducing enough lift to support the airplane and itwill start settling. If the airspeed is reduced further,the airplane will stall, since the angle of attack hasexceeded the critical angle and the airflow over thewing is disrupted.

It must be reemphasized here that low speed is notnecessary to produce a stall. The wing can bebrought into an excessive angle of attack at anyspeed. For example, take the case of an airplanewhich is in a dive with an airspeed of 200 knotswhen suddenly the pilot pulls back sharply on theelevator control. [Figure 3-24] Because of gravityand centrifugal force, the airplane could not immedi-ately alter its flightpath but would merely change itsangle of attack abruptly from quite low to very high.Since the flightpath of the airplane in relation to theoncoming air determines the direction of the relativewind, the angle of attack is suddenly increased, andthe airplane would quickly reach the stalling angle ata speed much greater than the normal stall speed.

Figure 3-24. Forces exerted when pulling out of a dive.

Similarly, the stalling speed of an airplane is higherin a level turn than in straight-and-level flight.[Figure 3-25] This is because centrifugal force isadded to the airplane’s weight, and the wing mustproduce sufficient additional lift to counterbalancethe load imposed by the combination of centrifugalforce and weight. In a turn, the necessary additionallift is acquired by applying back pressure to the ele-vator control. This increases the wing’s angle ofattack, and results in increased lift. The angle ofattack must increase as the bank angle increases tocounteract the increasing load caused by centrifugalforce. If at any time during a turn the angle of attackbecomes excessive, the airplane will stall.

L

CF

WL

L

CF

CF CF

W

WW

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At this point, the action of the airplane during astall should be examined. To balance the airplaneaerodynamically, the center of lift is normallylocated aft of the center of gravity. Although thismakes the airplane inherently “nose heavy,”downwash on the horizontal stabilizer counteractsthis condition. It can be seen then, that at the pointof stall when the upward force of the wing’s liftand the downward tail force cease, an unbalancedcondition exists. This allows the airplane to pitchdown abruptly, rotating about its center of gravity.During this nose-down attitude, the angle of attackdecreases and the airspeed again increases; hence,the smooth flow of air over the wing begins again,lift returns, and the airplane is again flying.However, considerable altitude may be lost beforethis cycle is complete.

BASIC PROPELLER PRINCIPLESThe airplane propeller consists of two or more bladesand a central hub to which the blades are attached.Each blade of an airplane propeller is essentially arotating wing. As a result of their construction, thepropeller blades are like airfoils and produce forcesthat create the thrust to pull, or push, the airplanethrough the air.

The power needed to rotate the propeller blades isfurnished by the engine. The engine rotates the air-foils of the blades through the air at high speeds, andthe propeller transforms the rotary power of theengine into forward thrust.

An airplane moving through the air creates a dragforce opposing its forward motion. Consequently, ifan airplane is to fly, there must be a force applied toit that is equal to the drag, but acting forward. Thisforce is called “thrust.”

A cross section of a typical propeller blade is shownin figure 3-26. This section or blade element is an

airfoil comparable to a cross section of an airplanewing. One surface of the blade is cambered orcurved, similar to the upper surface of an airplanewing, while the other surface is flat like the bottomsurface of a wing. The chord line is an imaginaryline drawn through the blade from its leading edgeto its trailing edge. As in a wing, the leading edge isthe thick edge of the blade that meets the air as thepropeller rotates.

Figure 3-26. Airfoil sections of propeller blade.

Blade angle, usually measured in degrees, is theangle between the chord of the blade and the planeof rotation [figure 3-27] and is measured at a spe-cific point along the length of the blade. Becausemost propellers have a flat blade “face,” the chordline is often drawn along the face of the propellerblade. Pitch is not the same as blade angle, butbecause pitch is largely determined by blade angle,the two terms are often used interchangeably. Anincrease or decrease in one is usually associated withan increase or decrease in the other.

Figure 3-27. Propeller blade angle.

The pitch of a propeller may be designated ininches. A propeller designated as a “74-48” wouldbe 74 inches in length and have an effective pitchof 48 inches. The pitch in inches is the distancewhich the propeller would screw through the air inone revolution if there were no slippage.

Figure 3-25. Increase in stall speed and load factor.

Stall Speed Increase

Load Factor

100

90

80

60

40

20

00 10 20 30 40 50 60 70 80 90

13121110987654321

Per

cent

Incr

ease

InS

tall

Spe

ed

Loa

d F

acto

r or

"G

"

Bank Angle, Degrees

Thrust

Angle of Attack

Chord

Line

Rel

ativ

e W

ind

Forward Velocity

Pitch orBlade Angle

Rot

atio

nal V

eloc

ity

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When specifying a fixed-pitch propeller for a newtype of airplane, the manufacturer usually selectsone with a pitch that will operate efficiently at theexpected cruising speed of the airplane.Unfortunately, however, every fixed-pitch propellermust be a compromise, because it can be efficient atonly a given combination of airspeed and r.p.m.Pilots do not have it within their power to changethis combination in flight.

When the airplane is at rest on the ground with theengine operating, or moving slowly at the beginningof takeoff, the propeller efficiency is very lowbecause the propeller is restrained from advancingwith sufficient speed to permit its fixed-pitch bladesto reach their full efficiency. In this situation, eachpropeller blade is turning through the air at an angleof attack that produces relatively little thrust for theamount of power required to turn it.

To understand the action of a propeller, consider firstits motion, which is both rotational and forward.Thus, as shown by the vectors of propeller forces infigure 3-27, each section of a propeller blade movesdownward and forward. The angle at which this air(relative wind) strikes the propeller blade is its angleof attack. The air deflection produced by this anglecauses the dynamic pressure at the engine side of thepropeller blade to be greater than atmospheric, thuscreating thrust.

The shape of the blade also creates thrust, becauseit is cambered like the airfoil shape of a wing.Consequently, as the air flows past the propeller, thepressure on one side is less than that on the other. As ina wing, this produces a reaction force in the directionof the lesser pressure. In the case of a wing, the airflowover the wing has less pressure, and the force (lift) isupward. In the case of the propeller, which is mountedin a vertical instead of a horizontal plane, the areaof decreased pressure is in front of the propeller,and the force (thrust) is in a forward direction.Aerodynamically, then, thrust is the result of thepropeller shape and the angle of attack of the blade.

Another way to consider thrust is in terms of themass of air handled by the propeller. In theseterms, thrust is equal to the mass of air handled,times the slipstream velocity, minus the velocityof the airplane. The power expended in producingthrust depends on the rate of air mass movement.On the average, thrust constitutes approximately80 percent of the torque (total horsepowerabsorbed by the propeller). The other 20 percent islost in friction and slippage. For any speed of rota-tion, the horsepower absorbed by the propellerbalances the horsepower delivered by the engine.For any single revolution of the propeller, the

amount of air handled depends on the blade angle,which determines how big a “bite” of air the pro-peller takes. Thus, the blade angle is an excellentmeans of adjusting the load on the propeller tocontrol the engine r.p.m.

The blade angle is also an excellent method ofadjusting the angle of attack of the propeller. On con-stant-speed propellers, the blade angle must beadjusted to provide the most efficient angle of attackat all engine and airplane speeds. Lift versus dragcurves, which are drawn for propellers as well aswings, indicate that the most efficient angle of attackis a small one varying from 2° to 4° positive. Theactual blade angle necessary to maintain this smallangle of attack varies with the forward speed of theairplane.

Fixed-pitch and ground-adjustable propellers aredesigned for best efficiency at one rotation and for-ward speed. They are designed for a given airplaneand engine combination. A propeller may be usedthat provides the maximum propeller efficiency foreither takeoff, climb, cruise, or high-speed flight.Any change in these conditions results in loweringthe efficiency of both the propeller and the engine.Since the efficiency of any machine is the ratio ofthe useful power output to the actual power input,propeller efficiency is the ratio of thrust horsepowerto brake horsepower. Propeller efficiency variesfrom 50 to 87 percent, depending on how much thepropeller “slips.”

Propeller slip is the difference between the geometricpitch of the propeller and its effective pitch.[Figure 3-28] Geometric pitch is the theoreticaldistance a propeller should advance in one revolu-tion; effective pitch is the distance it actuallyadvances. Thus, geometric or theoretical pitch isbased on no slippage, but actual or effective pitchincludes propeller slippage in the air.

Figure 3-28. Propeller slippage.

The reason a propeller is “twisted” is that the outerparts of the propeller blades, like all things that turnabout a central point, travel faster than the portionsnear the hub. [Figure 3-29] If the blades had the

Slip

Effective PitchGeometric Pitch

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same geometric pitch throughout their lengths, atcruise speed the portions near the hub could havenegative angles of attack while the propeller tipswould be stalled. “Twisting,” or variations in thegeometric pitch of the blades, permits the propellerto operate with a relatively constant angle of attackalong its length when in cruising flight. To put itanother way, propeller blades are twisted to changethe blade angle in proportion to the differences inspeed of rotation along the length of the propellerand thereby keep thrust more nearly equalized alongthis length.

Figure 3-29. Propeller tips travel faster than hubs.

Usually 1° to 4° provides the most efficient lift/dragratio, but in flight the propeller angle of attack of afixed-pitch propeller will vary—normally from 0° to15°. This variation is caused by changes in the rela-tive airstream which in turn results from changes inairplane speed. In short, propeller angle of attack isthe product of two motions: propeller rotation aboutits axis and its forward motion.

A constant-speed propeller, however, automaticallykeeps the blade angle adjusted for maximum effi-ciency for most conditions encountered in flight.During takeoff, when maximum power and thrustare required, the constant-speed propeller is at a lowpropeller blade angle or pitch. The low blade anglekeeps the angle of attack small and efficient withrespect to the relative wind. At the same time, itallows the propeller to handle a smaller mass of airper revolution. This light load allows the engine toturn at high r.p.m. and to convert the maximumamount of fuel into heat energy in a given time. The

high r.p.m. also creates maximum thrust; for,although the mass of air handled per revolution issmall, the number of revolutions per minute is many,the slipstream velocity is high, and with the low air-plane speed, the thrust is maximum.

After liftoff, as the speed of the airplane increases,the constant-speed propeller automatically changesto a higher angle (or pitch). Again, the higher bladeangle keeps the angle of attack small and efficientwith respect to the relative wind. The higher bladeangle increases the mass of air handled per revolu-tion. This decreases the engine r.p.m., reducing fuelconsumption and engine wear, and keeps thrust at amaximum.

After the takeoff climb is established in an airplanehaving a controllable-pitch propeller, the pilotreduces the power output of the engine to climbpower by first decreasing the manifold pressure andthen increasing the blade angle to lower the r.p.m.

At cruising altitude, when the airplane is in levelflight and less power is required than is used in take-off or climb, the pilot again reduces engine power byreducing the manifold pressure and then increasingthe blade angle to decrease the r.p.m. Again, this pro-vides a torque requirement to match the reducedengine power; for, although the mass of air handledper revolution is greater, it is more than offset by adecrease in slipstream velocity and an increase inairspeed. The angle of attack is still small becausethe blade angle has been increased with an increasein airspeed.

TORQUE AND P FACTORTo the pilot, “torque” (the left turning tendency ofthe airplane) is made up of four elements whichcause or produce a twisting or rotating motionaround at least one of the airplane’s three axes. Thesefour elements are:

1. Torque Reaction from Engine and Propeller.

2. Corkscrewing Effect of the Slipstream.

3. Gyroscopic Action of the Propeller.

4. Asymmetric Loading of the Propeller (P Factor).

TORQUE REACTIONTorque reaction involves Newton’s Third Law ofPhysics—for every action, there is an equal andopposite reaction. As applied to the airplane, thismeans that as the internal engine parts and propellerare revolving in one direction, an equal force is try-ing to rotate the airplane in the opposite direction.[Figure 3-30]

Mod

erat

e

Travel Distance – Moderate Speed

Sho

rt

Travel Distance

Slow Speed

Gre

ater Travel Distance – Very High Speed

2500 r.p.m.

2500 r.p.m.

2500 r.p.m

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Figure 3-30.Torque reaction.

When the airplane is airborne, this force is actingaround the longitudinal axis, tending to make the air-plane roll. To compensate for this, some of the olderairplanes are rigged in a manner to create more lifton the wing that is being forced downward. Themore modern airplanes are designed with the engineoffset to counteract this effect of torque.

NOTE—Most United States built aircraft enginesrotate the propeller clockwise, as viewed from thepilot’s seat. The discussion here is with reference tothose engines.

Generally, the compensating factors are permanentlyset so that they compensate for this force at cruisingspeed, since most of the airplane’s operating lift is atthat speed. However, aileron trim tabs permit furtheradjustment for other speeds.

When the airplane’s wheels are on the ground duringthe takeoff roll, an additional turning momentaround the vertical axis is induced by torque reac-tion. As the left side of the airplane is being forceddown by torque reaction, more weight is beingplaced on the left main landing gear. This results inmore ground friction, or drag, on the left tire than onthe right, causing a further turning moment to theleft. The magnitude of this moment is dependent onmany variables. Some of these variables are: (1) sizeand horsepower of engine, (2) size of propeller andthe r.p.m., (3) size of the airplane, and (4) conditionof the ground surface.

This yawing moment on the takeoff roll is correctedby the pilot’s proper use of the rudder or rudder trim.

CORKSCREW EFFECTThe high-speed rotation of an airplane propellergives a corkscrew or spiraling rotation to the slip-stream. At high propeller speeds and low forwardspeed (as in the takeoffs and approaches to power-on stalls), this spiraling rotation is very compactand exerts a strong sideward force on the airplane’svertical tail surface. [Figure 3-31]

When this spiraling slipstream strikes the vertical finon the left, it causes a left turning moment about theairplane’s vertical axis. The more compact the spiral,the more prominent this force is. As the forwardspeed increases, however, the spiral elongates andbecomes less effective.

The corkscrew flow of the slipstream also causes arolling moment around the longitudinal axis.

Note that this rolling moment caused by thecorkscrew flow of the slipstream is to the right, whilethe rolling moment caused by torque reaction is tothe left—in effect one may be counteracting theother. However, these forces vary greatly and it is upto the pilot to apply proper correction action by useof the flight controls at all times. These forces mustbe counteracted regardless of which is the mostprominent at the time.

GYROSCOPIC ACTIONBefore the gyroscopic effects of the propeller can beunderstood, it is necessary to understand the basicprinciple of a gyroscope.

All practical applications of the gyroscope are basedupon two fundamental properties of gyroscopicaction: rigidity in space and precession. The one ofinterest for this discussion is precession.

Precession is the resultant action, or deflection, of aspinning rotor when a deflecting force is applied toits rim. As can be seen in figure 3-32, when a force isapplied, the resulting force takes effect 90° ahead ofand in the direction of rotation.

The rotating propeller of an airplane makes a verygood gyroscope and thus has similar properties. Anytime a force is applied to deflect the propeller out ofits plane of rotation, the resulting force is 90° aheadof and in the direction of rotation and in the directionof application, causing a pitching moment, a yawingmoment, or a combination of the two dependingupon the point at which the force was applied.

Action

Reaction

Prop Rotation

Yaw

Slipstream

Force

Figure 3-31. Corkscrewing slipstream.

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This element of torque effect has always beenassociated with and considered more prominent intailwheel-type airplanes, and most often occurswhen the tail is being raised during the takeoff roll.[Figure 3-33] This change in pitch attitude has thesame effect as applying a force to the top of thepropeller’s plane of rotation. The resultant forceacting 90° ahead causes a yawing moment to theleft around the vertical axis. The magnitude of thismoment depends on several variables, one ofwhich is the abruptness with which the tail israised (amount of force applied). However, preces-sion, or gyroscopic action, occurs when a force isapplied to any point on the rim of the propeller’splane of rotation; the resultant force will still be90° from the point of application in the directionof rotation. Depending on where the force isapplied, the airplane is caused to yaw left or right,to pitch up or down, or a combination of pitchingand yawing.

It can be said that as a result of gyroscopic action—any yawing around the vertical axis results in apitching moment, and any pitching around the lateralaxis results in a yawing moment.

To correct for the effect of gyroscopic action, it isnecessary for the pilot to properly use elevator andrudder to prevent undesired pitching and yawing.

ASYMMETRIC LOADING (P FACTOR)When an airplane is flying with a high angle ofattack, the “bite” of the downward moving blade is

greater than the “bite” of the upward movingblade; thus moving the center of thrust to theright of the prop disc area—causing a yawingmoment toward the left around the vertical axis.That explanation is correct; however, to provethis phenomenon, it would be necessary to workwind vector problems on each blade, which getsquite involved when considering both the angleof attack of the airplane and the angle of attack ofeach blade.

This asymmetric loading is caused by the resultantvelocity, which is generated by the combination ofthe velocity of the propeller blade in its plane ofrotation and the velocity of the air passing horizon-tally through the propeller “disc.” With the airplanebeing flown at positive angles of attack, the right(viewed from the rear) or downswinging blade, ispassing through an area of resultant velocity whichis greater than that affecting the left or upswingingblade. Since the propeller blade is an airfoil,increased velocity means increased lift. Therefore,the downswinging blade having more “lift” tendsto pull (yaw) the airplane’s nose to the left.

Simply stated, when the airplane is flying at a highangle of attack, the downward moving blade has ahigher resultant velocity; therefore creating more liftthan the upward moving blade. [Figure 3-34] Thismight be easier to visualize if the propeller shaft was

mounted perpendicular to the ground (like ahelicopter). If there were no air movement atall, except that generated by the propelleritself, identical sections of each blade wouldhave the same airspeed. However, with air mov-ing horizontally across this vertically mountedpropeller, the blade proceeding forward into theflow of air will have a higher airspeed than theblade retreating with the airflow. Thus, the bladeproceeding into the horizontal airflow is creatingmore lift, or thrust, moving the center of thrusttoward that blade. Visualize ROTATING thevertically mounted propeller shaft to shallower

Resultant force90°

Yaw

Effective Force

AppliedForce

Figure 3-32. Gyroscopic precession.

AppliedForce

ResultantForce

Yaw

EffectiveForce

Figure 3-33. Raising tail produces gyroscopic precession.

Low Angleof Attack

Load OnUpward Moving

Prop Blade

Load OnDownward Moving

Prop Blade

High Angleof Attack

Load OnUpward Moving

Prop Blade

Load OnDownward Moving

Prop Blade

Figure 3-34. Asymmetrical loading of propeller (P-factor).

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angles relative to the moving air (as on an airplane).This unbalanced thrust then becomes proportion-ately smaller and continues getting smaller until itreaches the value of zero when the propeller shaft isexactly horizontal in relation to the moving air.

Each of these four elements of torque effects varyin values with changes in flight situations. In onephase of flight, one of these elements may be moreprominent than another; whereas, in another phaseof flight, another element may be more prominent.The relationship of these values to each other willvary with different airplanes—depending on theAIRFRAME, ENGINE, AND PROPELLER com-binations as well as other design features.

To maintain positive control of the airplane in allflight conditions, the pilot must apply the flight con-trols as necessary to compensate for these varyingvalues.

LOAD FACTORSThe preceding sections only briefly considered someof the practical points of the principles of flight. Tobecome a pilot, a detailed technical course in thescience of aerodynamics is not necessary. However,with responsibilities for the safety of passengers, thecompetent pilot must have a well-founded concept ofthe forces which act on the airplane, and the advanta-geous use of these forces, as well as the operatinglimitations of the particular airplane. Any forceapplied to an airplane to deflect its flight from astraight line produces a stress on its structure; theamount of this force is termed “load factor.”

A load factor is the ratio of the total airload acting onthe airplane to the gross weight of the airplane. Forexample, a load factor of 3 means that the total loadon an airplane’s structure is three times its grossweight. Load factors are usually expressed in termsof “G”—that is, a load factor of 3 may be spoken ofas 3 G’s, or a load factor of 4 as 4 G’s.

It is interesting to note that in subjecting an airplaneto 3 G’s in a pullup from a dive, one will be presseddown into the seat with a force equal to three timesthe person’s weight. Thus, an idea of the magnitudeof the load factor obtained in any maneuver can bedetermined by considering the degree to which oneis pressed down into the seat. Since the operatingspeed of modern airplanes has increased signifi-cantly, this effect has become so pronounced that itis a primary consideration in the design of thestructure for all airplanes.

With the structural design of airplanes planned towithstand only a certain amount of overload, a

knowledge of load factors has become essential forall pilots. Load factors are important to the pilot fortwo distinct reasons:

1. Because of the obviously dangerous overload thatis possible for a pilot to impose on the airplanestructures; and

2. Because an increased load factor increases thestalling speed and makes stalls possible at seem-ingly safe flight speeds.

LOAD FACTORS IN AIRPLANE DESIGNThe answer to the question “how strong should anairplane be” is determined largely by the use to whichthe airplane will be subjected. This is a difficult prob-lem, because the maximum possible loads are muchtoo high for use in efficient design. It is true that anypilot can make a very hard landing or an extremelysharp pullup from a dive, which would result inabnormal loads. However, such extremely abnormalloads must be dismissed somewhat if airplanes arebuilt that will take off quickly, land slowly, and carrya worthwhile payload.

The problem of load factors in airplane design thenreduces to that of determining the highest load fac-tors that can be expected in normal operation undervarious operational situations. These load factorsare called “limit load factors.” For reasons ofsafety, it is required that the airplane be designed towithstand these load factors without any structuraldamage. Although the Code of Federal Regulationsrequires that the airplane structure be capable ofsupporting one and one-half times these limit loadfactors without failure, it is accepted that parts ofthe airplane may bend or twist under these loadsand that some structural damage may occur.

This 1.5 value is called the “factor of safety” andprovides, to some extent, for loads higher than thoseexpected under normal and reasonable operation.However, this strength reserve is not somethingwhich pilots should willfully abuse; rather it is therefor their protection when they encounter unexpectedconditions.

The above considerations apply to all loading con-ditions, whether they be due to gusts, maneuvers, orlandings. The gust load factor requirements now ineffect are substantially the same as those that havebeen in existence for years. Hundreds of thousandsof operational hours have proven them adequate forsafety. Since the pilot has little control over gustload factors (except to reduce the airplane’s speedwhen rough air is encountered), the gust loadingrequirements are substantially the same for mostgeneral aviation type airplanes regardless of their

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operational use. Generally, the gust load factors con-trol the design of airplanes which are intended forstrictly nonacrobatic usage.

An entirely different situation exists in airplanedesign with maneuvering load factors. It is necessaryto discuss this matter separately with respect to: (1)Airplanes which are designed in accordance with theCategory System (i.e., Normal, Utility, Acrobatic);and (2) Airplanes of older design which were built torequirements which did not provide for operationalcategories.

Airplanes designed under the Category System arereadily identified by a placard in the cockpit, whichstates the operational category (or categories) inwhich the airplane is certificated. The maximum safeload factors (limit load factors) specified for air-planes in the various categories are as follows:

CATEGORY LIMIT LOADNormal1 3.8 to –1.52Utility (mild acrobatics, including spins) 4.4 to –1.76Acrobatic 6.0 to –3.0

1 For airplanes with gross weight of more than 4,000pounds, the limit load factor is reduced. To the limitloads given above, a safety factor of 50 percent isadded.

There is an upward graduation in load factor with theincreasing severity of maneuvers. The CategorySystem provides for obtaining the maximum utilityof an airplane. If normal operation alone is intended,the required load factor (and consequently theweight of the airplane) is less than if the airplane isto be employed in training or acrobatic maneuvers asthey result in higher maneuvering loads.

Airplanes that do not have the category placard aredesigns that were constructed under earlier engineer-ing requirements in which no operational restrictionswere specifically given to the pilots. For airplanes ofthis type (up to weights of about 4,000 pounds) therequired strength is comparable to present-day util-ity category airplanes, and the same types of opera-tion are permissible. For airplanes of this type over4,000 pounds, the load factors decrease with weightso that these airplanes should be regarded as beingcomparable to the normal category airplanesdesigned under the Category System, and theyshould be operated accordingly.

LOAD FACTORS IN STEEP TURNSIn a constant altitude, coordinated turn in any air-plane, the load factor is the result of two forces:centrifugal force and gravity. [Figure 3-35] For anygiven bank angle, the rate of turn varies with the

airspeed; the higher the speed, the slower the rate ofturn. This compensates for added centrifugal force,allowing the load factor to remain the same.

Figure 3-35.Two forces cause load factor during turns.

Figure 3-36 reveals an important fact about turns—that the load factor increases at a terrific rate after abank has reached 45° or 50°. The load factor forany airplane in a 60° bank is 2 G’s. The load factorin an 80° bank is 5.76 G’s. The wing must producelift equal to these load factors if altitude is to bemaintained.

Figure 3-36. Angle of bank changes load factor.

It should be noted how rapidly the line denoting loadfactor rises as it approaches the 90° bank line, whichit reaches only at infinity. The 90° banked, constantaltitude turn mathematically is not possible. True, anairplane may be banked to 90° but not in a coordi-nated turn; an airplane which can be held in a 90°

60°

Centrifugal Force 1.73 G's

Load Factor 2 G'sGra

vity

1G

Load Factor Chart

7

6

5

4

3

2

1

0 10 20 30 40 50 60 70 80 90Bank Angle - In Degrees

Load

Fac

tor

- G

Uni

ts

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banked slipping turn is capable of straight knife-edged flight. At slightly more than 80°, the loadfactor exceeds the limit of 6 G’s, the limit loadfactor of an acrobatic airplane.

For a coordinated, constant altitude turn, theapproximate maximum bank for the average generalaviation airplane is 60°. This bank and its resultantnecessary power setting reach the limit of this typeof airplane. An additional 10° bank will increase theload factor by approximately 1 G, bringing it closeto the yield point established for these airplanes.[Figure 3-36]

LOAD FACTORS AND STALLING SPEEDSAny airplane, within the limits of its structure, maybe stalled at any airspeed. When a sufficiently highangle of attack is imposed, the smooth flow of airover an airfoil breaks up and separates, producing anabrupt change of flight characteristics and a suddenloss of lift, which results in a stall.

A study of this effect has revealed that the airplane’sstalling speed increases in proportion to the squareroot of the load factor. This means that an airplanewith a normal unaccelerated stalling speed of 50knots can be stalled at 100 knots by inducing a loadfactor of 4 G’s. If it were possible for this airplane towithstand a load factor of 9, it could be stalled at aspeed of 150 knots. Therefore, a competent pilotshould be aware of the following:

• The danger of inadvertently stalling the airplaneby increasing the load factor, as in a steep turn orspiral; and

• That in intentionally stalling an airplane above itsdesign maneuvering speed, a tremendous loadfactor is imposed.

Reference to the charts in figures 3-36 and 3-37 willshow that by banking the airplane to just beyond 72°in a steep turn produces a load factor of 3, and thestalling speed is increased significantly. If this turn ismade in an airplane with a normal unacceleratedstalling speed of 45 knots, the airspeed must be keptabove 75 knots to prevent inducing a stall. A similareffect is experienced in a quick pullup, or anymaneuver producing load factors above 1 G. Thishas been the cause of accidents resulting from a sud-den, unexpected loss of control, particularly in asteep turn or abrupt application of the back elevatorcontrol near the ground.

Since the load factor squares as the stalling speeddoubles, it may be realized that tremendous loadsmay be imposed on structures by stalling an airplaneat relatively high airspeeds.

The maximum speed at which an airplane may bestalled safely is now determined for all new designs.This speed is called the “design maneuveringspeed” (VA) and is required to be entered in theFAA-approved Airplane Flight Manual or Pilot’sOperating Handbook (AFM/POH) of all recentlydesigned airplanes. For older general aviation air-planes, this speed will be approximately 1.7 timesthe normal stalling speed. Thus, an older airplanewhich normally stalls at 60 knots must never bestalled at above 102 knots (60 knots x 1.7 = 102knots). An airplane with a normal stalling speed of

Figure 3-37. Load factor changes stall speed.

40

50

60

70

80

100

120

150

Load Factor vs. Stall Speed

0

1

2

3

4

5

Rat

io o

f Acc

el. V

to

Una

ccel

erat

ed V

ss

"G" Load Accelerated Stall Speed

Una

ccel

erat

ed S

tall

Spe

ed

0 1 2 3 4 5 6 7 8 20 40 60 80 100 120 140 160 180 200 220 240 260

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60 knots will undergo, when stalled at 102 knots, aload factor equal to the square of the increase inspeed or 2.89 G’s (1.7 x 1.7 = 2.89 G’s). (The abovefigures are an approximation to be considered as aguide and are not the exact answers to any set ofproblems. The design maneuvering speed should bedetermined from the particular airplane’s operatinglimitations when provided by the manufacturer.)

Since the leverage in the control system varieswith different airplanes and some types employ“balanced” control surfaces while others do not,the pressure exerted by the pilot on the controlscannot be accepted as an index of the load factorsproduced in different airplanes. In most cases, loadfactors can be judged by the experienced pilot fromthe feel of seat pressure. They can also be meas-ured by an instrument called an “accelerometer,”but since this instrument is not common in generalaviation training airplanes, the development of theability to judge load factors from the feel of theireffect on the body is important. A knowledge ofthe principles outlined above is essential to thedevelopment of this ability to estimate load factors.

A thorough knowledge of load factors induced byvarying degrees of bank, and the significance ofdesign maneuvering speed (VA) will aid in the pre-vention of two of the most serious types of accidents:

1. Stalls from steep turns or excessive maneuveringnear the ground; and

2. Structural failures during acrobatics or other vio-lent maneuvers resulting from loss of control.

LOAD FACTORS AND FLIGHT MANEUVERSCritical load factors apply to all flight maneuversexcept unaccelerated straight flight where a loadfactor of 1 G is always present. Certain maneuversconsidered in this section are known to involve rel-atively high load factors.

TURNS—Increased load factors are a characteristicof all banked turns. As noted in the section on loadfactors in steep turns and particularly figures 3-36and 3-37, load factors become significant both toflight performance and to the load on wing structureas the bank increases beyond approximately 45°.

The yield factor of the average light plane is reached ata bank of approximately 70° to 75°, and the stallingspeed is increased by approximately one-half at a bankof approximately 63°.

STALLS—The normal stall entered from straightlevel flight, or an unaccelerated straight climb, willnot produce added load factors beyond the 1 G of

straight-and-level flight. As the stall occurs, how-ever, this load factor may be reduced toward zero,the factor at which nothing seems to have weight;and the pilot has the feeling of “floating free inspace.” In the event recovery is effected by snappingthe elevator control forward, negative load factors,those which impose a down load on the wings andraise the pilot from the seat, may be produced.

During the pullup following stall recovery, significantload factors sometimes are induced. Inadvertentlythese may be further increased during excessive div-ing (and consequently high airspeed) and abruptpullups to level flight. One usually leads to the other,thus increasing the load factor. Abrupt pullups at highdiving speeds may impose critical loads on airplanestructures and may produce recurrent or secondarystalls by increasing the angle of attack to that ofstalling.

As a generalization, a recovery from a stall madeby diving only to cruising or design maneuveringairspeed, with a gradual pullup as soon as the air-speed is safely above stalling, can be effected witha load factor not to exceed 2 or 2.5 G’s. A higherload factor should never be necessary unlessrecovery has been effected with the airplane’s nosenear or beyond the vertical attitude, or at extremelylow altitudes to avoid diving into the ground.

SPINS—Since a stabilized spin is not essentiallydifferent from a stall in any element other thanrotation, the same load factor considerations applyas those that apply to stall recovery. Since spinrecoveries usually are effected with the nose muchlower than is common in stall recoveries, higherairspeeds and consequently higher load factors areto be expected. The load factor in a proper spinrecovery will usually be found to be about 2.5 G’s.

The load factor during a spin will vary with the spincharacteristics of each airplane but is usually foundto be slightly above the 1 G of level flight. There aretwo reasons this is true:

1. The airspeed in a spin is very low, usually within2 knots of the unaccelerated stalling speeds; and

2. The airplane pivots, rather than turns, while it isin a spin.

HIGH-SPEED STALLS—The average light planeis not built to withstand the repeated application ofload factors common to high-speed stalls. The loadfactor necessary for these maneuvers produces astress on the wings and tail structure, which does notleave a reasonable margin of safety in most light air-planes.

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The only way this stall can be induced at an airspeedabove normal stalling involves the imposition of anadded load factor, which may be accomplished by asevere pull on the elevator control. A speed of 1.7times stalling speed (about 102 knots in a light air-plane with a stalling speed of 60 knots) will producea load factor of 3 G’s. Further, only a very narrowmargin for error can be allowed for acrobatics inlight airplanes. To illustrate how rapidly the loadfactor increases with airspeed, a high-speed stall at112 knots in the same airplane would produce a loadfactor of 4 G’s.

CHANDELLES AND LAZY EIGHTS—It wouldbe difficult to make a definite statement concerningload factors in these maneuvers as both involvesmooth, shallow dives and pullups. The load factorsincurred depend directly on the speed of the divesand the abruptness of the pullups.

Generally, the better the maneuver is performed, theless extreme will be the load factor induced. A chan-delle or lazy eight, in which the pullup produces aload factor greater than 2 G’s will not result in asgreat a gain in altitude, and in low-powered airplanesit may result in a net loss of altitude.

The smoothest pullup possible, with a moderateload factor, will deliver the greatest gain in altitudein a chandelle and will result in a better overallperformance in both chandelles and lazy eights.Further, it will be noted that recommended entryspeed for these maneuvers is generally near themanufacturer’s design maneuvering speed, therebyallowing maximum development of load factorswithout exceeding the load limits.

ROUGH AIR—All certificated airplanes aredesigned to withstand loads imposed by gusts ofconsiderable intensity. Gust load factors increasewith increasing airspeed and the strength used fordesign purposes usually corresponds to the highestlevel flight speed. In extremely rough air, as in thun-derstorms or frontal conditions, it is wise to reducethe speed to the design maneuvering speed.Regardless of the speed held, there may be gusts thatcan produce loads which exceed the load limits.

Most airplane flight manuals now include turbulentair penetration information. Operators of modernairplanes, capable of a wide range of speeds andaltitudes, are benefited by this added feature both incomfort and safety. In this connection, it is to benoted that the maximum “never-exceed” placarddive speeds are determined for smooth air only.High-speed dives or acrobatics involving speedabove the known maneuvering speed should neverbe practiced in rough or turbulent air.

In summary, it must be remembered that load factorsinduced by intentional acrobatics, abrupt pullupsfrom dives, high-speed stalls, and gusts at high air-speeds all place added stress on the entire structureof an airplane.

Stress on the structure involves forces on any part ofthe airplane. There is a tendency for the uninformedto think of load factors only in terms of their effecton spars and struts. Most structural failures due toexcess load factors involve rib structure within theleading and trailing edges of wings and tail group.The critical area of fabric-covered airplanes is thecovering about one-third of the chord aft on the topsurface of the wing.

The cumulative effect of such loads over a longperiod of time may tend to loosen and weaken vitalparts so that actual failure may occur later when theairplane is being operated in a normal manner.

VG DIAGRAMThe flight operating strength of an airplane is pre-sented on a graph whose horizontal scale is based onload factor. [Figure 3-38] The diagram is called a Vgdiagram—velocity versus “g” loads or load factor.Each airplane has its own Vg diagram which is validat a certain weight and altitude.

The lines of maximum lift capability (curved lines)are the first items of importance on the Vg diagram.The subject airplane in the illustration is capable ofdeveloping no more than one positive “g” at 62m.p.h., the wing level stall speed of the airplane.Since the maximum load factor varies with thesquare of the airspeed, the maximum positive liftcapability of this airplane is 2 “g” at 92 m.p.h., 3“g” at 112 m.p.h., 4.4 “g” at 137 m.p.h., and soforth. Any load factor above this line is unavailableaerodynamically; i.e., the subject airplane cannotfly above the line of maximum lift capability (itwill stall). Essentially the same situation exists fornegative lift flight with the exception that the speednecessary to produce a given negative load factor ishigher than that to produce the same positive loadfactor.

If the subject airplane is flown at a positive loadfactor greater than the positive limit load factor of4.4, structural damage will be possible. When theairplane is operated in this region, objectionablepermanent deformation of the primary structuremay take place and a high rate of fatigue damage isincurred. Operation above the limit load factormust be avoided in normal operation.

There are two other points of importance on the Vgdiagram. First, is the intersection of the positive limit

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load factor and the line of maximum positive liftcapability. The airspeed at this point is the minimumairspeed at which the limit load can be developedaerodynamically. Any airspeed greater than this pro-vides a positive lift capability sufficient to damagethe airplane; any airspeed less does not providepositive lift capability sufficient to cause damagefrom excessive flight loads. The usual term given tothis speed is “maneuvering speed,” since considerationof subsonic aerodynamics would predict minimumusable turn radius to occur at this condition. Themaneuver speed is a valuable reference point, since anairplane operating below this point cannot produce adamaging positive flight load. Any combination ofmaneuver and gust cannot create damage due to excessairload when the airplane is below the maneuverspeed.

Next, is the intersection of the negative limit loadfactor and line of maximum negative lift capability.Any airspeed greater than this provides a negativelift capability sufficient to damage the airplane; anyairspeed less does not provide negative lift capabil-ity sufficient to damage the airplane from excessiveflight loads.

The limit airspeed (or redline speed) is a design ref-erence point for the airplane—the subject airplane islimited to 225 m.p.h. If flight is attempted beyond

the limit airspeed, structural damage or structuralfailure may result from a variety of phenomena.

Thus, the airplane in flight is limited to a regime ofairspeeds and g’s which do not exceed the limit (orredline) speed, do not exceed the limit load factor,and cannot exceed the maximum lift capability. Theairplane must be operated within this “envelope” toprevent structural damage and ensure that the antic-ipated service lift of the airplane is obtained. Thepilot must appreciate the Vg diagram as describingthe allowable combination of airspeeds and loadfactors for safe operation. Any maneuver, gust, orgust plus maneuver outside the structural envelopecan cause structural damage and effectively shortenthe service life of the airplane.

WEIGHT AND BALANCEOften a pilot regards the airplane’s weight and balancedata as information of interest only to engineers,dispatchers, and operators of scheduled and non-scheduled air carriers. Along with this idea, thereasoning is that the airplane was weighed duringthe certification process and that this data is validindefinitely, regardless of equipment changes ormodifications. Further, this information is mistakenlyreduced to a workable routine or “rule of thumb”such as: “If I have three passengers, I can load only100 gallons of fuel; four passengers—70 gallons.”

Figure 3-38.Typical Vg diagram.

Structural Damage

Structural Damage

Caution Range

NormalStall Speed

Level Flight at One "G"

Accelerated Stall

NormalOperating

Range

Maneuvering Speed

Max.Structural

Cruise Speed

Structural

Failure

7

6

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3

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1

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-1

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-3

Load

Fac

tor

20 40 60 80 100 120 140 160 180 200 220 240

Indicated Airspeed MPH

Never ExceedSpeed

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Admittedly, this rule of thumb is adequate in manycases, but as the subject “Weight and Balance” sug-gests, the concern is not only with the weight of theairplane but also the location of its center of gravity(CG). The importance of the CG should have becomeapparent in the discussion of stability, controllability,and performance. If all pilots understood andrespected the effect of CG on an airplane, then onetype of accident would be eliminated from therecords: “PRIMARY CAUSE OF ACCIDENT—AIRPLANE CENTER OF GRAVITY OUT OFREARWARD LIMITS AND UNEQUAL LOADDISTRIBUTION RESULTING IN AN UNSTABLEAIRPLANE. PILOT LOST CONTROL OF AIR-PLANE ON TAKEOFF AND CRASHED.”

The reasons airplanes are so certificated are obviouswhen one gives it a little thought. For instance, it isof added value to the pilot to be able to carry extrafuel for extended flights when the full complementof passengers is not to be carried. Further, it is unrea-sonable to forbid the carriage of baggage when it isonly during spins that its weight will adversely affectthe airplane’s flight characteristics. Weight and bal-ance limits are placed on airplanes for two principalreasons:

1. Because of the effect of the weight on the air-plane’s primary structure and its performancecharacteristics; and

2. Because of the effect the location of this weighthas on flight characteristics, particularly in stalland spin recovery and stability.

EFFECTS OF WEIGHT ON FLIGHT PERFORMANCEThe takeoff/climb and landing performance of anairplane are determined on the basis of its maximumallowable takeoff and landing weights. A heaviergross weight will result in a longer takeoff run andshallower climb, and a faster touchdown speed andlonger landing roll. Even a minor overload maymake it impossible for the airplane to clear an obsta-cle that normally would not have been seriouslyconsidered during takeoffs under more favorableconditions.

The detrimental effects of overloading on performanceare not limited to the immediate hazards involvingtakeoffs and landings. Overloading has an adverseeffect on all climb and cruise performance which leadsto overheating during climbs, added wear on engineparts, increased fuel consumption, slower cruisingspeeds, and reduced range.

The manufacturers of modern airplanes furnishweight and balance data with each airplane produced.

Generally, this information may be found in the FAA-approved Airplane Flight Manual or Pilot’s OperatingHandbook (AFM/POH). With the advancements inairplane design and construction in recent years hascome the development of “easy to read charts” fordetermining weight and balance data. Increasedperformance and load carrying capability of theseairplanes require strict adherence to the operatinglimitations prescribed by the manufacturer.Deviations from the recommendations can result instructural damage or even complete failure of theairplane’s structure. Even if an airplane is loadedwell within the maximum weight limitations, it isimperative that weight distribution be within thelimits of center of gravity location. The precedingbrief study of aerodynamics and load factors pointsout the reasons for this precaution. The followingdiscussion is background information into some ofthe reasons why weight and balance conditions areimportant to the safe flight of an airplane.

The pilot is often completely unaware of the weightand balance limitations of the airplane being flownand of the reasons for these limitations. In some air-planes, it is not possible to fill all seats, baggagecompartments, and fuel tanks, and still remainwithin approved weight or balance limits. As anexample, in several popular four-place airplanes thefuel tanks may not be filled to capacity when fouroccupants and their baggage are carried. In a certaintwo-place airplane, no baggage may be carried inthe compartment aft of the seats when spins are tobe practiced.

EFFECT OF WEIGHT ON AIRPLANE STRUCTUREThe effect of additional weight on the wing structureof an airplane is not readily apparent. Airworthinessrequirements prescribe that the structure of an air-plane certificated in the normal category (in whichacrobatics are prohibited) must be strong enoughto withstand a load factor of 3.8 to take care ofdynamic loads caused by maneuvering and gusts.This means that the primary structure of the airplanecan withstand a load of 3.8 times the approved grossweight of the airplane without structural failureoccurring. If this is accepted as indicative of theload factors that may be imposed during operationsfor which the airplane is intended, a 100-poundoverload imposes a potential structural overloadof 380 pounds. The same consideration is evenmore impressive in the case of utility and acrobaticcategory airplanes, which have load factorrequirements of 4.4 and 6.0 respectively.

Structural failures which result from overloadingmay be dramatic and catastrophic, but more oftenthey affect structural components progressively in a

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manner which is difficult to detect and expensive torepair. One of the most serious results of habitualoverloading is that its results tend to be cumulative,and may result in structural failure later during com-pletely normal operations. The additional stressplaced on structural parts by overloading is believed toaccelerate the occurrence of metallic fatigue failures.

A knowledge of load factors imposed by flightmaneuvers and gusts will emphasize the conse-quences of an increase in the gross weight of anairplane. The structure of an airplane about toundergo a load factor of 3 G’s, as in the recoveryfrom a steep dive, must be prepared to withstandan added load of 300 pounds for each 100-poundincrease in weight. It should be noted that thiswould be imposed by the addition of about 16 gallonsof unneeded fuel in a particular airplane. The FAAcertificated civil airplane has been analyzed struc-turally, and tested for flight at the maximum grossweight authorized and within the speeds posted forthe type of flights to be performed. Flights at weightsin excess of this amount are quite possible and oftenare well within the performance capabilities of anairplane. Nonetheless, this fact should not beallowed to mislead the pilot, as the pilot may notrealize that loads for which the airplane was notdesigned are being imposed on all or some part ofthe structure.

In loading an airplane with either passengers orcargo, the structure must be considered. Seats,baggage compartments, and cabin floors aredesigned for a certain load or concentration ofload and no more. As an example, a light planebaggage compartment may be placarded for 20pounds because of the limited strength of its sup-porting structure even though the airplane may notbe overloaded or out of center-of-gravity limitswith more weight at that location.

EFFECTS OF WEIGHT ON STABILITY AND CONTROLLABILITYThe effects that overloading has on stability also arenot generally recognized. An airplane, which isobserved to be quite stable and controllable whenloaded normally, may be discovered to have verydifferent flight characteristics when it is overloaded.Although the distribution of weight has the mostdirect effect on this, an increase in the airplane’sgross weight may be expected to have an adverseeffect on stability, regardless of location of thecenter of gravity.

The stability of many certificated airplanes is com-pletely unsatisfactory if the gross weight isexceeded.

EFFECT OF LOAD DISTRIBUTIONThe effect of the position of the center of gravityon the load imposed on an airplane’s wing in flightis not generally realized, although it may be verysignificant to climb and cruising performance.Contrary to the beliefs of some pilots, an airplanewith forward loading is “heavier” and conse-quently, slower than the same airplane with thecenter of gravity further aft.

Figure 3-39 illustrates the reason for this. With forwardloading, “nose-up” trim is required in most airplanesto maintain level cruising flight. Nose-up triminvolves setting the tail surfaces to produce agreater down load on the aft portion of the fuselage,which adds to the wing loading and the total liftrequired from the wing if altitude is to be main-tained. This requires a higher angle of attack ofthe wing, which results in more drag and, in turn,produces a higher stalling speed.

Figure 3-39. Load distribution affects balance.

With aft loading and “nose-down” trim, the tail sur-faces will exert less down load, relieving the wing ofthat much wing loading and lift required to maintainaltitude. The required angle of attack of the wing isless, so the drag is less, allowing for a faster cruisespeed. Theoretically, a neutral load on the tail surfacesin cruising flight would produce the most efficientoverall performance and fastest cruising speed, butwould also result in instability. Consequently, modernairplanes are designed to require a down load on thetail for stability and controllability.

Remember that a zero indication on the trim tab con-trol is not necessarily the same as “neutral trim”because of the force exerted by downwash from thewings and the fuselage on the tail surfaces.

The effects of the distribution of the airplane’s use-ful load have a significant influence on its flight

Centerof Lift

Centerof Lift

Load Imposedby Tail

Gross Weight

ForwardCG

Load Imposedby TailGross Weight

AFT CG

StrongerDown Load

on Tail

LighterDown Load

on Tail

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characteristics, even when the load is within the cen-ter-of-gravity limits and the maximum permissiblegross weight. Important among these effects arechanges in controllability, stability, and the actualload imposed on the wing.

Generally, an airplane becomes less controllable,especially at slow flight speeds, as the center ofgravity is moved further aft. An airplane whichcleanly recovers from a prolonged spin with thecenter of gravity at one position may fail completelyto respond to normal recovery attempts when thecenter of gravity is moved aft by 1 or 2 inches.

It is common practice for airplane designers toestablish an aft center-of-gravity limit that is within1 inch of the maximum which will allow normalrecovery from a one-turn spin. When certificatingan airplane in the utility category to permit inten-tional spins, the aft center-of-gravity limit is usuallyestablished at a point several inches forward of thatwhich is permissible for certification in the normalcategory.

Another factor affecting controllability, which isbecoming more important in current designs of largeairplanes, is the effect of long moment arms to thepositions of heavy equipment and cargo. The sameairplane may be loaded to maximum gross weightwithin its center-of-gravity limits by concentratingfuel, passengers, and cargo near the design center ofgravity; or by dispersing fuel and cargo loads inwingtip tanks and cargo bins forward and aft of thecabin.

With the same total weight and center of gravity,maneuvering the airplane or maintaining level flightin turbulent air will require the application of greatercontrol forces when the load is dispersed. This is truebecause of the longer moment arms to the positions ofthe heavy fuel and cargo loads which must be over-come by the action of the control surfaces. An airplanewith full outboard wing tanks or tip tanks tends to besluggish in roll when control situations are marginal,while one with full nose and aft cargo bins tends to beless responsive to the elevator controls.

The rearward center-of-gravity limit of an airplane isdetermined largely by considerations of stability.The original airworthiness requirements for a typecertificate specify that an airplane in flight at a cer-tain speed will dampen out vertical displacementof the nose within a certain number of oscillations.An airplane loaded too far rearward may not dothis; instead when the nose is momentarily pulledup, it may alternately climb and dive becomingsteeper with each oscillation. This instability is notonly uncomfortable to occupants, but it could even

become dangerous by making the airplane unman-ageable under certain conditions.

The recovery from a stall in any airplane becomesprogressively more difficult as its center of gravitymoves aft. This is particularly important in spinrecovery, as there is a point in rearward loading ofany airplane at which a “flat” spin will develop. Aflat spin is one in which centrifugal force, actingthrough a center of gravity located well to the rear,will pull the tail of the airplane out away from theaxis of the spin, making it impossible to get the nosedown and recover.

An airplane loaded to the rear limit of its permissiblecenter-of-gravity range will handle differently inturns and stall maneuvers and have different landingcharacteristics than when it is loaded near the for-ward limit.

The forward center-of-gravity limit is determined bya number of considerations. As a safety measure, itis required that the trimming device, whether tab oradjustable stabilizer, be capable of holding the air-plane in a normal glide with the power off. A con-ventional airplane must be capable of a full stall,power-off landing in order to ensure minimum land-ing speed in emergencies. A tailwheel-type airplaneloaded excessively nose heavy will be difficult totaxi, particularly in high winds. It can be nosed overeasily by use of the brakes, and it will be difficult toland without bouncing since it tends to pitch downon the wheels as it is slowed down and flared forlanding. Steering difficulties on the ground mayoccur in nosewheel-type airplanes, particularly dur-ing the landing roll and takeoff.

• The CG position influences the lift and angle ofattack of the wing, the amount and direction offorce on the tail, and the degree of deflection ofthe stabilizer needed to supply the proper tailforce for equilibrium. The latter is very importantbecause of its relationship to elevator controlforce.

• The airplane will stall at a higher speed with aforward CG location. This is because the stallingangle of attack is reached at a higher speed due toincreased wing loading.

• Higher elevator control forces normally existwith a forward CG location due to the increasedstabilizer deflection required to balance the air-plane.

• The airplane will cruise faster with an aft CGlocation because of reduced drag. The drag isreduced because a smaller angle of attack and less

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downward deflection of the stabilizer arerequired to support the airplane and overcome thenose-down pitching tendency.

• The airplane becomes less stable as the CG ismoved rearward. This is because when the CG ismoved rearward it causes an increase in the angleof attack. Therefore, the wing contribution to theairplane’s stability is now decreased, while thetail contribution is still stabilizing. When thepoint is reached that the wing and tail contribu-tions balance, then neutral stability exists. AnyCG movement further aft will result in an unsta-ble airplane.

• A forward CG location increases the need forgreater back elevator pressure. The elevator mayno longer be able to oppose any increase innose-down pitching. Adequate elevator controlis needed to control the airplane throughout theairspeed range down to the stall.

HIGH-SPEED FLIGHT

SUPERSONIC VS. SUBSONIC FLOWIn subsonic aerodynamics, the theory of lift is basedupon the forces generated on a body and a movinggas (air) in which it is immersed. At speeds belowabout 260 knots, air can be considered incompress-ible, in that at a fixed altitude, its density remainsnearly constant while its pressure varies. Underthis assumption, air acts the same as water and isclassified as a fluid. Subsonic aerodynamic theoryalso assumes the effects of viscosity (the propertyof a fluid that tends to prevent motion of one partof the fluid with respect to another) are negligible,and classifies air as an ideal fluid, conforming tothe principles of ideal-fluid aerodynamics such ascontinuity, Bernoulli’s principle, and circulation.

In reality, air is compressible and viscous. While theeffects of these properties are negligible at lowspeeds, compressibility effects in particular becomeincreasingly important as speed increases.Compressibility (and to a lesser extent viscosity) isof paramount importance at speeds approaching thespeed of sound. In these speed ranges, compressibil-ity causes a change in the density of the air aroundan airplane.

During flight, a wing produces lift by acceleratingthe airflow over the upper surface. This acceleratedair can, and does, reach sonic speeds even though theairplane itself may be flying subsonic. At someextreme angles of attack, in some airplanes, thespeed of the air over the top surface of the wing maybe double the airplane’s speed. It is therefore entirely

possible to have both supersonic and subsonic air-flow on an airplane at the same time. When flowvelocities reach sonic speeds at some location on anairplane (such as the area of maximum camber onthe wing), further acceleration will result in theonset of compressibility effects such as shock waveformation, drag increase, buffeting, stability, andcontrol difficulties. Subsonic flow principles areinvalid at all speeds above this point. [Figure 3-40]

Figure 3-40. Wing airflow.

SPEED RANGESThe speed of sound varies with temperature. Understandard temperature conditions of 15°C, the speedof sound at sea level is 661 knots. At 40,000 feet,where the temperature is –55°C, the speed of sounddecreases to 574 knots. In high-speed flight and/orhigh-altitude flight, the measurement of speed isexpressed in terms of a “Mach number”—the ratioof the true airspeed of the airplane to the speed ofsound in the same atmospheric conditions. An air-plane traveling at the speed of sound is traveling atMach 1.0. Airplane speed regimes are defined asfollows:

Subsonic—Mach numbers below 0.75

Transonic—Mach numbers from .075 to 1.20

Supersonic—Mach numbers from 1.20 to 5.00

Hypersonic—Mach numbers above 5.00

While flights in the transonic and supersonic rangesare common occurrences for military airplanes,civilian jet airplanes normally operate in a cruisespeed range of Mach 0.78 to Mach 0.90.

The speed of an airplane in which airflow over anypart of the wing first reaches (but does not exceed)Mach 1.0 is termed that airplane’s critical Machnumber or “Mach Crit.” Thus, critical Mach number

M=.50

M=.72(Critical Mach Number)

SupersonicFlow

M=.77

Normal Shock WaveSubsonic Possible Separation

Maximum Local VelocityIs Less Than Sonic

Maximum Local VelocityEqual To Sonic

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is the boundary between subsonic and transonicflight and is an important point of reference for allcompressibility effects encountered in transonicflight. Shock waves, buffet, and airflow separationtake place above critical Mach number. A jet airplanetypically is most efficient when cruising at or near itscritical Mach number. At speeds 5 – 10 percent abovethe critical Mach number, compressibility effectsbegin. Drag begins to rise sharply. Associated withthe “drag rise” are buffet, trim and stability changes,and a decrease in control surface effectiveness. Thisis the point of “drag divergence,” and is typically thespeed chosen for high-speed cruise operations. Atsome point beyond high-speed cruise are the turbinepowered airplane’s maximum operating limitspeeds: VMO/MMO. [Figure 3-41]

Figure 3-41. Critical Mach.

VMO is the maximum operating speed expressed interms of knots. VMO limits ram air pressure actingagainst the structure and prevents flutter. MMO is themaximum operating speed expressed in terms of Machnumber. An airplane should not be flown in excess ofthis speed. Doing so risks encountering the full effectsof compressibility, including possible loss of control.

MACH NUMBER VS. AIRSPEEDSpeeds such as Mach Crit and MMO for a specific air-plane occur at a given Mach number. The true airspeed(TAS), however, varies with outside air temperature.Therefore, true airspeeds corresponding to a specificMach number can vary considerably (as much as 75 –100 knots). When an airplane cruising at a constantMach number enters an area of higher outside air tem-peratures, true airspeed and required fuel increases, andrange decreases. Conversely, when entering an area ofcolder outside air temperatures, true airspeed and fuelflow decreases, and range increases.

In a jet airplane operating at high altitude, the indicatedairspeed (IAS) for any given Mach number decreaseswith an increase in altitude above a certain level. Thereverse occurs during descent. Normally, climbs and

descents are accomplished using indicated airspeed inthe lower altitudes and Mach number in the higheraltitudes.

Unlike operations in the lower altitudes, the indi-cated airspeed (IAS) at which a jet airplane stallsincreases significantly with altitude. This is due tothe fact that true airspeed (TAS) increases withaltitude. At high true airspeeds, air compressioncauses airflow distortion over the wings and in thepitot system. At the same time, the indicated airspeed(IAS) representing MMO decreases with altitude.Eventually, the airplane can reach an altitude wherethere is little or no difference between the two.

BOUNDARY LAYERAir has viscosity, and will encounter resistance toflow over a surface. The viscous nature of airflowreduces the local velocities on a surface and isresponsible for skin friction drag. As the air passesover the wing’s surface, the air particles nearest thesurface come to rest. The next layer of particles isslowed down but not stopped. Some small but meas-urable distance from the surface, the air particles aremoving at free stream velocity. The layer of air overthe wing’s surface, which is slowed down or stoppedby viscosity, is termed the “boundary layer.” Typicalboundary layer thicknesses on an airplane rangefrom small fractions of an inch near the leading edgeof a wing to the order of 12 inches at the aft end of alarge airplane such as a Boeing 747.

There are two different types of boundary layer flow:laminar and turbulent. The laminar boundary layer is avery smooth flow, while the turbulent boundary layercontains swirls or “eddies.” The laminar flow createsless skin friction drag than the turbulent flow, but isless stable. Boundary layer flow over a wing surfacebegins as a smooth laminar flow. As the flow continuesback from the leading edge, the laminar boundary layerincreases in thickness. At some distance back from theleading edge, the smooth laminar flow breaks downand transitions to a turbulent flow. From a dragstandpoint, it is advisable to have the transition fromlaminar to turbulent flow as far aft on the wing aspossible, or have a large amount of the wing surfacewithin the laminar portion of the boundary layer. Thelow energy laminar flow, however, tends to breakdown more suddenly than the turbulent layer.

Another phenomenon associated with viscous flowis separation. Separation occurs when the airflowbreaks away from an airfoil. The natural progressionis from laminar boundary layer to turbulent bound-ary layer and then to airflow separation. Airflowseparation produces high drag and ultimatelydestroys lift. The boundary layer separation point

CDrag

Coefficient

DForce Divergence

Mach NumberCritical

Mach NumberC = 0.3L

0.5 1.0

M, Mach Number

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moves forward on the wing as the angle of attack isincreased. [Figure 3-42]

“Vortex Generators” are used to delay or preventshock wave induced boundary layer separationencountered in transonic flight. Vortex generatorsare small low aspect ratio airfoils placed at a 12° to15° angle of attack to the airstream. They are usu-ally spaced a few inches apart along the wingahead of the ailerons or other control surfaces.Vortex generators create a vortex which mixes theboundary airflow with the high energy airflow justabove the surface. This produces higher surfacevelocities and increases the energy of the boundarylayer. Thus, a stronger shock wave will be necessaryto produce airflow separation.

SHOCK WAVESWhen an airplane flies at subsonic speeds, the airahead is “warned” of the airplane’s coming by apressure change transmitted ahead of the airplane atthe speed of sound. Because of this warning, the airbegins to move aside before the airplane arrives andis prepared to let it pass easily. When the airplane’sspeed reaches the speed of sound, the pressurechange can no longer warn the air ahead because theairplane is keeping up with its own pressure waves.Rather, the air particles pile up in front of the air-plane causing a sharp decrease in the flow velocitydirectly in front of the airplane with a correspondingincrease in air pressure and density.

As the airplane’s speed increases beyond the speedof sound, the pressure and density of the compressedair ahead of it increase, the area of compressionextending some distance ahead of the airplane. Atsome point in the airstream, the air particles arecompletely undisturbed, having had no advancedwarning of the airplane’s approach, and in the nextinstant the same air particles are forced to undergosudden and drastic changes in temperature, pressure,density, and velocity. The boundary between theundisturbed air and the region of compressed air iscalled a shock or “compression” wave.

This same type of wave is formed whenever a super-sonic airstream is slowed to subsonic without a change

in direction, such as when the airstream is acceleratedto sonic speed over the cambered portion of a wing, andthen decelerates to subsonic speed as the area of maxi-mum camber is passed. A shock wave will form as aboundary between the supersonic and subsonic ranges.

Whenever a shock wave forms perpendicular to theairflow, it is termed a “normal” shock wave, and theflow immediately behind the wave is subsonic. Asupersonic airstream passing through a normal shockwave will experience these changes:

• The airstream is slowed to subsonic.

• The airflow immediately behind the shock wavedoes not change direction.

• The static pressure and density of the airstreambehind the wave is greatly increased.

• The energy of the airstream (indicated by totalpressure—dynamic plus static) is greatlyreduced.

Shock wave formation causes an increase in drag. Oneof the principal effects of a shock wave is the formationof a dense high pressure region immediately behind thewave. The instability of the high pressure region, andthe fact that part of the velocity energy of the airstreamis converted to heat as it flows through the wave is acontributing factor in the drag increase, but the dragresulting from airflow separation is much greater. If theshock wave is strong, the boundary layer may not havesufficient kinetic energy to withstand airflow separa-tion. The drag incurred in the transonic region due toshock wave formation and airflow separation is knownas “wave drag.” When speed exceeds the critical Machnumber by about 10 percent, wave drag increasessharply. A considerable increase in thrust (power) isrequired to increase flight speed beyond this point intothe supersonic range where, depending on the airfoilshape and the angle of attack, the boundary layer mayreattach.

Normal shock waves form on the wing’s uppersurface first. Further increases in Mach number,however, can enlarge the supersonic area on the

LaminarSub-Layer

TurbulentBoundary

LayerTransitionRegion

LaminarBoundary

Layer

Figure 3-42. Boundary layer.

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upper surface and form an additional area ofsupersonic flow and a normal shock wave on thelower surface. As flight speed approaches thespeed of sound, the areas of supersonic flowenlarge and the shock waves move nearer thetrailing edge. [Figure 3-43]

Figure 3-43. Shock waves.

Associated with “drag rise”are buffet (known as Machbuffet), trim and stabilitychanges, and a decrease incontrol force effectiveness.The loss of lift due to airflowseparation results in a loss ofdownwash, and a change inthe position of the centerpressure on the wing.Airflow separation producesa turbulent wake behind thewing which causes the tailsurfaces to buffet (vibrate).The nose-up and nose-downpitch control provided by thehorizontal tail is dependenton the downwash behind thewing. Thus, a decrease indownwash decreases thehorizontal tail’s pitch controleffectiveness. Movement ofthe wing center of pressureaffects the wing pitchingmoment. If the center ofpressure moves aft, a divingmoment referred to as“Mach tuck” or “tuck under”is produced, and if it movesforward, a nose-up momentis produced. This is the primaryreason for the development of

the T-tail configuration on many turbine-poweredairplanes, which places the horizontal stabilizer asfar as practical from the turbulence of the wings.

SWEEPBACKMost of the difficulties of transonic flight are asso-ciated with shock wave induced flow separation.Therefore, any means of delaying or alleviating theshock induced separation will improve aerodynamicperformance. One method is wing sweepback.Sweepback theory is based upon the concept that itis only the component of the airflow perpendicularto the leading edge of the wing that affects pressuredistribution and formation of shock waves. [Figure3-44]

On a straight wing airplane, the airflow strikes thewing leading edge at 90°, and its full impact producespressure and lift. A wing with sweepback is struck bythe same airflow at an angle smaller than 90°. Thisairflow on the swept wing has the effect of persuadingthe wing into believing that it is flying slower than itreally is; thus the formation of shock waves isdelayed. Advantages of wing sweep include anincrease in critical Mach number, force divergence

SupersonicFlow

M=.82

Normal Shock

Normal Shock

Separation

SupersonicFlow

M=.95

Normal Shock

Normal Shock

M=1.05

"Bow Wave"Subsonic

Airflow

Spanwise Flow

True AirspeedMach 0.85

AirspeedSensed By Wing

Mach 0.70

Figure 3-44. Sweepback effect.

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Mach number, and the Mach number at which drag risewill peak. In other words, sweep will delay the onset ofcompressibility effects.

The Mach number, which produces a sharp change indrag coefficient, is termed the “force divergence”Mach number and, for most airfoils, usually exceedsthe critical Mach number by 5 to 10 percent. At thisspeed, the airflow separation induced by shock waveformation can create significant variations in the drag,lift, or pitching moment coefficients. In addition tothe delay of the onset of compressibility effects,sweepback reduces the magnitude in the changes ofdrag, lift or moment coefficients. In other words, theuse of sweepback will “soften” the force divergence.

A disadvantage of swept wings is that they tend tostall at the wingtips rather than at the wing roots.[Figure 3-45] This is because the boundary layer tendsto flow spanwise toward the tips and to separate nearthe leading edges. Because the tips of a swept wingare on the aft part of the wing (behind the center oflift), a wingtip stall will cause the center of lift tomove forward on the wing, forcingthe nose to rise further. The tendencyfor tip stall is greatest when wingsweep and taper are combined.

Figure 3-45 Wingtip stall.

The stall situation can be aggravated by a T-tail config-uration, which affords little or no pre-stall warning inthe form of tail control surface buffet. [Figure 3-46]The T-tail, being above the wing wake remainseffective even after the wing has begun to stall,allowing the pilot to inadvertently drive the winginto a deeper stall at a much greater angle of attack.If the horizontal tail surfaces then become buried in the

wing’s wake, the elevator may lose all effectiveness,making it impossible to reduce pitch attitude and breakthe stall. In the pre-stall and immediate post-stallregimes, the lift/drag qualities of a swept wing airplane(specifically the enormous increase in drag at lowspeeds) can cause an increasingly descending flight-path with no change in pitch attitude, further increasingthe angle of attack. In this situation, without reliableangle of attack information, a nose-down pitch attitudewith an increasing airspeed is no guarantee that recoveryhas been effected, and up-elevator movement at thisstage may merely keep the airplane stalled.

It is a characteristic of T-tail airplanes to pitchup viciously when stalled in extreme nose-highattitudes, making recovery difficult or violent. Thestick pusher inhibits this type of stall. At approxi-mately one knot above stall speed, pre-programmedstick forces automatically move the stick forward,preventing the stall from developing. A “g” limitermay also be incorporated into the system to preventthe pitch down generated by the stick pusher fromimposing excessive loads on the airplane. A “stick

shaker,” on the other hand provides stall warningwhen the airspeed is 5 to 7 percent above stall speed.

MACH BUFFET BOUNDARIESThus far, only the Mach buffet that results fromexcessive speed has been addressed. It must beremembered that Mach buffet is a function of thespeed of the airflow over the wing—not necessarilythe speed of the airplane. Any time that too great a

IntitialStall Area

Pre-Stall

Stalled

Figure 3-46.T-tail stall.

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lift demand is made on the wing, whether from toofast an airspeed or from too high an angle of attacknear the MMO, the “high-speed” buffet will occur.However, there are also occasions when the buffetcan be experienced at much lower speeds known asthe “low-speed Mach buffet.”

The most likely situation that could cause the low-speed buffet would be when the airplane is flownat too slow a speed for its weight and altitudenecessitating a high angle of attack. This very highangle of attack would have the effect of increasingairflow velocity over the upper surface of the wingto the point that all of the same effects of the shockwaves and buffet would occur as in the high-speedbuffet situation. The angle of attack of the winghas the greatest effect on inducing the Mach buffetat either the high-speed or low-speed boundariesfor the airplane. The conditions that increase theangle of attack, hence the speed of the airflow overthe wing and chances of Mach buffet are as follows:

• High Altitudes—The higher an airplane flies, thethinner the air and the greater the angle of attackrequired to produce the lift needed to maintainlevel flight.

• Heavy Weights—The heavier the airplane, thegreater the lift required of the wing, and all otherthings being equal, the greater the angle of attack.

• “G” Loading—An increase in the “G” loadingon the airplane has the same effect as increasingthe weight of the airplane. Whether the increasein “G” forces is caused by turns, rough controlusage, or turbulence, the effect of increasing thewing’s angle of attack is the same.

FLIGHT CONTROLSOn high-speed airplanes, flight controls are dividedinto primary flight controls and secondary or auxil-iary flight controls. The primary flight controlsmaneuver the airplane about the pitch, roll, and yawaxes. They include the ailerons, elevator, and rudder.Secondary or auxiliary flight controls include tabs,leading edge flaps, trailing edge flaps, spoilers, andslats.

Spoilers are used on the upper surface of the wing tospoil or reduce lift. High-speed airplanes, due totheir clean low drag design use spoilers as speedbrakes to slow them down. Spoilers are extendedimmediately after touchdown to dump lift and thustransfer the weight of the airplane from the wingsonto the wheels for better braking performance.[Figure 3-47]

Jet transport airplanes have small ailerons. The spacefor ailerons is limited because as much of the wing

trailing edge as possible is needed for flaps. Anotherreason is that a conventional size aileron would causewing twist at high speed. Because the ailerons are nec-essarily small, spoilers are used in unison with aileronsto provide additional roll control.

Some jet transports have two sets of ailerons; a pair ofoutboard low-speed ailerons, and a pair of high-speedinboard ailerons. When the flaps are fully retractedafter takeoff, the outboard ailerons are automaticallylocked out in the faired position.

When used for roll control, the spoiler on the side ofthe up-going aileron extends and reduces the lift on thatside, causing the wing to drop. If the spoilers areextended as speed brakes, they can still be used for rollcontrol. If they are the Differential type, they willextend further on one side and retract on the other side.If they are the Non-Differential type, they will extendfurther on one side but will not retract on the other side.When fully extended as speed brakes, the Non-Differential spoilers remain extended and do not sup-plement the ailerons.

To obtain a smooth stall and a higher angle of attackwithout airflow separation, an airplane’s wing leadingedge should have a well-rounded almost blunt shapethat the airflow can adhere to at the higher angle ofattack. With this shape, the airflow separation will startat the trailing edge and progress forward gradually asangle of attack is increased.

The pointed leading edge necessary for high-speedflight results in an abrupt stall and restricts the useof trailing edge flaps because the airflow cannotfollow the sharp curve around the wing leadingedge. The airflow tends to tear loose rather suddenlyfrom the upper surface at a moderate angle of attack.To utilize trailing edge flaps, and thus increase themaximum lift coefficient, the wing must go to ahigher angle of attack without airflow separation.Therefore, leading edge slots, slats, and flaps areused to improve the low-speed characteristics duringtakeoff, climb, and landing. Although these devicesare not as powerful as trailing edge flaps, they areeffective when used full span in combination withhigh-lift trailing edge flaps. With the aid of thesesophisticated high-lift devices, airflow separation isdelayed and the maximum lift coefficient (CLmax) isincreased considerably. In fact, a 50-knot reductionin stall speed is not uncommon.

The operational requirements of a large jet transportairplane necessitate large pitch trim changes. Someof these requirements are:

• The requirement for a large CG range.

• The need to cover a large speed range.

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• The need to cope with possibly large trimchanges due to wing leading edge and trailingedge high-lift devices without limiting theamount of elevator remaining.

• The need to reduce trim drag to a minimum.

These requirements are met by the use of a variableincidence horizontal stabilizer. Large trim changeson a fixed-tail airplane require large elevator deflec-tions. At these large deflections, little further elevatormovement remains in the same direction. A variableincidence horizontal stabilizer is designed to take outthe trim changes. The stabilizer is larger than theelevator, and consequently does not need to bemoved through as large an angle. This leaves theelevator streamlining the tail plane with a full rangeof movement up and down. The variable incidencehorizontal stabilizer can be set to handle the bulk ofthe pitch control demand, with the elevator handlingthe rest. On airplanes equipped with a variable

incidence horizontal stabilizer, the elevator issmaller and less effective in isolation than it is ona fixed-tail airplane. In comparison to other flightcontrols, the variable incidence horizontal stabi-lizer is enormously powerful in its effect. Its useand effect must be fully understood and appreci-ated by flight crewmembers.

Because of the size and high speeds of jet transportairplanes, the forces required to move the controlsurfaces can be beyond the strength of the pilot.Consequently, the control surfaces are actuated byhydraulic or electrical power units. Moving the con-trols in the cockpit signals the control anglerequired, and the power unit positions the actualcontrol surface. In the event of complete power unitfailure, movement of the control surface can beeffected by manually controlling the control tabs.Moving the control tab upsets the aerodynamicbalance which causes the control surface to move.

Landing Flaps

Inbd Wing

Outbd Wing

ForeflapMidflap

Aftflap

Aileron

Takeoff FlapsInbd Wing

Outbd Wing

Aileron

Flaps RetractedInbd Wing

Outbd Wing

ForeflapMidflap

AftflapLeading EdgeFlap

Leading EdgeSlat

Aileron

737

LeadingEdge Flaps

Leading Edge Slats Tab Aileron

OutbdFlap

FlightSpoilers

Stabilizer

TabElevator

Rudder

Inbd Flap

Ground Spoiler

727

Control Surfaces

Fence

Balance Tab

Outboard Aileron

Slats

Inboard Aileron

Leading EdgeFlaps

Ground SpoilersInboard Flaps

Flight Spoilers

Lower Rudder

Anti-BalanceTabs

Upper Rudder

ControlTab

ElevatorStabilizer

Vortex Generators

Pitot TubesOutboard Flap

Control Tab

Figure 3-47. Control surfaces.

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4-1

Aircraft flight control systems are classified as primaryand secondary. The primary control systems consist ofthose that are required to safely control an airplane during flight. These include the ailerons, elevator (orstabilator), and rudder. Secondary control systemsimprove the performance characteristics of the airplane, or relieve the pilot of excessive control forces.Examples of secondary control systems are wing flapsand trim systems.

PRIMARY FLIGHT CONTROLSAirplane control systems are carefully designed to provide a natural feel, and at the same time, allow adequate responsiveness to control inputs. At low airspeeds, the controls usually feel soft and sluggish,and the airplane responds slowly to control applications.At high speeds, the controls feel firm and the responseis more rapid.

Movement of any of the three primary flight controlsurfaces changes the airflow and pressure distributionover and around the airfoil. These changes affect thelift and drag produced by the airfoil/control surfacecombination, and allow a pilot to control the airplaneabout its three axes of rotation.

Design features limit the amount of deflection of flight control surfaces. For example, control-stop mechanisms may be incorporated into the flight controls, or movement of the control column and/orrudder pedals may be limited. The purpose of thesedesign limits is to prevent the pilot from inadvertently overcontrolling and overstressing the aircraft duringnormal maneuvers.

A properly designed airplane should be stable and easily controlled during maneuvering. Control surfaceinputs cause movement about the three axes of rota-tion. The types of stability an airplane exhibits alsorelate to the three axes of rotation. [Figure 4-1]

AILERONSAilerons control roll about the longitudinal axis. Theailerons are attached to the outboard trailing edge of

Vertical Axis(Directional Stability)

Rudder-YawMovement

Elevator-PitchMovement

Lateral Axis(Longitudinal Stability)

Longitudinal Axis(Lateral Stability)

Aileron-RollMovement

PRIMARYCONTROLSURFACE

AIRPLANEMOVEMENT

AXES OFROTATION

TYPE OFSTABILITY

Aileron Roll Longitudinal Lateral

Rudder Yaw Vertical Directional

Elevator/Stabilator Pitch Lateral Longitudinal

Figure 4-1. Airplane controls, movement, axes of rotation, andtype of stability.

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each wing and move in the opposite direction from each other. Ailerons are connected by cables, bellcranks, pulleys or push-pull tubes to each other and to the control wheel.

Moving the control wheel to the right causes the rightaileron to deflect upward and the left aileron to deflectdownward. The upward deflection of the right ailerondecreases the camber resulting in decreased lift on theright wing. The corresponding downward deflection ofthe left aileron increases the camber resulting inincreased lift on the left wing. Thus, the increased lifton the left wing and the decreased lift on the right wingcauses the airplane to roll to the right.

ADVERSE YAWSince the downward deflected aileron produces morelift, it also produces more drag. This added dragattempts to yaw the airplane’s nose in the direction ofthe raised wing. This is called adverse yaw. [Figure 4-2]

The rudder is used to counteract adverse yaw, and theamount of rudder control required is greatest at low airspeeds, high angles of attack, and with large ailerondeflections. However, with lower airspeeds, the verticalstabilizer/rudder combination becomes less effective,and magnifies the control problems associated withadverse yaw.

All turns are coordinated by use of ailerons, rudder, andelevator. Applying aileron pressure is necessary toplace the airplane in the desired angle of bank, whilesimultaneously applying rudder pressure to counteractthe resultant adverse yaw. During a turn, the angle ofattack must be increased by applying elevator pressurebecause more lift is required than when in straight-and-level flight. The steeper the turn, the more back elevator pressure is needed.

As the desired angle of bank is established, aileron andrudder pressures should be relaxed. This will stop thebank from increasing because the aileron and ruddercontrol surfaces will be neutral in their streamlinedposition. Elevator pressure should be held constant tomaintain a constant altitude.

The rollout from a turn is similar to the roll-in exceptthe flight controls are applied in the opposite direction.Aileron and rudder are applied in the direction of therollout or toward the high wing. As the angle of bankdecreases, the elevator pressure should be relaxed asnecessary to maintain altitude.

DIFFERENTIAL AILERONSWith differential ailerons, one aileron is raised a greaterdistance than the other aileron is lowered for a givenmovement of the control wheel. This produces anincrease in drag on the descending wing. The greater drag results from deflecting the up aileron on the descending wing to a greater angle than the downaileron on the rising wing. While adverse yaw isreduced, it is not eliminated completely. [Figure 4-3]

FRISE-TYPE AILERONSWith a Frise-type aileron, when pressure is applied tothe control wheel, the aileron that is being raised pivotson an offset hinge. This projects the leading edge of theaileron into the airflow and creates drag. This helpsequalize the drag created by the lowered aileron on theopposite wing and reduces adverse yaw. [Figure 4-4]

AdverseYaw

Figure 4-2. Adverse yaw is caused by higher drag on the outside wing, which is producing more lift.

Neutral

Raised

Lowered

Figure 4-4. Frise-type ailerons.

Figure 4-3. Differential ailerons.

Up AileronDeflection

Down AileronDeflection

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The Frise-type aileron also forms a slot so that air flowssmoothly over the lowered aileron, making it moreeffective at high angles of attack. Frise-type aileronsalso may be designed to function differentially. Likethe differential aileron, the Frise-type aileron does noteliminate adverse yaw entirely. Coordinated rudderapplication is still needed wherever ailerons areapplied.

COUPLED AILERONS AND RUDDERCoupled ailerons and rudder means these controls arelinked. This is accomplished with rudder-aileron interconnect springs, which help correct for ailerondrag by automatically deflecting the rudder at the sametime the ailerons are deflected. For example, when thecontrol yoke is moved to produce a left roll, the interconnect cable and spring pulls forward on the leftrudder pedal just enough to prevent the nose of the airplane from yawing to the right. The force applied tothe rudder by the springs can be overridden if itbecomes necessary to slip the airplane. [Figure 4-5]

ELEVATORThe elevator controls pitch about the lateral axis. Likethe ailerons on small airplanes, the elevator is connected to the control column in the cockpit by aseries of mechanical linkages. Aft movement of thecontrol column deflects the trailing edge of the elevatorsurface up. This is usually referred to as up elevator.[Figure 4-6]

The up-elevator position decreases the camber of theelevator and creates a downward aerodynamic force,which is greater than the normal tail-down force thatexists in straight-and-level flight. The overall effectcauses the tail of the airplane to move down and thenose to pitch up. The pitching moment occurs about thecenter of gravity (CG). The strength of the pitchingmoment is determined by the distance between the CGand the horizontal tail surface, as well as by the aerodynamic effectiveness of the horizontal tail surface.

Moving the control column forward has the oppositeeffect. In this case, elevator camber increases, creatingmore lift (less tail-down force) on the horizontal stabilizer/elevator. This moves the tail upward andpitches the nose down. Again, the pitching momentoccurs about the CG.

As mentioned earlier in the coverage on stability,power, thrustline, and the position of the horizontal tailsurfaces on the empennage are factors in how effectivethe elevator is in controlling pitch. For example, thehorizontal tail surfaces may be attached near the lowerpart of the vertical stabilizer, at the midpoint, or at thehigh point, as in the T-tail design.

T-TAILIn a T-tail configuration, the elevator is above most ofthe effects of downwash from the propeller as well asairflow around the fuselage and/or wings during normal flight conditions. Operation of the elevators inthis undisturbed air makes for control movements thatare consistent throughout most flight regimes. T-taildesigns have become popular on many light airplanesand on large aircraft, especially those with aft-fuselagemounted engines since the T-tail configuration removesthe tail from the exhaust blast of the engines. Seaplanesand amphibians often have T-tails in order to keep thehorizontal surfaces as far from the water as possible.An additional benefit is reduced vibration and noiseinside the aircraft.

At slow speeds, the elevator on a T-tail aircraft must bemoved through a larger number of degrees of travel to raise the nose a given amount as compared to a conventional-tail aircraft. This is because the

Control ColumnAft Up

Elevator

DownwardAerodynamic Force

CGNose

UpTail

Down

Figure 4-6. The elevator is the primary control for changingthe pitch attitude of an airplane.

Rudder Deflects with Ailerons

Rudder/AileronInterconnectingSprings

Figure 4-5. Coupled ailerons and rudder.

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conventional-tail aircraft has the downwash from thepropeller pushing down on the tail to assist in raisingthe nose. Since controls on aircraft are rigged in such amanner as to require increasing control forces forincreased control travel, the forces required to raise thenose of a T-tail aircraft are greater than for a conventional-tail aircraft. Longitudinal stability of atrimmed aircraft is the same for both types of configuration, but the pilot must be aware that at slowspeeds during takeoffs and landings or stalls, the control forces will be greater than for similar size airplanes equipped with conventional tails.

T-tail airplanes also require additional designconsiderations to counter the problem of flutter. Sincethe weight of the horizontal surfaces is at the top of thevertical stabilizer, the moment arm created causes highloads on the vertical stabilizer which can result influtter. Engineers must compensate for this by increasing the design stiffness of the vertical stabilizer,usually resulting in a weight penalty over conventionaltail designs.

When flying at a very high angle of attack with a lowairspeed and an aft CG, the T-tail airplane may be susceptible to a deep stall. In a deep stall, the airflowover the horizontal tail is blanketed by the disturbedairflow from the wings and fuselage. In these circumstances, elevator or stabilator control could bediminished, making it difficult to recover from the stall. It should be noted that an aft CG could be a contributing factor in these incidents since similar recovery problems are also found with conventional-tail aircraft with an aft CG. [Figure 4-7]

Since flight at a high angle of attack with a low airspeed and an aft CG position can be dangerous,many airplanes have systems to compensate for this situation. The systems range from control stops to elevator down springs. An elevator down spring assistsin lowering the nose to prevent a stall caused by the aftCG position. The stall occurs because the properlytrimmed airplane is flying with the elevator in a trailingedge down position, forcing the tail up and the nosedown. In this unstable condition, if the airplaneencounters turbulence and slows down further, the trim

tab no longer positions the elevator in the nose-downposition. The elevator then streamlines, and the nose ofthe aircraft pitches upward. This aggravates the situation and can possibly result in a stall.

The elevator down spring produces a mechanical loadon the elevator, causing it to move toward the nose-down position if not otherwise balanced. The elevatortrim tab balances the elevator down spring to positionthe elevator in a trimmed position. When the trim tabbecomes ineffective, the down spring drives the elevator to a nose down position. The nose of the aircraft lowers, speed builds up, and a stall is prevented. [Figure 4-8]

The elevator must also have sufficient authority to holdthe nose of the airplane up during the roundout for alanding. In this case, a forward CG may cause a problem. During the landing flare, power normally isreduced, which decreases the airflow over the empennage. This, coupled with the reduced landingspeed, makes the elevator less effective.

From this discussion, it should be apparent that pilotsmust understand and follow proper loading procedures,particularly with regard to the CG position. More information on aircraft loading, as well as weight andbalance, is included in Chapter 8.

STABILATORAs mentioned in Chapter 1, a stabilator is essentially aone-piece horizontal stabilizer with the same type ofcontrol system. Because stabilators pivot around a central hinge point, they are extremely sensitive to control inputs and aerodynamic loads.

Antiservo tabs are incorporated on the trailing edge todecrease sensitivity. In addition, a balance weight isusually incorporated ahead of the main spar. Thebalance weight may project into the empennage or maybe incorporated on the forward portion of thestabilator tips. [Figure 4-9]

Down Spring Elevator

Stabilizer

Figure 4-8.When the aerodynamic efficiency of the horizontaltail surface is inadequate due to an aft center of gravity con-dition, an elevator down spring may be used to supply amechanical load to lower the nose.

Figure 4-7. Airplane with a T-tail design at a high angle ofattack and an aft CG.

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When the control column is pulled back, it raises thestabilator’s trailing edge, rotating the airplane’s noseup. Pushing the control column forward lowers thetrailing edge of the stabilator and pitches the nose ofthe airplane down. Without an antiservo tab, the airplane would be prone to overcontrolling frompilot-induced control inputs.

CANARDThe term canard refers to a control surface that functions as a horizontal stabilizer but is located infront of the main wings. The term also is used todescribe an airplane equipped with a canard. In effect,it is an airfoil similar to the horizontal surface on a conventional aft-tail design. The difference is that thecanard actually creates lift and holds the nose up, asopposed to the aft-tail design which exerts downwardforce on the tail to prevent the nose from rotating downward. [Figure 4-10]

Although the Wright Flyer was configured as a canard with the horizontal surfaces in front of the lifting surface, it was not until recently that thecanard configuration began appearing on newer airplanes. Canard designs include two types—one witha horizontal surface of about the same size as a normalaft-tail design, and the other with a surface of the sameapproximate size and airfoil of the aft-mounted wingknown as a tandem wing configuration. Theoretically,the canard is considered more efficient because usingthe horizontal surface to help lift the weight of the aircraft should result in less drag for a given amount of lift.

The canard’s main advantage is in the area of stall characteristics. A properly designed canard or tandemwing will run out of authority to raise the nose of theaircraft at a point before the main wing will stall. Thismakes the aircraft stall-proof and results only in adescent rate that can be halted by adding power.Ailerons on the main wing remain effective throughoutthe recovery. Other canard configurations are designedso the canard stalls before the main wing, automaticallylowering the nose and recovering the aircraft to a safeflying speed. Again, the ailerons remain effectivethroughout the stall.

The canard design has several limitations. First, it isimportant that the forward lifting surface of a canarddesign stalls before the main wing. If the main wingstalls first, the lift remaining from the forward wing orcanard would be well ahead of the CG, and the airplanewould pitch up uncontrollably. Second, when the for-ward surface stalls first, or is limited in its ability toincrease the angle of attack, the main wing neverreaches a point where its maximum lift is created, sacrificing some performance. Third, use of flaps onthe main wing causes design problems for the forwardwing or canard. As lift on the main wing is increasedby extension of flaps, the lift requirement of the canardis also increased. The forward wing or canard must belarge enough to accommodate flap use, but not so largethat it creates more lift than the main wing.

Finally, the relationship of the main wing to the forward surface also makes a difference. When positioned closely in the vertical plane, downwashfrom the forward wing can have a negative effect onthe lift of the main wing. Increasing vertical separationincreases efficiency of the design. Efficiency is alsoincreased as the size of the two surfaces grows closer tobeing equal.

RUDDERThe rudder controls movement of the airplane about itsvertical axis. This motion is called yaw. Like the

Pivot Point

Antiservo TabStabilator

BalanceWeight

Figure 4-9. The stabilator is a one-piece horizontal tail sur-face that pivots up and down about a central hinge point.

Canard—A horizontal surface mounted ahead of the main wing to pro-vide longitudinal stability and control. It may be a fixed, movable, orvariable geometry surface, with or without control surfaces.

Canard Configuration—A configuration in which the span of the for-ward wings is substantially less than that of the main wing.

Figure 4-10.This advanced aircraft includes a variable-sweepcanard design, which provides longitudinal stability aboutthe lateral axis.

Courtesy of Raytheon Corporation

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other primary control surfaces, the rudder is a movable surface hinged to a fixed surface, in this case, to the vertical stabilizer, or fin. Moving the left or right rudder pedal controls the rudder. When the rudder is deflected into the airflow, a horizontal force is exerted in the opposite direction.[Figure 4-11]

By pushing the left pedal, the rudder moves left. Thisalters the airflow around the vertical stabilizer/rudder,and creates a sideward lift that moves the tail to theright and yaws the nose of the airplane to the left.Rudder effectiveness increases with speed, so largedeflections at low speeds and small deflections at highspeeds may be required to provide the desired reaction.In propeller-driven aircraft, any slipstream flowingover the rudder increases its effectiveness.

V-TAILThe V-tail design utilizes two slanted tail surfaces toperform the same functions as the surfaces of a con-ventional elevator and rudder configuration. The fixedsurfaces act as both horizontal and vertical stabilizers.[Figure 4-12]

The movable surfaces, which are usually called ruddervators, are connected through a special linkagethat allows the control wheel to move both surfacessimultaneously. On the other hand, displacement of therudder pedals moves the surfaces differentially, therebyproviding directional control.

When both rudder and elevator controls are moved bythe pilot, a control mixing mechanism moves each surface the appropriate amount. The control system forthe V-tail is more complex than that required for a conventional tail. In addition, the V-tail design is moresusceptible to Dutch roll tendencies than a conven-tional tail and total reduction in drag is only minimal.

SECONDARY FLIGHT CONTROLSSecondary flight control systems may consist of theflaps, leading edge devices, spoilers, and trim devices.

FLAPSFlaps are the most common high-lift devices used onpractically all airplanes. These surfaces, which areattached to the trailing edge of the wing, increase bothlift and induced drag for any given angle of attack.Flaps allow a compromise between high cruising speedand low landing speed, because they may be extendedwhen needed, and retracted into the wing’s structurewhen not needed. There are four common typesof flaps: plain, split, slotted, and Fowler flaps.[Figure 4-13]

The plain flap is the simplest of the four types. Itincreases the airfoil camber, resulting in a significantincrease in the coefficient of lift at a given angle ofattack. At the same time, it greatly increases drag andmoves the center of pressure aft on the airfoil, resultingin a nose-down pitching moment.

Ruddervator—A pair of control surfaces on the tail of an aircraftarranged in the form of a V. These surfaces, when moved together bythe control wheel, serve as elevators, and when moved differentially bythe rudder pedals, serve as a rudder.

Yaw

Left RudderForward

AerodynamicForce

LeftRudder

CG

Figure 4-11.The effect of left rudder pressure.

Figure 4-12. V-tail design.

Plain Flap

Slotted Flap

Split Flap

Fowler Flap

Figure 4-13. Four common types of flaps

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The split flap is deflected from the lower surface of theairfoil and produces a slightly greater increase in liftthan does the plain flap. However, more drag is createdbecause of the turbulent air pattern produced behindthe airfoil. When fully extended, both plain and splitflaps produce high drag with little additional lift.

The most popular flap on airplanes today is the slottedflap. Variations of this design are used for small airplanes as well as for large ones. Slotted flapsincrease the lift coefficient significantly more thanplain or spilt flaps. On small airplanes, the hinge islocated below the lower surface of the flap, and whenthe flap is lowered, it forms a duct between the flapwell in the wing and the leading edge of the flap.

When the slotted flap is lowered, high-energy air fromthe lower surface is ducted to the flap’s upper surface.The high-energy air from the slot accelerates the uppersurface boundary layer and delays airflow separation,providing a higher coefficient of lift. Thus, the slottedflap produces much greater increases in CLmax than theplain or split flap. While there are many types of slotted flaps, large airplanes often have double- and eventriple-slotted flaps. These allow the maximum increase indrag without the airflow over the flaps separating anddestroying the lift they produce.

Fowler flaps are a type of slotted flap. This flap designnot only changes the camber of the wing, it alsoincreases the wing area. Instead of rotating down on ahinge, it slides backwards on tracks. In the first portionof its extension, it increases the drag very little, butincreases the lift a great deal as it increases both thearea and camber. As the extension continues, the flapdeflects downward, and during the last portion of itstravel, it increases the drag with little additionalincrease in lift.

LEADING EDGE DEVICESHigh-lift devices also can be applied to the leading edgeof the airfoil. The most common types are fixed slots,movable slats, and leading edge flaps. [Figure 4-14]

Fixed slots direct airflow to the upper wing surface anddelay airflow separation at higher angles of attack. Theslot does not increase the wing camber, but allows ahigher maximum coefficient of lift because the stall isdelayed until the wing reaches a greater angle of attack.

Movable slats consist of leading edge segments, whichmove on tracks. At low angles of attack, each slat is held flush against the wing’s leading edge by the highpressure that forms at the wing’s leading edge. As theangle of attack increases, the high-pressure area movesaft below the lower surface of the wing, allowing the slats to move forward. Some slats, however, arepilot operated and can be deployed at any angle ofattack. Opening a slat allows the air below the wingto flow over the wing’s upper surface, delaying airflow separation.

Leading edge flaps, like trailing edge flaps, are used toincrease both CLmax and the camber of the wings. Thistype of leading edge device is frequently used in conjunction with trailing edge flaps and can reduce thenose-down pitching movement produced by the latter.As is true with trailing edge flaps, a small increment ofleading edge flaps increases lift to a much greaterextent than drag. As greater amounts of flaps areextended, drag increases at a greater rate than lift.

SPOILERSOn some airplanes, high-drag devices called spoilersare deployed from the wings to spoil the smooth airflow, reducing lift and increasing drag. Spoilers areused for roll control on some aircraft, one of theadvantages being the elimination of adverse yaw. Toturn right, for example, the spoiler on the right wing israised, destroying some of the lift and creating moredrag on the right. The right wing drops, and the airplanebanks and yaws to the right. Deploying spoilers on bothwings at the same time allows the aircraft to descendwithout gaining speed. Spoilers are also deployed tohelp shorten ground roll after landing. By destroyinglift, they transfer weight to the wheels, improving braking effectiveness. [Figure 4-15]

Fixed Slot

Movable Slat

Leading Edge Flap

Figure 4-14. Leading edge high lift devices.Figure 4-15. Spoilers reduce lift and increase drag duringdescent and landing.

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4-8

TRIM SYSTEMSAlthough the airplane can be operated throughout a wide range of attitudes, airspeeds, and power settings, it can only be designed to fly hands off within a very limited combination of these variables.Therefore, trim systems are used to relieve the pilot of the need to maintain constant pressure on the flightcontrols. Trim systems usually consist of cockpit controls and small hinged devices attached to the trailing edge of one or more of the primary flight control surfaces. They are designed to help minimize a pilot’s workload by aerodynamically assisting movement and position of the flight control surface towhich they are attached. Common types of trim systems include trim tabs, balance tabs, antiservo tabs, ground adjustable tabs, and an adjustable stabilizer.

TRIM TABSThe most common installation on small airplanes is asingle trim tab attached to the trailing edge of the elevator. Most trim tabs are manually operated by asmall, vertically mounted control wheel. However, a trim crank may be found in some airplanes. The cockpit control includes a tab position indicator.Placing the trim control in the full nose-down position moves the tab to its full up position. With thetab up and into the airstream, the airflow over the horizontal tail surface tends to force the trailing edge ofthe elevator down. This causes the tail of the airplaneto move up, and results in a nose-down pitch change.[Figure 4-16]

If you set the trim tab to the full nose-up position, thetab moves to its full-down position. In this case, the airflowing under the horizontal tail surface hits the taband tends to force the trailing edge of the elevator up,reducing the elevator’s angle of attack. This causes atail-down movement of the airplane and a nose-uppitch change.

In spite of the opposite direction movement of the trimtab and the elevator, control of trim is natural to a pilot.If you have to exert constant back pressure on the control column, the need for nose-up trim is indicated.The normal trim procedure is to continue trimminguntil the airplane is balanced and the nose-heavy condition is no longer apparent. Pilots normally establish the desired power, pitch attitude, andconfiguration first, and then trim the airplane to relievecontrol pressures that may exist for that flight condition. Any time power, pitch attitude, orconfiguration is changed, expect that retrimming willbe necessary to relieve the control pressures for thenew flight condition.

BALANCE TABSThe control forces may be excessively high in some airplanes, and in order to decrease them, the manufacturer may use balance tabs. They look like trimtabs and are hinged in approximately the same placesas trim tabs. The essential difference between the twois that the balancing tab is coupled to the control surface rod so that when the primary control surface ismoved in any direction, the tab automatically moves inthe opposite direction. In this manner, the airflow striking the tab counter-balances some of the air pressure against the primary control surface, andenables the pilot to more easily move and hold the control surface in position.

If the linkage between the tab and the fixed surface isadjustable from the cockpit, the tab acts as a combination trim and balance tab, which can beadjusted to any desired deflection. Any time the controlsurface is deflected, the tab moves in the oppositedirection and eases the load on the pilot.

ANTISERVO TABSIn addition to decreasing the sensitivity of the stabilator, an antiservo tab also functions as a trimdevice to relieve control pressure and maintain the stabilator in the desired position. The fixed end of the linkage is on the opposite side of the surface from the horn on the tab, and when the trailing edge ofthe stabilator moves up, the linkage forces the trailingedge of the tab up. When the stabilator moves down,the tab also moves down. This is different than trimtabs on elevators, which move opposite of the control surface. [Figure 4-17]

Nose-Down Trim

Nose-Up Trim

Tab Up; Elevator Down

Tab Down; Elevator Up

Figure 4-16. The movement of the elevator is opposite to thedirection of movement of the elevator trim tab.

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This tab works in the same manner as the balance tabexcept that, instead of moving in the opposite direc-tion, it moves in the same direction as the trailing edgeof the stabilator. For example, when the trailing edgeof the stabilator moves up, the linkage forces the trailing edge of the tab up. When the stabilator movesdown, the tab also moves down.

GROUND ADJUSTABLE TABSMany small airplanes have a non-moveable metal trimtab on the rudder. This tab is bent in one direction orthe other while on the ground to apply a trim force tothe rudder. The correct displacement is determined bytrial-and-error process. Usually, small adjustments arenecessary until you are satisfied that the airplane is nolonger skidding left or right during normal cruisingflight. [Figure 4-18]

ADJUSTABLE STABILIZERRather than using a movable tab on the trailing edge ofthe elevator, some airplanes have an adjustable stabilizer. With this arrangement, linkages pivot the horizontal stabilizer about its rear spar. This isaccomplished by use of a jackscrew mounted on theleading edge of the stabilator. [Figure 4-19]

On small airplanes, the jackscrew is cable-operatedwith a trim wheel or crank, and on larger airplanes, it is motor driven. The trimming effect and cockpitindications for an adjustable stabilizer are similar tothose of a trim tab.

Since the primary and secondary flight control systems vary extensively between aircraft, you need tobe familiar with the systems in your aircraft. A goodsource of information is the Airplane Flight Manual(AFM) or the Pilot’s Operating Handbook (POH).

Figure 4-18. A ground-adjustable tab is used on the rudder ofmany small airplanes to correct for a tendency to fly with thefuselage slightly misaligned with the relative wind.

PivotJackscrew

Nose DownNose Up

Trim Motoror Trim Cable

Figure 4-19. Some airplanes, including most jet transports,use an adjustable stabilizer to provide the required pitch trimforces.

Stabilator

AntiservoTab

Pivot Point

Figure 4-17. An antiservo tab attempts to streamline the con-trol surface and is used to make the stabilator less sensitiveby opposing the force exerted by the pilot.

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5-1

This chapter covers the main systems found on smallairplanes. These include the engine, propeller, andinduction systems, as well as the ignition, fuel,lubrication, cooling, electrical, landing gear, autopilot,and environmental control systems. A comprehensiveintroduction to gas turbine engines is included at theend of this chapter.

POWERPLANTThe airplane engine and propeller, often referred to as apowerplant, work in combination to produce thrust.The powerplant propels the airplane and drives thevarious systems that support the operation ofan airplane.

RECIPROCATING ENGINESMost small airplanes are designed with reciprocatingengines. The name is derived from the back-and-forth,or reciprocating, movement of the pistons. It is thismotion that produces the mechanical energy needed toaccomplish work. Two common means of classifyingreciprocating engines are:

1. by cylinder arrangement with respect to thecrankshaft—radial, in-line, v-type or opposed, or

2. by the method of cooling—liquid or air-cooled.

Radial engines were widely used during World War II,and many are still in service today. With these engines,a row or rows of cylinders are arranged in a circularpattern around the crankcase. The main advantage of aradial engine is the favorable power-to-weight ratio.

In-line engines have a comparatively small frontal area,but their power-to-weight ratios are relatively low. Inaddition, the rearmost cylinders of an air-cooled,in-line engine receive very little cooling air, so theseengines are normally limited to four or six cylinders.V-type engines provide more horsepower than in-lineengines and still retain a small frontal area. Furtherimprovements in engine design led to the developmentof the horizontally-opposed engine.

Opposed-type engines are the most popular reciprocat-ing engines used on small airplanes. These enginesalways have an even number of cylinders, since acylinder on one side of the crankcase “opposes” acylinder on the other side. The majority of theseengines are air cooled and usually are mounted in ahorizontal position when installed on fixed-wingairplanes. Opposed-type engines have high power-to-weight ratios because they have a comparatively small,lightweight crankcase. In addition, the compactcylinder arrangement reduces the engine’s frontal areaand allows a streamlined installation that minimizesaerodynamic drag.

Powerplant—A complete engine and propeller combinationwith accessories.

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The main parts of a reciprocating engine include thecylinders, crankcase, and accessory housing. Theintake/exhaust valves, spark plugs, and pistons arelocated in the cylinders. The crankshaft and connectingrods are located in the crankcase. [Figure 5-1] Themagnetos are normally located on the engine accessoryhousing.

The basic principle for reciprocating engines involvesthe conversion of chemical energy, in the form of fuel,into mechanical energy. This occurs within thecylinders of the engine through a process known as thefour-stroke operating cycle. These strokes are calledintake, compression, power, and exhaust. [Figure 5-2]

1. The intake stroke begins as the piston starts itsdownward travel. When this happens, the intakevalve opens and the fuel/air mixture is drawn intothe cylinder.

2. The compression stroke begins when the intakevalve closes and the piston starts moving back tothe top of the cylinder. This phase of the cycle isused to obtain a much greater power output fromthe fuel/air mixture once it is ignited.

3. The power stroke begins when the fuel/airmixture is ignited. This causes a tremendouspressure increase in the cylinder, and forces thepiston downward away from the cylinder head,creating the power that turns the crankshaft.

4. The exhaust stroke is used to purge the cylinderof burned gases. It begins when the exhaust valveopens and the piston starts to move toward thecylinder head once again.

Even when the engine is operated at a fairly low speed,the four-stroke cycle takes place several hundred timeseach minute. In a four-cylinder engine, each cylinderoperates on a different stroke. Continuous rotation of acrankshaft is maintained by the precise timing of thepower strokes in each cylinder. Continuous operationof the engine depends on the simultaneous function ofauxiliary systems, including the induction, ignition,fuel, oil, cooling, and exhaust systems.

PROPELLERThe propeller is a rotating airfoil, subject to induceddrag, stalls, and other aerodynamic principles thatapply to any airfoil. It provides the necessary thrust topull, or in some cases push, the airplane through the air.The engine power is used to rotate the propeller, which

Intake Valve Exhaust Valve

Cylinder

Piston

Crankshaft

Connecting Rod

Crankcase

Figure 5-1. Main components of a reciprocating engine.

Intake Compression

Power Exhaust

IntakeValve

ExhaustValve

SparkPlug

Piston

ConnectingRod

Crankshaft

1 2

3 4

Figure 5-2. The arrows in this illustration indicate thedirection of motion of the crankshaft and piston during thefour-stroke cycle.

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in turn generates thrust very similar to the manner inwhich a wing produces lift. The amount of thrustproduced depends on the shape of the airfoil, the angleof attack of the propeller blade, and the r.p.m. of theengine. The propeller itself is twisted so the blade anglechanges from hub to tip. The greatest angle ofincidence, or the highest pitch, is at the hub while thesmallest pitch is at the tip. [Figure 5-3]

The reason for the twist is to produce uniform lift fromthe hub to the tip. As the blade rotates, there is adifference in the actual speed of the various portions ofthe blade. The tip of the blade travels faster than thatpart near the hub, because the tip travels a greaterdistance than the hub in the same length of time.Changing the angle of incidence (pitch) from the hubto the tip to correspond with the speed producesuniform lift throughout the length of the blade. If thepropeller blade was designed with the same angle ofincidence throughout its entire length, it would beinefficient, because as airspeed increases in flight, theportion near the hub would have a negative angle ofattack while the blade tip would be stalled. [Figure 5-4]

Small airplanes are equipped with either one of twotypes of propellers. One is the fixed-pitch, and the otheris the controllable-pitch.

FIXED-PITCH PROPELLERThe pitch of this propeller is set by the manufacturer,and cannot be changed. With this type of propeller, thebest efficiency is achieved only at a given combinationof airspeed and r.p.m.

There are two types of fixed-pitch propellers—theclimb propeller and the cruise propeller. Whether theairplane has a climb or cruise propeller installeddepends upon its intended use:

• The climb propeller has a lower pitch, thereforeless drag. Less drag results in higher r.p.m. andmore horsepower capability, which increasesperformance during takeoffs and climbs, butdecreases performance during cruising flight.

• The cruise propeller has a higher pitch, thereforemore drag. More drag results in lower r.p.m. andless horsepower capability, which decreasesperformance during takeoffs and climbs, butincreases efficiency during cruising flight.

The propeller is usually mounted on a shaft, which maybe an extension of the engine crankshaft. In this case,the r.p.m. of the propeller would be the same as thecrankshaft r.p.m. On some engines, the propeller ismounted on a shaft geared to the engine crankshaft. Inthis type, the r.p.m. of the propeller is different thanthat of the engine. In a fixed-pitch propeller, thetachometer is the indicator of engine power.[Figure 5-5]

A tachometer is calibrated in hundreds of r.p.m., andgives a direct indication of the engine and propellerr.p.m. The instrument is color-coded, with a green arcdenoting the maximum continuous operating r.p.m.Some tachometers have additional markings to reflect

Angle of Incidence—For a propeller, it is the angle formed by the chordline and the reference plane containing the propeller hub. For a wing, itis the angle formed by the chord line of the wing and the longitudinalaxis of the airplane.

Figure 5-3. Changes in propeller blade angle from hub to tip.

Mod

erat

e

Travel Distance – Moderate Speed

Sho

rt

Travel Distance

Slow Speed

Gre

ater Travel Distance – Very High Speed

2500 r.p.m.

2500 r.p.m.

2500 r.p.m

Figure 5-4. Relationship of travel distance and speed ofvarious portions of propeller blade.

Figure 5-5. Engine r.p.m. is indicated on the tachometer.

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engine and/or propeller limitations. Therefore, themanufacturer’s recommendations should be used as areference to clarify any misunderstanding oftachometer markings.

The revolutions per minute are regulated by thethrottle, which controls the fuel/air flow to the engine.At a given altitude, the higher the tachometer reading,the higher the power output of the engine.

When operating altitude increases, the tachometer maynot show correct power output of the engine. Forexample, 2,300 r.p.m. at 5,000 feet produce lesshorsepower than 2,300 r.p.m. at sea level. The reasonfor this is that power output depends on air density. Airdensity decreases as altitude increases. Therefore, adecrease in air density (higher density altitude)decreases the power output of the engine. As altitudechanges, the position of the throttle must be changed tomaintain the same r.p.m. As altitude is increased, thethrottle must be opened further to indicate the samer.p.m. as at a lower altitude.

ADJUSTABLE-PITCH PROPELLERAlthough some older adjustable-pitch propellers couldonly be adjusted on the ground, most modernadjustable-pitch propellers are designed so that you canchange the propeller pitch in flight. The firstadjustable-pitch propeller systems provided only twopitch settingsa low-pitch setting and a high-pitchsetting. Today, however, nearly all adjustable-pitchpropeller systems are capable of a range ofpitch settings.

A constant-speed propeller is the most common type ofadjustable-pitch propeller. The main advantage of aconstant-speed propeller is that it converts a highpercentage of brake horsepower (BHP) into thrusthorsepower (THP) over a wide range of r.p.m. andairspeed combinations. A constant-speed propeller ismore efficient than other propellers because it allowsselection of the most efficient engine r.p.m. for thegiven conditions.

An airplane with a constant-speed propeller has twocontrols—the throttle and the propeller control. Thethrottle controls power output, and the propellercontrol regulates engine r.p.m. and, in turn, propellerr.p.m., which is registered on the tachometer.

Once a specific r.p.m. is selected, a governorautomatically adjusts the propeller blade angle asnecessary to maintain the selected r.p.m. For example,after setting the desired r.p.m. during cruising flight, anincrease in airspeed or decrease in propeller load willcause the propeller blade angle to increase as necessaryto maintain the selected r.p.m. A reduction in airspeedor increase in propeller load will cause the propellerblade angle to decrease.

The range of possible blade angles for a constant-speedpropeller is the propeller’s constant-speed range and isdefined by the high and low pitch stops. As long as thepropeller blade angle is within the constant-speed rangeand not against either pitch stop, a constant enginer.p.m. will be maintained. However, once the propellerblades contact a pitch stop, the engine r.p.m. willincrease or decrease as appropriate, with changes inairspeed and propeller load. For example, once aspecific r.p.m. has been selected, if aircraft speeddecreases enough to rotate the propeller blades untilthey contact the low pitch stop, any further decrease inairspeed will cause engine r.p.m. to decrease the sameway as if a fixed-pitch propeller were installed. Thesame holds true when an airplane equipped with aconstant-speed propeller accelerates to a fasterairspeed. As the aircraft accelerates, the propeller bladeangle increases to maintain the selected r.p.m. until thehigh pitch stop is reached. Once this occurs, the bladeangle cannot increase any further and enginer.p.m. increases.

On airplanes that are equipped with a constant-speedpropeller, power output is controlled by the throttle andindicated by a manifold pressure gauge. The gaugemeasures the absolute pressure of the fuel/air mixtureinside the intake manifold and is more correctly ameasure of manifold absolute pressure (MAP). At aconstant r.p.m. and altitude, the amount of powerproduced is directly related to the fuel/air flow beingdelivered to the combustion chamber. As you increasethe throttle setting, more fuel and air is flowing to theengine; therefore, MAP increases. When the engine isnot running, the manifold pressure gauge indicatesambient air pressure (i.e., 29.92 in. Hg). When theengine is started, the manifold pressure indication willdecrease to a value less than ambient pressure (i.e., idleat 12 in. Hg). Correspondingly, engine failure or powerloss is indicated on the manifold gauge as an increasein manifold pressure to a value corresponding to theambient air pressure at the altitude where the failureoccurred. [Figure 5-6]

The manifold pressure gauge is color-coded to indicatethe engine’s operating range. The face of the manifoldpressure gauge contains a green arc to show the normaloperating range, and a red radial line to indicate theupper limit of manifold pressure.

For any given r.p.m., there is a manifold pressure thatshould not be exceeded. If manifold pressure isexcessive for a given r.p.m., the pressure within thecylinders could be exceeded, thus placing undue stresson the cylinders. If repeated too frequently, this stresscould weaken the cylinder components, and eventuallycause engine failure.

Manifold Absolute Pressure (MAP)—The absolute pressure of thefuel/air mixture within the intake manifold, usually indicated in inchesof mercury.

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You can avoid conditions that could overstress thecylinders by being constantly aware of the r.p.m.,especially when increasing the manifold pressure.Conform to the manufacturer’s recommendations forpower settings of a particular engine so as to maintainthe proper relationship between manifold pressureand r.p.m.

When both manifold pressure and r.p.m. need to bechanged, avoid engine overstress by making poweradjustments in the proper order:

• When power settings are being decreased, reducemanifold pressure before reducing r.p.m. If r.p.m. isreduced before manifold pressure, manifoldpressure will automatically increase and possiblyexceed the manufacturer’s tolerances.

• When power settings are being increased,reverse the order—increase r.p.m. first, thenmanifold pressure.

• To prevent damage to radial engines, operating timeat maximum r.p.m. and manifold pressure must beheld to a minimum, and operation at maximumr.p.m. and low manifold pressure must be avoided.

Under normal operating conditions, the most severewear, fatigue, and damage to high performancereciprocating engines occurs at high r.p.m. and lowmanifold pressure.

INDUCTION SYSTEMSThe induction system brings in air from the outside,mixes it with fuel, and delivers the fuel/air mixture tothe cylinder where combustion occurs. Outside airenters the induction system through an intake port onthe front of the engine cowling. This port normally con-tains an air filter that inhibits the entry of dust and otherforeign objects. Since the filter may occasionally

become clogged, an alternate source of air must beavailable. Usually, the alternate air comes from insidethe engine cowling, where it bypasses a cloggedair filter. Some alternate air sources functionautomatically, while others operate manually.

Two types of induction systems are commonly used insmall airplane engines:

1. the carburetor system, which mixes the fuel andair in the carburetor before this mixture enters theintake manifold, and

2. the fuel injection system, which mixes the fueland air just before entry into each cylinder.

CARBURETOR SYSTEMSCarburetors are classified as either float-type orpressure-type. Pressure carburetors are usually notfound on small airplanes. The basic difference betweena pressure carburetor and a float-type is the pressurecarburetor delivers fuel under pressure by a fuel pump.

In the operation of the float-type carburetor system, theoutside air first flows through an air filter, usuallylocated at an air intake in the front part of the enginecowling. This filtered air flows into the carburetor andthrough a venturi, a narrow throat in the carburetor.When the air flows through the venturi, a low-pressurearea is created, which forces the fuel to flow through amain fuel jet located at the throat. The fuel then flowsinto the airstream, where it is mixed with the flowingair. See figure 5-7 on page 5-6.

The fuel/air mixture is then drawn through the intakemanifold and into the combustion chambers, where it isignited. The “float-type carburetor” acquires its namefrom a float, which rests on fuel within the floatchamber. A needle attached to the float opens andcloses an opening at the bottom of the carburetor bowl.This meters the correct amount of fuel into thecarburetor, depending upon the position of the float,which is controlled by the level of fuel in the floatchamber. When the level of the fuel forces the float torise, the needle valve closes the fuel opening and shutsoff the fuel flow to the carburetor. The needle valveopens again when the engine requires additional fuel.The flow of the fuel/air mixture to the combustionchambers is regulated by the throttle valve, which iscontrolled by the throttle in the cockpit.

MIXTURE CONTROLCarburetors are normally calibrated at sea-levelpressure, where the correct fuel-to-air mixture ratio isestablished with the mixture control set in the FULLRICH position. However, as altitude increases, thedensity of air entering the carburetor decreases, whilethe density of the fuel remains the same. This creates a

Figure 5-6. Engine power output is indicated on the manifoldpressure gauge.

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progressively richer mixture, which can result inengine roughness and an appreciable loss of power. Theroughness normally is due to spark plug fouling fromexcessive carbon buildup on the plugs. Carbon buildupoccurs because the excessively rich mixture lowers thetemperature inside the cylinder, inhibiting completecombustion of the fuel. This condition may occurduring the pretakeoff runup at high-elevation airportsand during climbs or cruise flight at high altitudes. Tomaintain the correct fuel/air mixture, you must lean themixture using the mixture control. Leaning the mixturedecreases fuel flow, which compensates for thedecreased air density at high altitude.

During a descent from high altitude, the opposite istrue. The mixture must be enriched, or it may becometoo lean. An overly lean mixture causes detonation,which may result in rough engine operation,overheating, and a loss of power. The best way tomaintain the proper mixture is to monitor the enginetemperature and enrichen the mixture as needed.Proper mixture control and better fuel economy forfuel-injected engines can be achieved by use of anexhaust gas temperature gauge. Since the process ofadjusting the mixture can vary from one airplane toanother, it is important to refer to the Airplane FlightManual (AFM) or the Pilot’s Operating Handbook(POH) to determine the specific procedures for agiven airplane.

CARBURETOR ICINGOne disadvantage of the float-type carburetor is itsicing tendency. Carburetor ice occurs due to the effectof fuel vaporization and the decrease in air pressure inthe venturi, which causes a sharp temperature drop inthe carburetor. If water vapor in the air condenses whenthe carburetor temperature is at or below freezing, icemay form on internal surfaces of the carburetor,including the throttle valve. [Figure 5-8]

FUEL/AIR MIXTUREThe blend of fuel and air is routedto the combustion chambers to beburned.

THROTTLE VALVEThe flow of the fuel/air mixture iscontrolled by the throttle valve. Thethrottle valve is adjusted from thecockpit by the throttle.

DISCHARGE NOZZLEFuel is forced through thedischarge nozzle into the venturiby greater atmosphericpressure in the float chamber.

VENTURIThe shape of the venturi createsan area of low pressure.

AIR INLETAir enters the carburetorthrough the air inlet.

AIR BLEEDThe air bleed allows air to be mixed with fuel beingdrawn out of the discharge nozzle to decreasefuel density and promote fuel vaporization.

FUEL INLETFuel is received intothe carburetor throughthe fuel inlet.

FLOAT CHAMBERFuel level is maintainedby a float-type device.

FUEL

MIXTURE NEEDLEThe mixture needle controls fuel tothe discharge nozzle. Mixture needleposition can be adjusted using themixture control.

Figure 5-7. Float-type carburetor.

To Engine

Incoming Air

Ice

Ice

Venturi

Fuel/AirMixture

Ice

Figure 5-8. The formation of carburetor ice may reduce orblock fuel/air flow to the engine.

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The reduced air pressure, as well as the vaporization offuel, contributes to the temperature decrease in thecarburetor. Ice generally forms in the vicinity of thethrottle valve and in the venturi throat. This restrictsthe flow of the fuel/air mixture and reduces power. Ifenough ice builds up, the engine may cease to operate.

Carburetor ice is most likely to occur whentemperatures are below 70°F (21°C) and the relativehumidity is above 80 percent. However, due to thesudden cooling that takes place in the carburetor, icingcan occur even with temperatures as high as 100°F(38°C) and humidity as low as 50 percent. Thistemperature drop can be as much as 60 to 70°F.Therefore, at an outside air temperature of 100°F, atemperature drop of 70°F results in an air temperaturein the carburetor of 30°F. [Figure 5-9]

The first indication of carburetor icing in an airplanewith a fixed-pitch propeller is a decrease in enginer.p.m., which may be followed by engine roughness. Inan airplane with a constant-speed propeller, carburetoricing usually is indicated by a decrease in manifoldpressure, but no reduction in r.p.m. Propeller pitch isautomatically adjusted to compensate for loss ofpower. Thus, a constant r.p.m. is maintained. Althoughcarburetor ice can occur during any phase of flight, it isparticularly dangerous when using reduced powerduring a descent. Under certain conditions, carburetorice could build unnoticed until you try to add power. Tocombat the effects of carburetor ice, engines withfloat-type carburetors employ a carburetor heat system.

CARBURETOR HEATCarburetor heat is an anti-icing system that preheatsthe air before it reaches the carburetor. Carburetor heatis intended to keep the fuel/air mixture above thefreezing temperature to prevent the formationof carburetor ice. Carburetor heat can be used to meltice that has already formed in the carburetorprovided that the accumulation is not too great. The

emphasis, however, is on using carburetor heat as apreventative measure.

The carburetor heat should be checked during theengine runup. When using carburetor heat, follow themanufacturer’s recommendations.

When conditions are conducive to carburetor icingduring flight, periodic checks should be made to detectits presence. If detected, full carburetor heat should beapplied immediately, and it should be left in the ONposition until you are certain that all the ice has beenremoved. If ice is present, applying partial heat orleaving heat on for an insufficient time might aggravatethe situation. In extreme cases of carburetor icing, evenafter the ice has been removed, full carburetor heatshould be used to prevent further ice formation. Acarburetor temperature gauge, if installed, is veryuseful in determining when to use carburetor heat.

Whenever the throttle is closed during flight, theengine cools rapidly and vaporization of the fuel is lesscomplete than if the engine is warm. Also, in thiscondition, the engine is more susceptible to carburetoricing. Therefore, if you suspect carburetor icingconditions and anticipate closed-throttle operation,adjust the carburetor heat to the full ON position beforeclosing the throttle, and leave it on during theclosed-throttle operation. The heat will aid invaporizing the fuel, and help prevent the formation ofcarburetor ice. Periodically, open the throttle smoothlyfor a few seconds to keep the engine warm, otherwisethe carburetor heater may not provide enough heat toprevent icing.

The use of carburetor heat causes a decrease in enginepower, sometimes up to 15 percent, because the heatedair is less dense than the outside air that had beenentering the engine. This enriches the mixture. Whenice is present in an airplane with a fixed-pitch propellerand carburetor heat is being used, there is a decrease inr.p.m., followed by a gradual increase in r.p.m. as theice melts. The engine also should run more smoothlyafter the ice has been removed. If ice is not present, ther.p.m. will decrease, then remain constant. Whencarburetor heat is used on an airplane with aconstant-speed propeller, and ice is present, a decreasein the manifold pressure will be noticed, followed by agradual increase. If carburetor icing is not present, thegradual increase in manifold pressure will not beapparent until the carburetor heat is turned off.

It is imperative that a pilot recognizes carburetor icewhen it forms during flight. In addition, a loss ofpower, altitude, and/or airspeed will occur. Thesesymptoms may sometimes be accompanied byvibration or engine roughness. Once a power loss isnoticed, immediate action should be taken to eliminate

Rel

ativ

e H

umid

ity

20°F(-7°C)

32°F(0°C)

70°F(21°C)

100°F(38°C)

100%

50%

80%

60%

70%

90%High Carburetor

Icing Potential

Carburetor Icing Possible

Outside Air Temperature

Figure 5-9. Although carburetor ice is most likely to formwhen the temperature and humidity are in ranges indicatedby this chart, carburetor ice is possible under conditionsnot depicted.

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ice already formed in the carburetor, and to preventfurther ice formation. This is accomplished byapplying full carburetor heat, which will cause afurther reduction in power, and possibly engineroughness as melted ice goes through the engine. Thesesymptoms may last from 30 seconds to severalminutes, depending on the severity of the icing. Duringthis period, the pilot must resist the temptation todecrease the carburetor heat usage. Carburetor heatmust remain in the full-hot position until normalpower returns.

Since the use of carburetor heat tends to reduce theoutput of the engine and also to increase the operatingtemperature, carburetor heat should not be used whenfull power is required (as during takeoff) or duringnormal engine operation, except to check for thepresence or to remove carburetor ice.

CARBURETOR AIR TEMPERATURE GAUGESome airplanes are equipped with a carburetor airtemperature gauge, which is useful in detectingpotential icing conditions. Usually, the face of thegauge is calibrated in degrees Celsius (°C), with ayellow arc indicating the carburetor air temperatureswhere icing may occur. This yellow arc typicallyranges between -15°C and +5°C (5°F and 41°F). If theair temperature and moisture content of the air are suchthat carburetor icing is improbable, the engine can beoperated with the indicator in the yellow range with noadverse effects. However, if the atmospheric conditionsare conducive to carburetor icing, the indicator must bekept outside the yellow arc by application ofcarburetor heat.

Certain carburetor air temperature gauges have a redradial, which indicates the maximum permissiblecarburetor inlet air temperature recommended by theengine manufacturer; also, a green arc may be includedto indicate the normal operating range.

OUTSIDE AIR TEMPERATURE GAUGEMost airplanes also are equipped with an outside airtemperature (OAT) gauge calibrated in both degreesCelsius and Fahrenheit. It provides the outside orambient air temperature for calculating trueairspeed, and also is useful in detecting potentialicing conditions.

FUEL INJECTION SYSTEMSIn a fuel injection system, the fuel is injected eitherdirectly into the cylinders, or just ahead of the intakevalve. A fuel injection system is considered to be lesssusceptible to icing than the carburetor system. Impacticing on the air intake, however, is a possibility ineither system. Impact icing occurs when ice forms onthe exterior of the airplane, and blocks openings suchas the air intake for the injection system.

The air intake for the fuel injection system is similar tothat used in the carburetor system, with an alternate airsource located within the engine cowling. This sourceis used if the external air source is obstructed. Thealternate air source is usually operated automatically,with a backup manual system that can be used if theautomatic feature malfunctions.

A fuel injection system usually incorporates these basiccomponents—an engine-driven fuel pump, a fuel/aircontrol unit, fuel manifold (fuel distributor), dischargenozzles, an auxiliary fuel pump, and fuel pressure/flowindicators. [Figure 5-10]

The auxiliary fuel pump provides fuel under pressureto the fuel/air control unit for engine starting and/oremergency use. After starting, the engine-driven fuelpump provides fuel under pressure from the fuel tankto the fuel/air control unit. This control unit, whichessentially replaces the carburetor, meters fuel basedon the mixture control setting, and sends it to the fuelmanifold valve at a rate controlled by the throttle. Afterreaching the fuel manifold valve, the fuel is distributedto the individual fuel discharge nozzles. The dischargenozzles, which are located in each cylinder head, injectthe fuel/air mixture directly into each cylinderintake port.

Some of the advantages of fuel injection are:

• Reduction in evaporative icing.

• Better fuel flow.

• Faster throttle response.

• Precise control of mixture.

• Better fuel distribution.

• Easier cold weather starts.

FuelManifoldValve

FuelDischargeNozzle

Fuel/AirControlUnit

Engine-DrivenFuel Pump

Fuel Tank

AuxiliaryFuel Pump

Figure 5-10. Fuel injection system.

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Disadvantages usually include:

• Difficulty in starting a hot engine.

• Vapor locks during ground operations onhot days.

• Problems associated with restarting an enginethat quits because of fuel starvation.

SUPERCHARGERS ANDTURBOSUPERCHARGERSTo increase an engine’s horsepower, manufacturershave developed supercharger and turbosuperchargersystems that compress the intake air to increase itsdensity. Airplanes with these systems have a manifoldpressure gauge, which displays manifold absolutepressure (MAP) within the engine’s intake manifold.

On a standard day at sea level with the engine shutdown, the manifold pressure gauge will indicate theambient absolute air pressure of 29.92 in. Hg. Becauseatmospheric pressure decreases approximately 1 in. Hgper 1,000 feet of altitude increase, the manifoldpressure gauge will indicate approximately 24.92 in.Hg at an airport that is 5,000 feet above sea level withstandard day conditions.

As a normally aspirated aircraft climbs, it eventuallyreaches an altitude where the MAP is insufficient for anormal climb. That altitude limit is the aircraft’sservice ceiling, and it is directly affected by theengine’s ability to produce power. If the induction airentering the engine is pressurized, or boosted, by eithera supercharger or a turbosupercharger, the aircraft’sservice ceiling can be increased. With these systems,you can fly at higher altitudes with the advantage ofhigher true airspeeds and the increased ability tocircumnavigate adverse weather.

SUPERCHARGERSA supercharger is an engine-driven air pump orcompressor that increases manifold pressure and forcesthe fuel/air mixture into the cylinders. The higher themanifold pressure, the more dense the fuel/air mixture,and the more power an engine can produce. With anormally aspirated engine, it is not possible to havemanifold pressure higher than the existing atmosphericpressure. A supercharger is capable of boostingmanifold pressure above 30 in. Hg.

The components in a supercharged induction systemare similar to those in a normally aspirated system, withthe addition of a supercharger between the fuelmetering device and intake manifold. A supercharger isdriven by the engine through a gear train at one speed,two speeds, or variable speeds. In addition,superchargers can have one or more stages. Each stageprovides an increase in pressure. Therefore,superchargers may be classified as single stage, twostage, or multistage, depending on the number of timescompression occurs.

An early version of a single-stage, single-speedsupercharger may be referred to as a sea-levelsupercharger. An engine equipped with this type ofsupercharger is called a sea-level engine. With thistype of supercharger, a single gear-driven impeller isused to increase the power produced by an engine at allaltitudes. The drawback, however, is that with this typeof supercharger, engine power output still decreaseswith an increase in altitude, in the same way that it doeswith a normally aspirated engine.

Single-stage, single-speed superchargers are found onmany high-powered radial engines, and use an airintake that faces forward so the induction system cantake full advantage of the ram air. Intake air passesthrough ducts to a carburetor, where fuel is metered inproportion to the airflow. The fuel/air charge is thenducted to the supercharger, or blower impeller, whichaccelerates the fuel/air mixture outward. Onceaccelerated, the fuel/air mixture passes through adiffuser, where air velocity is traded for pressureenergy. After compression, the resulting high pressurefuel/air mixture is directed to the cylinders.

Some of the large radial engines developed duringWorld War II have a single-stage, two-speedsupercharger. With this type of supercharger, a singleimpeller may be operated at two speeds. The lowimpeller speed is often referred to as the low blowersetting, while the high impeller speed is called the highblower setting. On engines equipped with a two-speedsupercharger, a lever or switch in the cockpit activatesan oil-operated clutch that switches from one speed tothe other.

Under normal operations, takeoff is made with thesupercharger in the low blower position. In this mode,the engine performs as a ground-boosted engine, andthe power output decreases as the aircraft gainsaltitude. However, once the aircraft reaches a specifiedaltitude, a power reduction is made, and thesupercharger control is switched to the high blowerposition. The throttle is then reset to the desired

Service Ceiling—The maximum density altitude where the best rate-of-climb airspeed will produce a 100 feet-per-minute climb at maximumweight while in a clean configuration with maximum continuous power.

Supercharger—An engine-driven air compressor used to provideadditional pressure to the induction air so the engine can produce addi-tional power.

Sea-Level Engine—A reciprocating aircraft engine having a ratedtakeoff power that is producible only at sea level.

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manifold pressure. An engine equipped with this typeof supercharger is called an altitude engine.[Figure 5-11]

TURBOSUPERCHARGERSThe most efficient method of increasing horsepower ina reciprocating engine is by use of a turbosupercharger,or turbocharger, as it is usually called. A drawback ofgear-driven superchargers is that they use a largeamount of the engine’s power output for the amount ofpower increase they produce. This problem is avoidedwith a turbocharger, because turbochargers arepowered by an engine’s exhaust gases. This means aturbocharger recovers energy from hot exhaust gasesthat would otherwise be lost.

Another advantage of turbochargers is that they can becontrolled to maintain an engine’s rated sea-levelhorsepower from sea level up to the engine’s criticalaltitude. Critical altitude is the maximum altitude atwhich a turbocharged engine can produce its ratedhorsepower. Above the critical altitude, power outputbegins to decrease like it does for a normally aspiratedengine.

Turbochargers increase the pressure of the engine’sinduction air, which allows the engine to develop sealevel or greater horsepower at higher altitudes. Aturbocharger is comprised of two main elements—a

turbine and a compressor. The compressor sectionhouses an impeller that turns at a high rate of speed. Asinduction air is drawn across the impeller blades, theimpeller accelerates the air, allowing a large volume ofair to be drawn into the compressor housing. Theimpeller’s action subsequently produces high-pressure,high-density air, which is delivered to the engine. Toturn the impeller, the engine’s exhaust gases are used todrive a turbine wheel that is mounted on the oppositeend of the impeller’s drive shaft. By directing differentamounts of exhaust gases to flow over the turbine,more energy can be extracted, causing the impeller todeliver more compressed air to the engine. The wastegate is used to vary the mass of exhaust gas flowinginto the turbine. A waste gate is essentially anadjustable butterfly valve that is installed in the exhaustsystem. When closed, most of the exhaust gases fromthe engine are forced to flow through the turbine. Whenopen, the exhaust gases are allowed to bypass theturbine by flowing directly out through the engine’sexhaust pipe. [Figure 5-12]

Since the temperature of a gas rises when it iscompressed, turbocharging causes the temperature ofthe induction air to increase. To reduce thistemperature and lower the risk of detonation, manyturbocharged engines use an intercooler. Anintercooler is a small heat exchanger that uses outsideair to cool the hot compressed air before it enters thefuel metering device.

SYSTEM OPERATIONOn most modern turbocharged engines, the position ofthe waste gate is governed by a pressure-sensingcontrol mechanism coupled to an actuator. Engine oildirected into or away from this actuator moves thewaste gate position. On these systems, the actuator isautomatically positioned to produce the desired MAPsimply by changing the position of the throttle control.

Other turbocharging system designs use a separatemanual control to position the waste gate. With manualcontrol, you must closely monitor the manifoldpressure gauge to determine when the desired MAP hasbeen achieved. Manual systems are often found onaircraft that have been modified with aftermarketturbocharging systems. These systems require specialoperating considerations. For example, if the wastegate is left closed after descending from a high altitude,it is possible to produce a manifold pressure thatexceeds the engine’s limitations. This condition is

Brake

Horsepower

S.L. Density Altitude

Normally Aspirated Engine

High BlowerLow Blower

Two SpeedSuperchargedEngine

Figure 5-11. Power output of normally aspirated engine com-pared to a single-stage, two-speed supercharged engine.

Altitude Engine—A reciprocating aircraft engine having a rated takeoffpower that is producible from sea level to an established higher altitude.

Turbocharger—An air compressor driven by exhaust gases, whichincreases the pressure of the air going into the engine through thecarburetor or fuel injection system.

Waste Gate—A controllable valve in the exhaust system of areciprocating engine equipped with a turbocharger. The valve iscontrolled to vary the amount of exhaust gases forced through theturbocharger turbine.

Intercooler—A device used to remove heat from air or liquid.

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referred to as an overboost, and it may produce severedetonation because of the leaning effect resulting fromincreased air density during descent.

Although an automatic waste gate system is less likelyto experience an overboost condition, it can still occur.If you try to apply takeoff power while the engine oiltemperature is below its normal operating range, thecold oil may not flow out of the waste gate actuatorquickly enough to prevent an overboost. To helpprevent overboosting, you should advance the throttlecautiously to prevent exceeding the maximummanifold pressure limits.

There are system limitations that you should be awareof when flying an aircraft with a turbocharger. Forinstance, a turbocharger turbine and impeller canoperate at rotational speeds in excess of 80,000 r.p.m.while at extremely high temperatures. To achieve highrotational speed, the bearings within the system mustbe constantly supplied with engine oil to reduce thefrictional forces and high temperature. To obtainadequate lubrication, the oil temperature should be inthe normal operating range before high throttle settingsare applied. In addition, you should allow theturbocharger to cool and the turbine to slow downbefore shutting the engine down. Otherwise, the oilremaining in the bearing housing will boil, causinghard carbon deposits to form on the bearings and shaft.These deposits rapidly deteriorate the turbocharger’sefficiency and service life. For further limitations, referto the AFM/POH.

HIGH ALTITUDE PERFORMANCEAs an aircraft equipped with a turbocharging systemclimbs, the waste gate is gradually closed to maintainthe maximum allowable manifold pressure. At somepoint, however, the waste gate will be fully closed, andwith further increases in altitude, the manifold pressurewill begin to decrease. This is the critical altitude,which is established by the airplane or enginemanufacturer. When evaluating the performance of theturbocharging system, if the manifold pressure beginsdecreasing before the specified critical altitude, theengine and turbocharging system should be inspectedby a qualified aviation maintenance technician toverify the system’s proper operation.

IGNITION SYSTEMThe ignition system provides the spark that ignites thefuel/air mixture in the cylinders and is made up ofmagnetos, spark plugs, high-tension leads, and theignition switch. [Figure 5-13]

Exhaust GasDischarge Waste Gate

This controls the amount of exhaustthrough the turbine. Waste gate positionis actuated by engine oil pressure.

TurbochargerThe turbocharger incorporates aturbine, which is driven by exhaustgases, and a compressor thatpressurizes the incoming air.

Throttle BodyThis regulates airflow to the engine.

Intake ManifoldPressurized air from theturbocharger is suppliedto the cylinders.

Exhaust ManifoldExhaust gas is ducted throughthe exhaust manifold and isused to turn the turbine whichdrives the compressor.

Air IntakeIntake air is ducted to the turbochargerwhere it is compressed.

Figure 5-12.Turbocharger components.

Overboost—A condition in which a reciprocating engine has exceededthe maximum manifold pressure allowed by the manufacturer.

OFFR L BOTH

START

UpperMagneto Wires

LowerMagneto Wires

UpperSparkPlugs

Lower SparkPlugs

Left Magneto Right Magneto

LowerSparkPlugs

UpperSparkPlugs

2

3

1

4

Figure 5-13. Ignition system components.

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A magneto uses a permanent magnet to generate anelectrical current completely independent of theaircraft’s electrical system. The magneto generatessufficiently high voltage to jump a spark across thespark plug gap in each cylinder. The system begins tofire when you engage the starter and the crankshaftbegins to turn. It continues to operate whenever thecrankshaft is rotating.

Most standard certificated airplanes incorporate a dualignition system with two individual magnetos, separatesets of wires, and spark plugs to increase reliabilityof the ignition system. Each magneto operatesindependently to fire one of the two spark plugs in eachcylinder. The firing of two spark plugs improvescombustion of the fuel/air mixture and results in aslightly higher power output. If one of the magnetosfails, the other is unaffected. The engine will continueto operate normally, although you can expect a slightdecrease in engine power. The same is true if one of thetwo spark plugs in a cylinder fails.

The operation of the magneto is controlled in thecockpit by the ignition switch. The switch hasfive positions:

1. OFF

2. R—Right

3. L—Left

4. BOTH

5. START

With RIGHT or LEFT selected, only the associatedmagneto is activated. The system operates on bothmagnetos with BOTH selected.

You can identify a malfunctioning ignition systemduring the pretakeoff check by observing the decreasein r.p.m. that occurs when you first move the ignitionswitch from BOTH to RIGHT, and then from BOTH toLEFT. A small decrease in engine r.p.m. is normalduring this check. The permissible decrease is listed inthe AFM or POH. If the engine stops running when youswitch to one magneto or if the r.p.m. drop exceeds theallowable limit, do not fly the airplane until theproblem is corrected. The cause could be fouled plugs,broken or shorted wires between the magneto and theplugs, or improperly timed firing of the plugs. It shouldbe noted that “no drop” in r.p.m. is not normal, and inthat instance, the airplane should not be flown.

Following engine shutdown, turn the ignition switch tothe OFF position. Even with the battery and masterswitches OFF, the engine can fire and turn over if youleave the ignition switch ON and the propeller ismoved because the magneto requires no outside sourceof electrical power. The potential for serious injury inthis situation is obvious.

Loose or broken wires in the ignition system also cancause problems. For example, if the ignition switch isOFF, the magneto may continue to fire if the ignitionswitch ground wire is disconnected. If this occurs, theonly way to stop the engine is to move themixture lever to the idle cutoff position, then have thesystem checked by a qualified aviation maintenancetechnician.

COMBUSTIONDuring normal combustion, the fuel/air mixture burnsin a very controlled and predictable manner. Althoughthe process occurs in a fraction of a second, the mixtureactually begins to burn at the point where it is ignitedby the spark plugs, then burns away from the plugsuntil it is all consumed. This type of combustion causesa smooth buildup of temperature and pressure andensures that the expanding gases deliver the maximumforce to the piston at exactly the right time in the powerstroke. [Figure 5-14]

Detonation is an uncontrolled, explosive ignition ofthe fuel/air mixture within the cylinder’s combustionchamber. It causes excessive temperatures andpressures which, if not corrected, can quickly lead tofailure of the piston, cylinder, or valves. In less severecases, detonation causes engine overheating,roughness, or loss of power.

Detonation is characterized by high cylinder headtemperatures, and is most likely to occur whenoperating at high power settings. Some commonoperational causes of detonation include:

Magneto—A self-contained, engine-driven unit that supplies electricalcurrent to the spark plugs; completely independent of the airplane’selectrical system. Normally, there are two magnetos per engine.

Normal Combustion Explosion

Figure 5-14. Normal combustion and explosive combustion.

Detonation—An uncontrolled, explosive ignition of the fuel/air mixturewithin the cylinder’s combustion chamber.

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• Using a lower fuel grade than that specified bythe aircraft manufacturer.

• Operating with extremely high manifoldpressures in conjunction with low r.p.m.

• Operating the engine at high power settings withan excessively lean mixture.

• Detonation also can be caused by extendedground operations, or steep climbs where cylinder cooling is reduced.

Detonation may be avoided by following these basicguidelines during the various phases of ground andflight operations:

• Make sure the proper grade of fuel is being used.

• While on the ground, keep the cowl flaps (ifavailable) in the full-open position to provide themaximum airflow through the cowling.

• During takeoff and initial climb, the onset ofdetonation can be reduced by using an enrichedfuel mixture, as well as using a shallower climbangle to increase cylinder cooling.

• Avoid extended, high power, steep climbs.

• Develop a habit of monitoring the engineinstruments to verify proper operation accordingto procedures established by the manufacturer.

Preignition occurs when the fuel/air mixture ignitesprior to the engine’s normal ignition event. Prematureburning is usually caused by a residual hot spot in thecombustion chamber, often created by a small carbondeposit on a spark plug, a cracked spark plug insulator,or other damage in the cylinder that causes a part toheat sufficiently to ignite the fuel/air charge.Preignition causes the engine to lose power, andproduces high operating temperature. As withdetonation, preignition may also cause severeengine damage, because the expanding gases exertexcessive pressure on the piston while still on itscompression stroke.

Detonation and preignition often occur simultaneouslyand one may cause the other. Since either conditioncauses high engine temperature accompanied by adecrease in engine performance, it is often difficult todistinguish between the two. Using the recommendedgrade of fuel and operating the engine within its propertemperature, pressure, and r.p.m. ranges reduce thechance of detonation or preignition.

FUEL SYSTEMSThe fuel system is designed to provide an uninterruptedflow of clean fuel from the fuel tanks to the engine. Thefuel must be available to the engine under allconditions of engine power, altitude, attitude, andduring all approved flight maneuvers. Two commonclassifications apply to fuel systems in smallairplanesgravity-feed and fuel-pump systems.

The gravity-feed system utilizes the force of gravity totransfer the fuel from the tanks to the engineforexample, on high-wing airplanes where the fuel tanksare installed in the wings. This places the fuel tanksabove the carburetor, and the fuel is gravity fed throughthe system and into the carburetor. If the design of theairplane is such that gravity cannot be used to transferfuel, fuel pumps are installedfor example, onlow-wing airplanes where the fuel tanks in the wingsare located below the carburetor. [Figure 5-15]

Preignition—The uncontrolled combustion of the fuel/air mixture inadvance of the normal ignition.

Selector Valve

Strainer

Carburetor

Primer

Left Tank Right Tank

Left Tank Right Tank

Selector Valve

FUEL-PUMP SYSTEM

GRAVITY-FEED SYSTEM

Vent

Strainer

Engine-Driven Pump

Electric Pump

Primer

Carburetor

Figure 5-15. Gravity-feed and fuel-pump systems.

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FUEL PUMPSAirplanes with fuel pump systems have two fuelpumps. The main pump system is engine driven, and anelectrically driven auxiliary pump is provided for usein engine starting and in the event the engine pumpfails. The auxiliary pump, also known as a boost pump,provides added reliability to the fuel system. Theelectrically driven auxiliary pump is controlled by aswitch in the cockpit.

FUEL PRIMERBoth gravity fed and pump systems may incorporate afuel primer into the system. The primer is used to drawfuel from the tanks to vaporize it directly into thecylinders prior to starting the engine. This isparticularly helpful during cold weather, when enginesare hard to start because there is not enough heatavailable to vaporize the fuel in the carburetor. It isimportant to lock the primer in place when it is not inuse. If the knob is free to move, it may vibrate outduring flight and can cause an excessively richmixture. To avoid overpriming, read the priminginstructions for your airplane.

FUEL TANKSThe fuel tanks, normally located inside the wings of anairplane, have a filler opening on top of the wingthrough which they can be filled. A filler cap coversthis opening. The tanks are vented to the outside tomaintain atmospheric pressure inside the tank. Theymay be vented through the filler cap or through a tubeextending through the surface of the wing. Fuel tanksalso include an overflow drain that may stand alone orbe collocated with the fuel tank vent. This allows fuelto expand with increases in temperature withoutdamage to the tank itself. If the tanks have been filledon a hot day, it is not unusual to see fuel coming fromthe overflow drain.

FUEL GAUGESThe fuel quantity gauges indicate the amount of fuelmeasured by a sensing unit in each fuel tank and isdisplayed in gallons or pounds. Aircraft certificationrules only require accuracy in fuel gauges when theyread “empty.” Any reading other than “empty” shouldbe verified. Do not depend solely on the accuracy ofthe fuel quantity gauges. Always visually check thefuel level in each tank during the preflight inspection,and then compare it with the corresponding fuelquantity indication.

If a fuel pump is installed in the fuel system, a fuelpressure gauge is also included. This gauge indicatesthe pressure in the fuel lines. The normal operatingpressure can be found in the AFM/POH, or on thegauge by color coding.

FUEL SELECTORSThe fuel selector valve allows selection of fuel fromvarious tanks. A common type of selector valvecontains four positions: LEFT, RIGHT, BOTH, andOFF. Selecting the LEFT or RIGHT position allowsfuel to feed only from that tank, while selecting theBOTH position feeds fuel from both tanks. The LEFTor RIGHT position may be used to balance the amountof fuel remaining in each wing tank. [Figure 5-16]

Fuel placards will show any limitations on fuel tankusage, such as “level flight only” and/or “both” forlandings and takeoffs.

Regardless of the type of fuel selector in use, fuelconsumption should be monitored closely to ensurethat a tank does not run completely out of fuel. Runninga fuel tank dry will not only cause the engine to stop,but running for prolonged periods on one tank causesan unbalanced fuel load between tanks. Running a tankcompletely dry may allow air to enter the fuel system,which may cause vapor lock. When this situationdevelops, it may be difficult to restart the engine. Onfuel-injected engines, the fuel may become so hot itvaporizes in the fuel line, not allowing fuel to reachthe cylinders.

FUEL STRAINERS, SUMPS, AND DRAINSAfter the fuel selector valve, the fuel passes through astrainer before it enters the carburetor. This strainerremoves moisture and other sediments that might be inthe system. Since these contaminants are heavier thanaviation fuel, they settle in a sump at the bottom of thestrainer assembly. A sump is defined as a low point in afuel system and/or fuel tank. The fuel system maycontain sump, fuel strainer, and fuel tank drains, someof which may be collocated.

The fuel strainer should be drained before each flight.Fuel samples should be drained and checked visually

Figure 5-16. Fuel selector valve.

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for water and contaminants. Water in the sump ishazardous because in cold weather the water can freezeand block fuel lines. In warm weather, it can flow intothe carburetor and stop the engine. If water is present inthe sump, it is likely there is more water in the fueltanks, and you should continue to drain them until thereis no evidence of water. In any event, never take offuntil you are certain that all water and contaminantshave been removed from the engine fuel system.

Because of the variation in fuel systems, you shouldbecome thoroughly familiar with the systems that applyto your airplane. Consult the AFM or POH for specificoperating procedures.

FUEL GRADESAviation gasoline, or AVGAS, is identified by anoctane or performance number (grade), whichdesignates the antiknock value or knock resistance ofthe fuel mixture in the engine cylinder. The higher thegrade of gasoline, the more pressure the fuel canwithstand without detonating. Lower grades of fuel areused in lower-compression engines because these fuelsignite at a lower temperature. Higher grades are used inhigher-compression engines, because they must igniteat higher temperatures, but not prematurely. If theproper grade of fuel is not available, use the next highergrade as a substitute. Never use a lower grade. This cancause the cylinder head temperature and engine oiltemperature to exceed their normal operating range,which may result in detonation.

Several grades of aviation fuel are available. Care mustbe exercised to ensure that the correct aviation grade isbeing used for the specific type of engine. The properfuel grade is stated in the AFM or POH, on placards inthe cockpit, and next to the filler caps. Due to its leadcontent, auto gas should NEVER be used in aircraftengines unless the aircraft has been modified with aSupplemental Type Certificate (STC) issued by theFederal Aviation Administration.

The current method to identify aviation gasoline foraircraft with reciprocating engines is by the octane andperformance number, along with the abbreviationAVGAS. These aircraft use AVGAS 80, 100, and100LL. Although AVGAS 100LL performs the same asgrade 100, the “LL” indicates it has a low lead content.Fuel for aircraft with turbine engines is classified asJET A, JET A-1, and JET B. Jet fuel is basicallykerosene and has a distinctive kerosene smell.

Since use of the correct fuel is critical, dyes areadded to help identify the type and grade of fuel.[Figure 5-17]

In addition to the color of the fuel itself, thecolor-coding system extends to decals and variousairport fuel handling equipment. For example, allaviation gasolines are identified by name, using whiteletters on a red background. In contrast, turbine fuelsare identified by white letters on a black background.

FUEL CONTAMINATIONOf the accidents attributed to powerplant failure fromfuel contamination, most have been traced to:

• Inadequate preflight inspection by the pilot.

• Servicing aircraft with improperly filtered fuelfrom small tanks or drums.

• Storing aircraft with partially filled fuel tanks.

• Lack of proper maintenance.

Fuel should be drained from the fuel strainer quickdrain and from each fuel tank sump into a transparentcontainer, and then checked for dirt and water. Whenthe fuel strainer is being drained, water in the tank maynot appear until all the fuel has been drained from thelines leading to the tank. This indicates that waterremains in the tank, and is not forcing the fuel out ofthe fuel lines leading to the fuel strainer. Therefore,drain enough fuel from the fuel strainer to be certainthat fuel is being drained from the tank. The amountwill depend on the length of fuel line from the tank tothe drain. If water or other contaminants are found inthe first sample, drain further samples until notrace appears.

80AVGAS

100AVGAS

RED

GREEN

AVGAS 80

AVGAS 100

100LLAVGAS

BLUEAVGAS 100LL

JETA

COLORLESSOR STRAW

JET A

FUEL TYPEAND GRADE

COLOR OFFUEL

EQUIPMENTCOLOR

Figure 5-17. Aviation fuel color-coding system.

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Water may also remain in the fuel tanks after thedrainage from the fuel strainer had ceased to show anytrace of water. This residual water can be removed onlyby draining the fuel tank sump drains.

Water is the principal fuel contaminant. Suspendedwater droplets in the fuel can be identified by a cloudyappearance of the fuel or by the clear separation ofwater from the colored fuel, which occurs after thewater has settled to the bottom of the tank. As a safetymeasure, the fuel sumps should be drained before everyflight during the preflight inspection.

Fuel tanks should be filled after each flight, or at leastafter the last flight of the day to prevent moisturecondensation within the tank. Another way to preventfuel contamination is to avoid refueling from cans anddrums. Refueling from cans or drums may result in fuelcontamination.

The use of a funnel and chamois skin when refuelingfrom cans or drums is hazardous under any conditions,and should be discouraged. In remote areas or inemergency situations, there may be no alternative torefueling from sources with inadequate anticontamina-tion systems, and a chamois and funnel may be the onlypossible means of filtering fuel. However, the use of achamois will not always ensure decontaminated fuel.Worn-out chamois will not filter water; neither will anew, clean chamois that is already water-wet or damp.Most imitation chamois skins will not filter water.

REFUELING PROCEDURESStatic electricity is formed by the friction of air passingover the surfaces of an airplane in flight and by the flowof fuel through the hose and nozzle during refueling.Nylon, dacron, or wool clothing is especially prone toaccumulate and discharge static electricity from theperson to the funnel or nozzle. To guard against thepossibility of static electricity igniting fuel fumes, aground wire should be attached to the aircraft beforethe fuel cap is removed from the tank. The refuelingnozzle then should be grounded to the aircraft beforerefueling is begun, and should remain groundedthroughout the refueling process. When a fuel truck isused, it should be grounded prior to the fuel nozzlecontacting the aircraft.

If fueling from drums or cans is necessary, properbonding and grounding connections are important.Drums should be placed near grounding posts, and thefollowing sequence of connections observed:

1. Drum to ground.

2. Ground to aircraft.

3. Drum to aircraft.

4. Nozzle to aircraft before the fuel cap is removed.

When disconnecting, reverse the order.

The passage of fuel through a chamois increases thecharge of static electricity and the danger of sparks. Theaircraft must be properly grounded and the nozzle,chamois filter, and funnel bonded to the aircraft. If acan is used, it should be connected to either thegrounding post or the funnel. Under no circumstancesshould a plastic bucket or similar nonconductivecontainer be used in this operation.

STARTING SYSTEMMost small aircraft use a direct-cranking electric startersystem. This system consists of a source of electricity,wiring, switches, and solenoids to operate the starterand a starter motor. Most aircraft have starters thatautomatically engage and disengage when operated,but some older aircraft have starters that aremechanically engaged by a lever actuated by the pilot.The starter engages the aircraft flywheel, rotating theengine at a speed that allows the engine to start andmaintain operation.

Electrical power for starting is usually supplied by anon-board battery, but can also be supplied by externalpower through an external power receptacle. When thebattery switch is turned on, electricity is supplied to themain power bus through the battery solenoid. Both thestarter and the starter switch draw current from the mainbus, but the starter will not operate until the startingsolenoid is energized by the starter switch being turnedto the “start” position. When the starter switch is releasedfrom the “start” position, the solenoid removes powerfrom the starter motor. The starter motor is protectedfrom being driven by the engine through a clutch in thestarter drive that allows the engine to run faster than thestarter motor. [Figure 5-18]

When starting an engine, the rules of safety andcourtesy should be strictly observed. One of the mostimportant is to make sure there is no one near thepropeller. In addition, the wheels should be chockedand the brakes set, to avoid hazards caused byunintentional movement. To avoid damage to thepropeller and property, the airplane should be in an areawhere the propeller will not stir up gravel or dust.

OIL SYSTEMSThe engine oil system performs several importantfunctions, including:

• Lubrication of the engine’s moving parts.

• Cooling of the engine by reducing friction.

• Removing heat from the cylinders.

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• Providing a seal between the cylinder wallsand pistons.

• Carrying away contaminants.

Reciprocating engines use either a wet-sump ordry-sump oil system. In a dry-sump system, the oil iscontained in a separate tank, and circulated through theengine by pumps. In a wet-sump system, the oil islocated in a sump, which is an integral part of theengine. [Figure 5-19]

The main component of a wet-sump system is the oilpump, which draws oil from the sump and routes it tothe engine. After the oil passes through the engine, itreturns to the sump. In some engines, additionallubrication is supplied by the rotating crankshaft,which splashes oil onto portions of the engine.

An oil pump also supplies oil pressure in a dry-sumpsystem, but the source of the oil is a separate oil tank,located external to the engine. After oil is routedthrough the engine, it is pumped from the variouslocations in the engine back to the oil tank by scavengepumps. Dry sump systems allow for a greater volumeof oil to be supplied to the engine, which makes themmore suitable for very large reciprocating engines.

The oil pressure gauge provides a direct indication ofthe oil system operation. It measures the pressure in

BatteryContactor(Solenoid)

StarterContactor

ExternalPowerRelay

++

To groundthroughmasterswitch

OFF

LR

B

S

STARTER

IGNITIONSWITCH

ExternalPowerPlug

MAIN

BUS

+

-

Figure 5-18.Typical starting circuit.

Pressure Oil From Oil Pump

OIL TEMP

Sump Oil and Return OilFrom Relief Valve

Low PressureOil Screen

Oil Coolerand Filter

Oil Sump

Engine and Accessory Bearings

Oil Filler Capand Dipstick

Oil Pressure Relief Valve

Oil PressureGauge

Oil Temperature Gauge

High Pressure Oil Screen

OIL PRESS

TOP VIEW

Oil Pump

OIL TEMP

100 245

OIL PRESS

0 60 115

Figure 5-19. Wet-sump oil system.

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pounds per square inch (p.s.i.) of the oil supplied to theengine. Green indicates the normal operating range,while red indicates the minimum and maximumpressures. There should be an indication of oil pressureduring engine start. Refer to the AFM/POH formanufacturer limitations.

The oil temperature gauge measures the temperature ofoil. A green area shows the normal operating range andthe red line indicates the maximum allowabletemperature. Unlike oil pressure, changes in oiltemperature occur more slowly. This is particularlynoticeable after starting a cold engine, when it may takeseveral minutes or longer for the gauge to show anyincrease in oil temperature.

Check oil temperature periodically during flightespecially when operating in high or low ambient airtemperature. High temperature indications mayindicate a plugged oil line, a low oil quantity, a blockedoil cooler, or a defective temperature gauge. Lowtemperature indications may indicate improper oilviscosity during cold weather operations.

The oil filler cap and dipstick (for measuring the oilquantity) are usually accessible through a panel in theengine cowling. If the quantity does not meet themanufacturer’s recommended operating levels, oilshould be added. The AFM, POH, or placards near theaccess panel provide information about the correct oiltype and weight, as well as the minimum and maximumoil quantity. [Figure 5-20]

ENGINE COOLING SYSTEMSThe burning fuel within the cylinders produces intenseheat, most of which is expelled through the exhaustsystem. Much of the remaining heat, however, must beremoved, or at least dissipated, to prevent the enginefrom overheating. Otherwise, the extremely highengine temperatures can lead to loss of power,excessive oil consumption, detonation, and seriousengine damage.

While the oil system is vital to internal cooling of theengine, an additional method of cooling is necessaryfor the engine’s external surface. Most small airplanesare air cooled, although some are liquid cooled.

Air cooling is accomplished by air flowing into theengine compartment through openings in front of theengine cowling. Baffles route this air over fins attachedto the engine cylinders, and other parts of the engine,where the air absorbs the engine heat. Expulsion of thehot air takes place through one or more openings in thelower, aft portion of the engine cowling. [Figure 5-21]

The outside air enters the engine compartment throughan inlet behind the propeller hub. Baffles direct it to thehottest parts of the engine, primarily the cylinders,which have fins that increase the area exposed tothe airflow.

The air cooling system is less effective during groundoperations, takeoffs, go-arounds, and other periods ofhigh-power, low-airspeed operation. Conversely,high-speed descents provide excess air and canshock-cool the engine, subjecting it to abrupttemperature fluctuations.

Figure 5-20. Always check the engine oil level during the pre-flight inspection.

Fixed CowlOpening

Baffle

Cylinders

AirInlet

Baffle

Figure 5-21. Outside air aids in cooling the engine.

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Operating the engine at higher than its designedtemperature can cause loss of power, excessive oilconsumption, and detonation. It will also lead toserious permanent damage, such as scoring thecylinder walls, damaging the pistons and rings, andburning and warping the valves. Monitoring thecockpit engine temperature instruments will aid inavoiding high operating temperature.

Under normal operating conditions in airplanes notequipped with cowl flaps, the engine temperature canbe controlled by changing the airspeed or the poweroutput of the engine. High engine temperatures can bedecreased by increasing the airspeed and/or reducingthe power.

The oil temperature gauge gives an indirect anddelayed indication of rising engine temperature, butcan be used for determining engine temperature if thisis the only means available.

Many airplanes are equipped with a cylinder-headtemperature gauge. This instrument indicates a directand immediate cylinder temperature change. Thisinstrument is calibrated in degrees Celsius orFahrenheit, and is usually color-coded with a green arcto indicate the normal operating range. A red line onthe instrument indicates maximum allowable cylinderhead temperature.

To avoid excessive cylinder head temperatures,increase airspeed, enrich the mixture, and/or reducepower. Any of these procedures help in reducing theengine temperature. On airplanes equipped withcowl flaps, use the cowl flap positions to control thetemperature. Cowl flaps are hinged covers that fit overthe opening through which the hot air is expelled. If theengine temperature is low, the cowl flaps can be closed,thereby restricting the flow of expelled hot air andincreasing engine temperature. If the enginetemperature is high, the cowl flaps can be opened topermit a greater flow of air through the system, therebydecreasing the engine temperature.

EXHAUST SYSTEMSEngine exhaust systems vent the burned combustiongases overboard, provide heat for the cabin, and defrostthe windscreen. An exhaust system has exhaust pipingattached to the cylinders, as well as a muffler and amuffler shroud. The exhaust gases are pushed out ofthe cylinder through the exhaust valve and then throughthe exhaust pipe system to the atmosphere.

For cabin heat, outside air is drawn into the air inletand is ducted through a shroud around the muffler. Themuffler is heated by the exiting exhaust gases and, inturn, heats the air around the muffler. This heated air isthen ducted to the cabin for heat and defrostapplications. The heat and defrost are controlled in thecockpit, and can be adjusted to the desired level.

Exhaust gases contain large amounts of carbonmonoxide, which is odorless and colorless. Carbonmonoxide is deadly, and its presence is virtuallyimpossible to detect. The exhaust system must be ingood condition and free of cracks.

Some exhaust systems have an exhaust gastemperature probe. This probe transmits the exhaustgas temperature (EGT) to an instrument in the cockpit.The EGT gauge measures the temperature of the gasesat the exhaust manifold. This temperature varies withthe ratio of fuel to air entering the cylinders and can beused as a basis for regulating the fuel/air mixture. TheEGT gauge is highly accurate in indicating the correctmixture setting. When using the EGT to aid in leaningthe fuel/air mixture, fuel consumption can be reduced.For specific procedures, refer to the manufacturer’srecommendations for leaning the mixture.

ELECTRICAL SYSTEMAirplanes are equipped with either a 14- or 28-voltdirect-current electrical system. A basic airplaneelectrical system consists of the following components:

• Alternator/generator

• Battery

• Master/battery switch

• Alternator/generator switch

• Bus bar, fuses, and circuit breakers

• Voltage regulator

• Ammeter/loadmeter

• Associated electrical wiring

Engine-driven alternators or generators supply electriccurrent to the electrical system. They also maintain asufficient electrical charge in the battery. Electricalenergy stored in a battery provides a source ofelectrical power for starting the engine and a limitedsupply of electrical power for use in the event thealternator or generator fails.

Cowl Flaps—Shutter-like devices arranged around certain air-cooledengine cowlings, which may be opened or closed to regulate the flow ofair around the engine.

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Most direct current generators will not produce asufficient amount of electrical current at low enginer.p.m. to operate the entire electrical system. Therefore,during operations at low engine r.p.m., the electricalneeds must be drawn from the battery, which canquickly be depleted.

Alternators have several advantages over generators.Alternators produce sufficient current to operate theentire electrical system, even at slower engine speeds,by producing alternating current, which is converted todirect current. The electrical output of an alternator ismore constant throughout a wide range of enginespeeds.

Some airplanes have receptacles to which an externalground power unit (GPU) may be connected to provideelectrical energy for starting. These are very useful,especially during cold weather starting. Follow themanufacturer’s recommendations for engine startingusing a GPU.

The electrical system is turned on or off with a masterswitch. Turning the master switch to the ON positionprovides electrical energy to all the electricalequipment circuits with the exception of the ignitionsystem. Equipment that commonly uses the electricalsystem for its source of energy includes:

• Position lights

• Anticollision lights

• Landing lights

• Taxi lights

• Interior cabin lights

• Instrument lights

• Radio equipment

• Turn indicator

• Fuel gauges

• Electric fuel pump

• Stall warning system

• Pitot heat

• Starting motor

Many airplanes are equipped with a battery switch thatcontrols the electrical power to the airplane in amanner similar to the master switch. In addition, analternator switch is installed which permits the pilot toexclude the alternator from the electrical system in theevent of alternator failure. [Figure 5-22]

With the alternator half of the switch in the OFFposition, the entire electrical load is placed on thebattery. Therefore, all nonessential electrical equipmentshould be turned off to conserve battery power.

A bus bar is used as a terminal in the airplane electricalsystem to connect the main electrical system to theequipment using electricity as a source of power. Thissimplifies the wiring system and provides a commonpoint from which voltage can be distributed throughoutthe system. [Figure 5-23]

Fuses or circuit breakers are used in the electrical systemto protect the circuits and equipment from electricaloverload. Spare fuses of the proper amperage limitshould be carried in the airplane to replace defective orblown fuses. Circuit breakers have the same function asa fuse but can be manually reset, rather than replaced, ifan overload condition occurs in the electrical system.Placards at the fuse or circuit breaker panel identify thecircuit by name and show the amperage limit.

An ammeter is used to monitor the performance of theairplane electrical system. The ammeter shows if thealternator/generator is producing an adequate supply ofelectrical power. It also indicates whether or not thebattery is receiving an electrical charge.

Ammeters are designed with the zero point in thecenter of the face and a negative or positive indicationon either side. [Figure 5-24] When the pointer of theammeter on the left is on the plus side, it shows thecharging rate of the battery. A minus indication meansmore current is being drawn from the battery than isbeing replaced. A full-scale minus deflection indicatesa malfunction of the alternator/generator. A full-scalepositive deflection indicates a malfunction of theregulator. In either case, consult the AFM or POH forappropriate action to be taken.

Figure 5-22. On this master switch, the left half is for thealternator and the right half is for the battery.

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Not all airplanes are equipped with an ammeter. Somehave a warning light that, when lighted, indicates adischarge in the system as a generator/alternatormalfunction. Refer to the AFM or POH for appropriateaction to be taken.

Another electrical monitoring indicator is a loadmeter.This type of gauge, illustrated on the right in figure5-24, has a scale beginning with zero and shows the loadbeing placed on the alternator/generator. The loadmeterreflects the total percentage of the load placed on the

PRIMARY

BUS

AVIONICS

BUS

To Fuel Quantity Indicators

To Flashing Beacon

To Pitot Heat

To Radio Cooling Fan

To Strobe Lights

To Landing and Taxi Lights

To Ignition Switch

To Wing Flap System

To Red Doorpost Maplight

To Low-Voltage Warning Light

To Instrument, Radio, Compassand Post Lights

To Oil Temperature Gauge

To Turn Coordinator

To Low-Vacuum Warning Light

Switch/Circuit Breaker toStandby Vacuum Pump

To White Doorpost Light

To Audio Muting Relay

To Control Wheel Maplight

To Navigation Lights

To Dome Light

To Radio

To Radio

To Radio or Transponderand Encoding Altimeter

To Radio

FUELIND.

BCNPITOT

PULLOFF STROBE

RADIOFAN

LDGLTS

FLAP

INSTLTS

STBY VAC

RADIO 1

RADIO 2

RADIO 3

NAVDOME

RADIO 4

Low-VoltageWarning Light

Low Volt Out

Power In

Sense (+)

Field

Sense (-)

GroundG

F

B

Pull Off

ALT

AlternatorControl

Unit

ALT

BAT

+

-

ToWingFlap

CircuitBreaker

RL

Battery

BatteryContactor

Magnetos

Ground ServicePlug Receptacle

StarterContactor

Starter

Flight HourRecorder

Oil PressureSwitch

Clock orDigital Clock

Ammeter

AlternatorField Circuit

Breaker

Master Switch

Alternator

CODE

Circuit Breaker (Auto-Reset) Fuse Diode Resistor

Circuit Breaker (Pull-Off,Push-to-Reset)

To Inst LTS Circuit Breaker

Capacitor (Noise Filter)

Circuit Breaker (Push to Reset)

Figure 5-23. Electrical system schematic.

Figure 5-24. Ammeter and loadmeter.

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generating capacity of the electrical system by the elec-trical accessories and battery. When all electrical com-ponents are turned off, it reflects only the amount ofcharging current demanded by the battery.

A voltage regulator controls the rate of charge to thebattery by stabilizing the generator or alternatorelectrical output. The generator/alternator voltageoutput should be higher than the battery voltage. Forexample, a 12-volt battery would be fed by agenerator/alternator system of approximately 14 volts.The difference in voltage keeps the battery charged.

HYDRAULIC SYSTEMSThere are multiple applications for hydraulic use inairplanes, depending on the complexity of the airplane.For example, hydraulics are often used on smallairplanes to operate wheel brakes, retractable landinggear, and some constant-speed propellers. On largeairplanes, hydraulics are used for flight controlsurfaces, wing flaps, spoilers, and other systems.

A basic hydraulic system consists of a reservoir, pump(either hand, electric, or engine driven), a filter to keepthe fluid clean, selector valve to control the direction offlow, relief valve to relieve excess pressure, and anactuator.

The hydraulic fluid is pumped through the system to anactuator or servo. Servos can be either single-acting ordouble-acting servos based on the needs of the system.This means that the fluid can be applied to one or bothsides of the servo, depending on the servo type, andtherefore provides power in one direction with asingle-acting servo. A servo is a cylinder with a pistoninside that turns fluid power into work and creates thepower needed to move an aircraft system or flightcontrol. The selector valve allows the fluid direction tobe controlled. This is necessary for operations like theextension and retraction of landing gear where the fluidmust work in two different directions. The relief valveprovides an outlet for the system in the event ofexcessive fluid pressure in the system. Each systemincorporates different components to meet theindividual needs of different aircraft.

A mineral-based fluid is the most widely used type forsmall airplanes. This type of hydraulic fluid, which is akerosene-like petroleum product, has good lubricatingproperties, as well as additives to inhibit foaming andprevent the formation of corrosion. It is quite stablechemically, has very little viscosity change withtemperature, and is dyed for identification. Sinceseveral types of hydraulic fluids are commonly used,

make sure your airplane is serviced with the typespecified by the manufacturer. Refer to the AFM, POH,or the Maintenance Manual. [Figure 5-25]

LANDING GEARThe landing gear forms the principal support of theairplane on the surface. The most common type oflanding gear consists of wheels, but airplanes can alsobe equipped with floats for water operations, or skis forlanding on snow. [Figure 5-26]

The landing gear on small airplanes consists of threewheelstwo main wheels, one located on each side ofthe fuselage, and a third wheel, positioned either at thefront or rear of the airplane. Landing gear employing arear-mounted wheel is called a conventional landinggear. Airplanes with conventional landing gear areoften referred to as tailwheel airplanes. When the thirdwheel is located on the nose, it is called a nosewheel,and the design is referred to as a tricycle gear. Asteerable nosewheel or tailwheel permits the airplaneto be controlled throughout all operations while onthe ground.

TRICYCLE LANDING GEAR AIRPLANESA tricycle gear airplane has three main advantages:

Servo—A motor or other form of actuator which receives a small signalfrom the control device and exerts a large force to accomplish thedesired work.

Reservoir Double-Acting

Cylinder

Motion

Selector Valve

C.V. C.V.Pump

Hydraulic Fluid Supply

Hydraulic Pressure Return Fluid

System ReliefValve

Figure 5-25. Basic hydraulic system.

Figure 5-26. The landing gear supports the airplane duringthe takeoff run, landing, taxiing, and when parked.

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1. It allows more forceful application of the brakesduring landings at high speeds without resultingin the airplane nosing over.

2. It permits better forward visibility for the pilotduring takeoff, landing, and taxiing.

3. It tends to prevent ground looping (swerving) byproviding more directional stability duringground operation since the airplane’s center ofgravity (CG) is forward of the main wheels. Theforward CG, therefore, tends to keep the airplanemoving forward in a straight line rather thanground looping.

Nosewheels are either steerable or castering. Steerablenosewheels are linked to the rudders by cables or rods,while castering nosewheels are free to swivel. In bothcases, you steer the airplane using the rudder pedals.However, airplanes with a castering nosewheel mayrequire you to combine the use of the rudder pedalswith independent use of the brakes.

TAILWHEEL LANDING GEAR AIRPLANESOn tailwheel airplanes, two main wheels, which areattached to the airframe ahead of its center of gravity,support most of the weight of the structure, while atailwheel at the very back of the fuselage provides athird point of support. This arrangement allowsadequate ground clearance for a larger propeller and ismore desirable for operations on unimproved fields.[Figure 5-27]

The main drawback with the tailwheel landing gear isthat the center of gravity is behind the main gear. Thismakes directional control more difficult while on theground. If you allow the airplane to swerve whilerolling on the ground at a speed below that at which therudder has sufficient control, the center of gravity willattempt to get ahead of the main gear. This may causethe airplane to ground loop.

Another disadvantage for tailwheel airplanes is the lackof good forward visibility when the tailwheel is on ornear the surface. Because of the associated hazards,specific training is required in tailwheel airplanes.

FIXED AND RETRACTABLE LANDING GEARLanding gear can also be classified as either fixed orretractable. A fixed gear always remains extended andhas the advantage of simplicity combined with lowmaintenance. A retractable gear is designed tostreamline the airplane by allowing the landing gear tobe stowed inside the structure during cruising flight.[Figure 5-28]

BRAKESAirplane brakes are located on the main wheels and areapplied by either a hand control or by foot pedals (toeor heel). Foot pedals operate independently and allowfor differential braking. During ground operations,differential braking can supplement nosewheel/tail-wheel steering.

AUTOPILOTAutopilots are designed to control the aircraft and helpreduce the pilot’s workload. The limitations of theautopilot depend on the complexity of the system. The

Figure 5-27.Tailwheel landing gear.

Figure 5-28. Fixed and retractable gear airplanes.

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common features available on an autopilot are altitudeand heading hold. More advanced systems may includea vertical speed and/or indicated airspeed holdmode. Most autopilot systems are coupled tonavigational aids.

An autopilot system consists of servos that actuate theflight controls. The number and location of theseservos depends on the complexity of the system. Forexample, a single-axis autopilot controls the aircraftabout the longitudinal axis and a servo actuates theailerons. A three-axis autopilot controls the aircraftabout the longitudinal, lateral, and vertical axes; andthree different servos actuate the ailerons, the elevator,and the rudder.

The autopilot system also incorporates a disconnectsafety feature to automatically or manually disengagethe system. Autopilots can also be manuallyoverridden. Because autopilot systems differ widely intheir operation, refer to the autopilot operatinginstructions in the AFM or POH.

PRESSURIZED AIRPLANESWhen an airplane is flown at a high altitude, itconsumes less fuel for a given airspeed than it does forthe same speed at a lower altitude. In other words, theairplane is more efficient at a high altitude. In addition,bad weather and turbulence may be avoided by flyingin the relatively smooth air above the storms. Becauseof the advantages of flying at high altitudes,many modern general aviation-type airplanes arebeing designed to operate in that environment. It isimportant that pilots transitioning to such sophisticatedequipment be familiar with at least the basicoperating principles.

A cabin pressurization system accomplishes severalfunctions in providing adequate passenger comfort andsafety. It maintains a cabin pressure altitude ofapproximately 8,000 feet at the maximum designedcruising altitude of the airplane, and prevents rapidchanges of cabin altitude that may be uncomfortable or

cause injury to passengers and crew. In addition, thepressurization system permits a reasonably fastexchange of air from the inside to the outside of thecabin. This is necessary to eliminate odors and toremove stale air. [Figure 5-29]

Pressurization of the airplane cabin is an acceptedmethod of protecting occupants against the effects ofhypoxia. Within a pressurized cabin, occupants can betransported comfortably and safely for long periods oftime, particularly if the cabin altitude is maintained at8,000 feet or below, where the use of oxygenequipment is not required. The flight crew in this typeof airplane must be aware of the danger of accidentalloss of cabin pressure and must be prepared to deal withsuch an emergency whenever it occurs.

In the typical pressurization system, the cabin, flightcompartment, and baggage compartments areincorporated into a sealed unit that is capable ofcontaining air under a pressure higher than outsideatmospheric pressure. On aircraft powered by turbineengines, bleed air from the engine compressor section isused to pressurize the cabin. Superchargers may be usedon older model turbine powered airplanes to pump airinto the sealed fuselage. Piston-powered airplanes mayuse air supplied from each engine turbocharger througha sonic venturi (flow limiter). Air is released from thefuselage by a device called an outflow valve. Theoutflow valve, by regulating the air exit, provides aconstant inflow of air to the pressurized area.[Figure 5-30]

To understand the operating principles ofpressurization and air-conditioning systems, it isnecessary to become familiar with some of the relatedterms and definitions, such as:

• Aircraft altitude—the actual height above sealevel at which the airplane is flying.

• Ambient temperature—the temperature in thearea immediately surrounding the airplane.

Altitude (ft) Pressure (p.s.i.) Altitude (ft) Pressure (p.s.i.)

Sea Level

2,000

4,000

6,000

8,000

10,000

12,000

14,000

14.7

13.7

12.7

11.8

10.9

10.1

9.4

8.6

16,000

18,000

20,000

22,000

24,000

26,000

28,000

30,000

8.0

7.3

6.8

6.2

5.7

5.2

4.8

4.4

STANDARD ATMOSPHERIC PRESSURE

At an altitude of 28,000 feet, standard atmospheric pressure is 4.8 p.s.i. By adding this pressure to the cabin pressure differential of 6.1 p.s.i.d., a total air pressure of 10.9 p.s.i. is obtained.

The altitude where the standard air pressure is equal to 10.9 p.s.i can be found at 8,000 feet.

Figure 5-29. Standard atmospheric pressure chart.

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• Ambient pressure—the pressure in the areaimmediately surrounding the airplane.

• Cabin altitude—used to express cabin pressurein terms of equivalent altitude above sea level.

• Differential pressure—the difference in pressurebetween the pressure acting on one side of a walland the pressure acting on the other side of thewall. In aircraft air-conditioning and pressurizingsystems, it is the difference between cabinpressure and atmospheric pressure.

The cabin pressure control system provides cabinpressure regulation, pressure relief, vacuum relief, andthe means for selecting the desired cabin altitude in theisobaric and differential range. In addition, dumping ofthe cabin pressure is a function of the pressure controlsystem. A cabin pressure regulator, an outflow valve,and a safety valve are used to accomplish thesefunctions.

The cabin pressure regulator controls cabin pressure toa selected value in the isobaric range and limits cabinpressure to a preset differential value in the differentialrange. When the airplane reaches the altitude at whichthe difference between the pressure inside and outsidethe cabin is equal to the highest differential pressure for

which the fuselage structure is designed, a furtherincrease in airplane altitude will result in acorresponding increase in cabin altitude. Differentialcontrol is used to prevent the maximum differentialpressure, for which the fuselage was designed, frombeing exceeded. This differential pressure isdetermined by the structural strength of the cabin andoften by the relationship of the cabin size to theprobable areas of rupture, such as window areasand doors.

The cabin air pressure safety valve is a combinationpressure relief, vacuum relief, and dump valve. Thepressure relief valve prevents cabin pressure fromexceeding a predetermined differential pressure aboveambient pressure. The vacuum relief prevents ambientpressure from exceeding cabin pressure by allowingexternal air to enter the cabin when ambient pressureexceeds cabin pressure. The cockpit control switchactuates the dump valve. When this switch ispositioned to ram, a solenoid valve opens, causing thevalve to dump cabin air to atmosphere.

The degree of pressurization and the operating altitudeof the aircraft are limited by several critical designfactors. Primarily the fuselage is designed to withstanda particular maximum cabin differential pressure.

Several instruments are used in conjunction with thepressurization controller. The cabin differentialpressure gauge indicates the difference between insideand outside pressure. This gauge should be monitoredto assure that the cabin does not exceed the maximumallowable differential pressure. A cabin altimeter is alsoprovided as a check on the performance of the system.In some cases, these two instruments are combined intoone. A third instrument indicates the cabin rate of climbor descent. A cabin rate-of-climb instrument and acabin altimeter are illustrated in Figure 5-31 onpage 5-26.

Decompression is defined as the inability of theairplane’s pressurization system to maintain its designedpressure differential. This can be caused by amalfunction in the pressurization system or structuraldamage to the airplane. Physiologically, decompressionsfall into two categories; they are:

• Explosive Decompression—Explosive decom-pression is defined as a change in cabin pressurefaster than the lungs can decompress; therefore, itis possible that lung damage may occur. Normally,the time required to release air from the lungswithout restrictions, such as masks, is 0.2 seconds.Most authorities consider any decompression thatoccurs in less than 0.5 seconds as explosive andpotentially dangerous.

Air Scoops

Heat ShroudCabin

Heat Valve

Heat Exchanger

TurbochargerCompressor Section

Flow Control Venturi

Forward Air Outlet

Floor Level Outlets

To CabinAltitudeController

Outflow ValveSafety/Dump Valve

BLUE – Ambient Air

RED – Compressor Discharge Air

ORANGE –Pressurization Air

CODE

BROWN – Pre-heatedAmbient Air

GREEN – ConditionedPressurization Air

Pressurized Cabin

Figure 5-30. High performance airplane pressurizationsystem.

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• Rapid Decompression—Rapid decompression isdefined as a change in cabin pressure where thelungs can decompress faster than the cabin; there-fore, there is no likelihood of lung damage.

During an explosive decompression, there may benoise, and for a split second, one may feel dazed. Thecabin air will fill with fog, dust, or flying debris. Fogoccurs due to the rapid drop in temperature and thechange of relative humidity. Normally, the ears clearautomatically. Air will rush from the mouth and nosedue to the escape of air from the lungs, and may benoticed by some individuals.

The primary danger of decompression is hypoxia.Unless proper utilization of oxygen equipment isaccomplished quickly, unconsciousness may occur in avery short time. The period of useful consciousness isconsiderably shortened when a person is subjected to arapid decompression. This is due to the rapid reductionof pressure on the body—oxygen in the lungs isexhaled rapidly. This in effect reduces the partialpressure of oxygen in the blood and therefore reducesthe pilot’s effective performance time by one-third toone-fourth its normal time. For this reason, the oxygenmask should be worn when flying at very high altitudes(35,000 feet or higher). It is recommended that thecrewmembers select the 100 percent oxygen setting onthe oxygen regulator at high altitude if the airplane isequipped with a demand or pressure demand oxygensystem.

Another hazard is being tossed or blown out of theairplane if near an opening. For this reason, individualsnear openings should wear safety harnesses or seatbeltsat all times when the airplane is pressurized and theyare seated.

Another potential hazard during high altitudedecompressions is the possibility of evolved gasdecompression sicknesses. Exposure to wind blasts andextremely cold temperatures are other hazards onemight have to face.

Rapid descent from altitude is necessary if theseproblems are to be minimized. Automatic visual andaural warning systems are included in the equipment ofall pressurized airplanes.

OXYGEN SYSTEMSMost high altitude airplanes come equipped with sometype of fixed oxygen installation. If the airplane doesnot have a fixed installation, portable oxygenequipment must be readily accessible during flight. Theportable equipment usually consists of a container,regulator, mask outlet, and pressure gauge. Aircraftoxygen is usually stored in high pressure systemcontainers of 1,800 – 2,200 pounds per square inch(p.s.i.). When the ambient temperature surrounding anoxygen cylinder decreases, pressure within thatcylinder will decrease because pressure varies directlywith temperature if the volume of a gas remainsconstant. If a drop in indicated pressure on asupplemental oxygen cylinder is noted, there is noreason to suspect depletion of the oxygen supply, whichhas simply been compacted due to storage of thecontainers in an unheated area of the aircraft. Highpressure oxygen containers should be marked with thep.s.i. tolerance (i.e., 1,800 p.s.i.) before filling thecontainer to that pressure. The containers should besupplied with aviation oxygen only, which is 100percent pure oxygen. Industrial oxygen is not intendedfor breathing and may contain impurities, and medicaloxygen contains water vapor that can freeze in theregulator when exposed to cold temperatures. To assuresafety, oxygen system periodic inspection andservicing should be done.

An oxygen system consists of a mask and a regulatorthat supplies a flow of oxygen dependent upon cabinaltitude. Regulators approved for use up to 40,000 feetare designed to provide zero percent cylinder oxygenand 100 percent cabin air at cabin altitudes of 8,000feet or less, with the ratio changing to 100 percentoxygen and zero percent cabin air at approximately34,000 feet cabin altitude. Regulators approved up to45,000 feet are designed to provide 40 percent cylinderoxygen and 60 percent cabin air at lower altitudes, with

Cabin Pressure Altitude Indicator (Thousands of Feet)

Cabin Differential Pressure Indicator (Pounds Per Square Inch Differential)

Maximum Cabin Differential Pressure Limit

Cabin Rate-Of-ClimbIndicator

Cabin/DifferentialPressure Indicator

Figure 5-31. Cabin pressurization instruments.

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the ratio changing to 100 percent at the higher altitude.Pilots should avoid flying above 10,000 feet withoutoxygen during the day and above 8,000 feet at night.[Figure 5-32]

Pilots should be aware of the danger of fire when usingoxygen. Materials that are nearly fireproof in ordinaryair may be susceptible to burning in oxygen. Oils andgreases may catch fire if exposed to oxygen, andcannot be used for sealing the valves and fittings ofoxygen equipment. Smoking during any kind ofoxygen equipment use is prohibited. Before each flight,the pilot should thoroughly inspect and test all oxygenequipment. The inspection should include a thoroughexamination of the aircraft oxygen equipment,including available supply, an operational check of thesystem, and assurance that the supplemental oxygen isreadily accessible. The inspection should beaccomplished with clean hands and should include avisual inspection of the mask and tubing for tears,cracks, or deterioration; the regulator for valve andlever condition and positions; oxygen quantity; and thelocation and functioning of oxygen pressure gauges,flow indicators and connections. The mask should bedonned and the system should be tested. After anyoxygen use, verify that all components and valves areshut off.

MASKSThere are numerous types of oxygen masks in use thatvary in design detail. It would be impractical to discussall of the types in this handbook. It is important that themasks used be compatible with the particular oxygensystem involved. Crew masks are fitted to the user’sface with a minimum of leakage. Crew masks usuallycontain a microphone. Most masks are the oronasal-type, which covers only the mouth and nose.

Passenger masks may be simple, cup-shaped rubbermoldings sufficiently flexible to obviate individualfitting. They may have a simple elastic head strap or

the passenger may hold them to the face.

All oxygen masks should be kept clean. This reducesthe danger of infection and prolongs the life of themask. To clean the mask, wash it with a mild soap andwater solution and rinse it with clear water. If amicrophone is installed, use a clean swab, instead ofrunning water, to wipe off the soapy solution. The maskshould also be disinfected. A gauze pad that has beensoaked in a water solution of Merthiolate can be usedto swab out the mask. This solution should containone-fifth teaspoon of Merthiolate per quart of water.Wipe the mask with a clean cloth and air dry.

DILUTER DEMAND OXYGEN SYSTEMSDiluter demand oxygen systems supply oxygen onlywhen the user inhales through the mask. An automixlever allows the regulators to automatically mix cabinair and oxygen or supply 100 percent oxygen,depending on the altitude. The demand mask providesa tight seal over the face to prevent dilution withoutside air and can be used safely up to 40,000 feet. Apilot who has a beard or mustache should be sure it istrimmed in a manner that will not interfere with thesealing of the oxygen mask. The fit of the mask aroundthe beard or mustache should be checked on the groundfor proper sealing.

PRESSURE DEMAND OXYGEN SYSTEMSPressure demand oxygen systems are similar to diluterdemand oxygen equipment, except that oxygen issupplied to the mask under pressure at cabin altitudesabove 34,000 feet. Pressure demand regulators alsocreate airtight and oxygen-tight seals, but they alsoprovide a positive pressure application of oxygen to themask face piece that allows the user’s lungs to bepressurized with oxygen. This feature makes pressuredemand regulators safe at altitudes above 40,000 feet.Some systems may have a pressure demand mask withthe regulator attached directly to the mask, rather thanmounted on the instrument panel or other area withinthe flight deck. The mask-mounted regulator eliminatesthe problem of a long hose that must be purged of airbefore 100 percent oxygen begins flowing intothe mask.

CONTINUOUS FLOW OXYGEN SYSTEMContinuous flow oxygen systems are usually providedfor passengers. The passenger mask typically has areservoir bag, which collects oxygen from thecontinuous flow oxygen system during the time whenthe mask user is exhaling. The oxygen collected in thereservoir bag allows a higher aspiratory flow rateduring the inhalation cycle, which reduces the amountof air dilution. Ambient air is added to the supplied

Figure 5-32. Oxygen system regulator.

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oxygen during inhalation after the reservoir bagoxygen supply is depleted. The exhaled air is releasedto the cabin. [Figure 5-33]

SERVICING OF OXYGEN SYSTEMSCertain precautions should be observed wheneveraircraft oxygen systems are to be serviced. Beforeservicing any aircraft with oxygen, consult the specificaircraft service manual to determine the type ofequipment required and procedures to be used. Oxygensystem servicing should be accomplished only whenthe aircraft is located outside of the hangars. Personalcleanliness and good housekeeping are imperativewhen working with oxygen. Oxygen under pressureand petroleum products create spontaneous resultswhen they are brought in contact with each other.Service people should be certain to wash dirt, oil, andgrease (including lip salves and hair oil) from theirhands before working around oxygen equipment. It isalso essential that clothing and tools are free of oil,grease, and dirt. Aircraft with permanently installedoxygen tanks usually require two persons toaccomplish servicing of the system. One should bestationed at the service equipment control valves, andthe other stationed where he or she can observe theaircraft system pressure gauges. Oxygen systemservicing is not recommended during aircraft fuelingoperations or while other work is performed that couldprovide a source of ignition. Oxygen system servicingwhile passengers are on board the aircraft isnot recommended.

ICE CONTROL SYSTEMSIce control systems installed on aircraft consist ofanti-ice and de-ice equipment. Anti-icing equipment isdesigned to prevent the formation of ice, while de-icingequipment is designed to remove ice once it hasformed. Ice control systems protect the leading edge ofwing and tail surfaces, pitot and static port openings,fuel tank vents, stall warning devices, windshields, andpropeller blades. Ice detection lighting may also beinstalled on some airplanes to determine the extent ofstructural icing during night flights. Since manyairplanes are not certified for flight in icing conditions,refer to the AFM or POH for details.

AIRFOIL ICE CONTROLInflatable de-icing boots consist of a rubber sheetbonded to the leading edge of the airfoil. When icebuilds up on the leading edge, an engine-drivenpneumatic pump inflates the rubber boots. Someturboprop aircraft divert engine bleed air to the wing toinflate the rubber boots. Upon inflation, the ice iscracked and should fall off the leading edge of thewing. De-icing boots are controlled from the cockpitby a switch and can be operated in a single cycle orallowed to cycle at automatic, timed intervals. It isimportant that de-icing boots are used in accordancewith the manufacturer’s recommendations. If they areallowed to cycle too often, ice can form over thecontour of the boot and render the boots ineffective.[Figure 5-34]

Many de-icing boot systems use the instrument systemsuction gauge and a pneumatic pressure gauge toindicate proper boot operation. These gauges haverange markings that indicate the operating limits forboot operation. Some systems may also incorporate anannunciator light to indicate proper boot operation.

Proper maintenance and care of de-icing boots isimportant for continued operation of this system. Theyneed to be carefully inspected prior to a flight.

Another type of leading edge protection is the thermalanti-ice system installed on airplanes with turbineengines. This system is designed to prevent the buildupof ice by directing hot air from the compressor sectionof the engine to the leading edge surfaces. The systemis activated prior to entering icing conditions. The hotair heats the leading edge sufficiently to prevent theformation of ice.

Oronasal Mask

Rebreather Bag

Figure 5-33. Continuous flow mask and rebreather bag.

Figure 5-34. De-icing boots on the leading edge of the wing.

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An alternate type of leading edge protection that is notas common as thermal anti-ice and de-icing boots isknown as a weeping wing. The weeping-wing designuses small holes located in the leading edge of thewing. A chemical mixture is pumped to the leadingedge and weeps out through the holes to prevent theformation and buildup of ice.

WINDSCREEN ICE CONTROLThere are two main types of windscreen anti-icesystems. The first system directs a flow of alcohol tothe windscreen. By using it early enough, the alcoholwill prevent ice from building up on the windshield.The rate of alcohol flow can be controlled by a dial inthe cockpit according to procedures recommended bythe airplane manufacturer.

Another effective method of anti-icing equipment isthe electric heating method. Small wires or otherconductive material is imbedded in the windscreen.The heater can be turned on by a switch in the cockpit,at which time electrical current is passed across theshield through the wires to provide sufficient heat toprevent the formation of ice on the windscreen. Theelectrical current can cause compass deviation errors;in some cases, as much as 40°. The heated windscreenshould only be used during flight. Do not leave it onduring ground operations, as it can overheat and causedamage to the windscreen.

PROPELLER ICE CONTROLPropellers are protected from icing by use of alcohol orelectrically heated elements. Some propellers areequipped with a discharge nozzle that is pointed towardthe root of the blade. Alcohol is discharged from thenozzles, and centrifugal force makes the alcohol flowdown the leading edge of the blade. This prevents icefrom forming on the leading edge of the propeller.Propellers can also be fitted with propeller anti-iceboots. The propeller boot is divided into two sections—the inboard and the outboard sections. The boots aregrooved to help direct the flow of alcohol, and they arealso imbedded with electrical wires that carry currentfor heating the propeller. The prop anti-ice system canbe monitored for proper operation by monitoring theprop anti-ice ammeter. During the preflight inspection,check the propeller boots for proper operation. If a bootfails to heat one blade, an unequal blade loading canresult, and may cause severe propeller vibration.[Figure 5-35]

OTHER ICE CONTROL SYSTEMSPitot and static ports, fuel vents, stall-warning sensors,and other optional equipment may be heated by

electrical elements. Operational checks of theelectrically heated systems are to be checked inaccordance with the AFM or POH.

Operation of aircraft anti-icing and de-icing systemsshould be checked prior to encountering icingconditions. Encounters with structural ice requireimmediate remedial action. Anti-icing and de-icingequipment is not intended to sustain long-term flight inicing conditions.

TURBINE ENGINESThe turbine engine produces thrust by increasing thevelocity of the air flowing through the engine. It consistsof an air inlet, compressor, combustion chambers, tur-bine section, and exhaust. [Figure 5-36] The turbine

PROP ANTI-ICE BOOTThe boot is divided into two sections: inboard and outboard. When the anti-ice is operating, the inboard section heats on each blade, and then cycles to the outboard section. If a boot fails to heat properly on one blade, unequal ice loading may result, causing severe vibration.

PROP ANTI-ICE AMMETERWhen the system is operating, the prop ammeter will show in the normal operating range. As each boot section cycles, the ammeter will fluctuate.

Inboard Section

Outboard Section

Figure 5-35. Prop ammeter and anti-ice boots.

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engine has the following advantages over areciprocating engine: less vibration, increased aircraftperformance, reliability, and ease of operation.

TYPES OF TURBINE ENGINESTurbine engines are classified according to the type ofcompressors they use. The compressor types fall intothree categories—centrifugal flow, axial flow, andcentrifugal-axial flow. Compression of inlet air isachieved in a centrifugal flow engine by acceleratingair outward perpendicular to the longitudinal axis ofthe machine. The axial-flow engine compresses air bya series of rotating and stationary airfoils moving theair parallel to the longitudinal axis. The centrifugal-axial flow design uses both kinds of compressors toachieve the desired compression.

The path the air takes through the engine and howpower is produced determines the type of engine. Thereare four types of aircraft turbine engines—turbojet,turboprop, turbofan, and turboshaft.

TURBOJETThe turbojet engine contains four sections: compressor,combustion chamber, turbine section, and exhaust. Thecompressor section passes inlet air at a high rate ofspeed to the combustion chamber. The combustionchamber contains the fuel inlet and igniter forcombustion. The expanding air drives a turbine, whichis connected by a shaft to the compressor, sustainingengine operation. The accelerated exhaust gases fromthe engine provide thrust. This is a basic application ofcompressing air, igniting the fuel-air mixture,producing power to self-sustain the engine operation,and exhaust for propulsion.

Turbojet engines are limited on range and endurance.

They are also slow to respond to throttle applications atslow compressor speeds.

TURBOPROPA turboprop engine is a turbine engine that drives apropeller through a reduction gear. The exhaust gasesdrive a power turbine connected by a shaft that drivesthe reduction gear assembly. Reduction gearing isnecessary in turboprop engines because optimumpropeller performance is achieved at much slowerspeeds than the engine’s operating r.p.m. Turbopropengines are a compromise between turbojet enginesand reciprocating powerplants. Turboprop engines aremost efficient at speeds between 250 and 400 m.p.h.and altitudes between 18,000 and 30,000 feet. Theyalso perform well at the slow airspeeds required fortakeoff and landing, and are fuel efficient. The mini-mum specific fuel consumption of the turboprop engineis normally available in the altitude range of 25,000feet to the tropopause.

TURBOFANTurbofans were developed to combine some of the bestfeatures of the turbojet and the turboprop. Turbofanengines are designed to create additional thrust bydiverting a secondary airflow around the combustionchamber. The turbofan bypass air generates increasedthrust, cools the engine, and aids in exhaust noisesuppression. This provides turbojet-type cruise speedand lower fuel consumption.

The inlet air that passes through a turbofan engine isusually divided into two separate streams of air. Onestream passes through the engine core, while a secondstream bypasses the engine core. It is this bypassstream of air that is responsible for the term “bypassengine.” A turbofan’s bypass ratio refers to the ratio ofthe mass airflow that passes through the fan divided bythe mass airflow that passes through the engine core.

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Figure 5-36. Basic components of a turbine engine.

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TURBOSHAFTThe fourth common type of jet engine is the turboshaft.It delivers power to a shaft that drives something otherthan a propeller. The biggest difference between aturbojet and turboshaft engine is that on a turboshaftengine, most of the energy produced by the expandinggases is used to drive a turbine rather than producethrust. Many helicopters use a turboshaft gas turbineengine. In addition, turboshaft engines are widely usedas auxiliary power units on large aircraft.

PERFORMANCE COMPARISONIt is possible to compare the performance of areciprocating powerplant and different types of turbineengines. However, for the comparison to be accurate,thrust horsepower (usable horsepower) for thereciprocating powerplant must be used rather thanbrake horsepower, and net thrust must be used for theturbine-powered engines. In addition, aircraft designconfiguration, and size must be approximatelythe same.

BHP— Brake horsepower is the horsepower actually delivered to the output shaft. Brake horsepower is the actual usable horsepower.

Net Thrust— The thrust produced by a turbojet orturbofan engine.

THP— Thrust horsepower is the horsepowerequivalent of the thrust produced by a turbojet or turbofan engine.

ESHP— Equivalent shaft horsepower, with respect to turboprop engines, is the sum of the shaft horsepower (SHP) delivered to the propeller and the thrust horsepower (THP) produced bythe exhaust gases.

Figure 5-37 shows how four types of engines comparein net thrust as airspeed is increased. This figure is forexplanatory purposes only and is not for specificmodels of engines. The four types of engines are:

• Reciprocating powerplant.

• Turbine, propeller combination (turboprop).

• Turbine engine incorporating a fan (turbofan).

• Turbojet (pure jet).

The comparison is made by plotting the performancecurve for each engine, which shows how maximumaircraft speed varies with the type of engine used. Sincethe graph is only a means of comparison, numericalvalues for net thrust, aircraft speed, and drag arenot included.

Comparison of the four powerplants on the basis of netthrust makes certain performance capabilities evident.In the speed range shown to the left of Line A, thereciprocating powerplant outperforms the other threetypes. The turboprop outperforms the turbofan in therange to the left of Line C. The turbofan engineoutperforms the turbojet in the range to the left of LineF. The turbofan engine outperforms the reciprocatingpowerplant to the right of Line B and the turboprop tothe right of Line C. The turbojet outperforms thereciprocating powerplant to the right of Line D, theturboprop to the right of Line E, and the turbofan to theright of Line F.

The points where the aircraft drag curve intersects thenet thrust curves are the maximum aircraft speeds. Thevertical lines from each of the points to the baseline ofthe graph indicate that the turbojet aircraft can attain ahigher maximum speed than aircraft equipped with theother types of engines. Aircraft equipped with theturbofan engine will attain a higher maximumspeed than aircraft equipped with a turboprop orreciprocating powerplant.

TURBINE ENGINE INSTRUMENTSEngine instruments that indicate oil pressure, oil temper-ature, engine speed, exhaust gas temperature, and fuelflow are common to both turbine and reciprocatingengines. However, there are some instruments that areunique to turbine engines. These instruments provideindications of engine pressure ratio, turbine dischargepressure, and torque. In addition, most gas turbineengines have multiple temperature-sensing instruments,called thermocouples, that provide pilots withtemperature readings in and around the turbine section.

Aircraft Drag

Airspeed

Net

Thr

ust

ACB

D

E F

TurbojetTurbofan

Turboprop

Reciprocating

Figure 5-37. Engine net thrust versus aircraft speed and drag.

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ENGINE PRESSURE RATIOAn engine pressure ratio (EPR) gauge is used toindicate the power output of a turbojet/turbofan engine.EPR is the ratio of turbine discharge to compressorinlet pressure. Pressure measurements are recorded byprobes installed in the engine inlet and at the exhaust.Once collected, the data is sent to a differentialpressure transducer, which is indicated on a cockpitEPR gauge.

EPR system design automatically compensates for theeffects of airspeed and altitude. However, changes inambient temperature do require a correction to beapplied to EPR indications to provide accurate enginepower settings.

EXHAUST GAS TEMPERATUREA limiting factor in a gas turbine engine is thetemperature of the turbine section. The temperature ofa turbine section must be monitored closely to preventoverheating the turbine blades and other exhaustsection components. One common way of monitoringthe temperature of a turbine section is with an exhaustgas temperature (EGT) gauge. EGT is an engineoperating limit used to monitor overall engineoperating conditions.

Variations of EGT systems bear different names basedon the location of the temperature sensors. Common tur-bine temperature sensing gauges include the turbine inlettemperature (TIT) gauge, turbine outlet temperature(TOT) gauge, interstage turbine temperature (ITT)gauge, and turbine gas temperature (TGT) gauge.

TORQUEMETERTurboprop/turboshaft engine power output is measuredby the torquemeter. Torque is a twisting force appliedto a shaft. The torquemeter measures power applied tothe shaft. Turboprop and turboshaft engines aredesigned to produce torque for driving a propeller.Torquemeters are calibrated in percentage units,foot-pounds, or pounds per square inch.

N1 INDICATORN1 represents the rotational speed of the low pressurecompressor and is presented on the indicator as apercentage of design r.p.m. After start the speed of thelow pressure compressor is governed by the N1 turbinewheel. The N1 turbine wheel is connected to the lowpressure compressor through a concentric shaft.

N2 INDICATORN2 represents the rotational speed of the high pressurecompressor and is presented on the indicator as apercentage of design r.p.m. The high pressurecompressor is governed by the N2 turbine wheel. The

N2 turbine wheel is connected to the high pressurecompressor through a concentric shaft. [Figure 5-38]

TURBINE ENGINE OPERATIONALCONSIDERATIONSBecause of the great variety of turbine engines, it isimpractical to cover specific operational procedures.However, there are certain operational considerationsthat are common to all turbine engines. They are enginetemperature limits, foreign object damage, hot start,compressor stall, and flameout.

ENGINE TEMPERATURE LIMITATIONSThe highest temperature in any turbine engine occursat the turbine inlet. Turbine inlet temperature istherefore usually the limiting factor in turbineengine operation.

THRUST VARIATIONSTurbine engine thrust varies directly with air density.As air density decreases, so does thrust. While bothturbine and reciprocating powered engines are affectedto some degree by high relative humidity, turbineengines will experience a negligible loss of thrust,while reciprocating engines a significant loss of brakehorsepower.

FOREIGN OBJECT DAMAGEDue to the design and function of a turbine engine’s airinlet, the possibility of ingestion of debris alwaysexists. This causes significant damage, particularly tothe compressor and turbine sections. When this occurs,it is called foreign object damage (FOD). Typical FODconsists of small nicks and dents caused by ingestionof small objects from the ramp, taxiway, or runway.However, FOD damage caused by bird strikes or iceingestion can also occur, and may result in totaldestruction of an engine.

Prevention of FOD is a high priority. Some engineinlets have a tendency to form a vortex between theground and the inlet during ground operations. Avortex dissipater may be installed on these engines.Concentric Shaft—One shaft inside another shaft having a common core.

Low PressureCompressor (N1)

High PressureCompressorDrive Shaft

High PressureCompressor (N2)

Low PressureCompressorDrive Shaft

Figure 5-38. Dual-spool axial-flow compressor.

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Other devices, such as screens and/or deflectors, mayalso be utilized. Preflight procedures include a visualinspection for any sign of FOD.

TURBINE ENGINE HOT/HUNG STARTA hot start is when the EGT exceeds the safe limit. Hotstarts are caused by too much fuel entering thecombustion chamber, or insufficient turbine r.p.m. Anytime an engine has a hot start, refer to the AFM, POH,or an appropriate maintenance manual for inspectionrequirements.

If the engine fails to accelerate to the proper speed afterignition or does not accelerate to idle r.p.m., a hungstart has occurred. A hung start, may also be called afalse start. A hung start may be caused by aninsufficient starting power source or fuel controlmalfunction.

COMPRESSOR STALLSCompressor blades are small airfoils and are subject tothe same aerodynamic principles that apply to anyairfoil. A compressor blade has an angle of attack. Theangle of attack is a result of inlet air velocity and thecompressor’s rotational velocity. These two forcescombine to form a vector, which defines the airfoil’sactual angle of attack to the approaching inlet air.

A compressor stall can be described as an imbalancebetween the two vector quantities, inlet velocity andcompressor rotational speed. Compressor stalls occurwhen the compressor blades’ angle of attack exceedsthe critical angle of attack. At this point, smoothairflow is interrupted and turbulence is created withpressure fluctuations. Compressor stalls cause airflowing in the compressor to slow down and stagnate,sometimes reversing direction. [Figure 5-39]

Compressor stalls can be transient andintermittent or steady state and severe. Indications of atransient/intermittent stall are usually an intermittent“bang” as backfire and flow reversal take place. If thestall develops and becomes steady, strong vibration anda loud roar may develop from the continuous flowreversal. Quite often the cockpit gauges will not show amild or transient stall, but will indicate a developedstall. Typical instrument indications includefluctuations in r.p.m., and an increase in exhaust gastemperature. Most transient stalls are not harmful to theengine and often correct themselves after one or twopulsations. The possibility of engine damage, whichmay be severe, from a steady state stall is immediate.Recovery must be accomplished quickly by reducingpower, decreasing the airplane’s angle of attack andincreasing airspeed.

Although all gas turbine engines are subject tocompressor stalls, most models have systems thatinhibit these stalls. One such system uses variable inletguide vane (VIGV) and variable stator vanes, whichdirect the incoming air into the rotor blades at anappropriate angle. The main way to prevent airpressure stalls is to operate the airplane within theparameters established by the manufacturer. If acompressor stall does develop, follow the proceduresrecommended in the AFM or POH.

FLAMEOUTA flameout is a condition in the operation of a gasturbine engine in which the fire in the engineunintentionally goes out. If the rich limit of the fuel/airratio is exceeded in the combustion chamber, the flamewill blow out. This condition is often referred to as arich flameout. It generally results from very fast engineacceleration, where an overly rich mixture causes thefuel temperature to drop below the combustiontemperature. It also may be caused by insufficientairflow to support combustion.

Another, more common flameout occurrence is due tolow fuel pressure and low engine speeds, whichtypically are associated with high-altitude flight. Thissituation also may occur with the engine throttled backduring a descent, which can set up the lean-conditionflameout. A weak mixture can easily cause the flame todie out, even with a normal airflow through the engine.

Any interruption of the fuel supply also can result in aflameout. This may be due to prolonged unusualattitudes, a malfunctioning fuel control system,turbulence, icing or running out of fuel.

Symptoms of a flameout normally are the same asthose following an engine failure. If the flameout is dueto a transitory condition, such as an imbalance betweenfuel flow and engine speed, an airstart may be

Normal InletAirflow

Distorted InletAirflow

Figure 5-39. Comparison of normal and distorted airflow intothe compressor section.

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attempted once the condition is corrected. In any case,pilots must follow the applicable emergencyprocedures outlined in the AFM or POH. Generally,

these procedures contain recommendations concerningaltitude and airspeed where the airstart is most likely tobe successful.

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Flight instruments enable an airplane to be operatedwith maximum performance and enhanced safety,especially when flying long distances. Manufacturersprovide the necessary flight instruments, but to usethem effectively, pilots need to understand how theyoperate. This chapter covers the operational aspects ofthe pitot-static system and associated instruments, thevacuum system and associated instruments, and themagnetic compass.

PITOT-STATIC FLIGHT INSTRUMENTSThere are two major parts of the pitot-static system: theimpact pressure chamber and lines, and the static pressure chamber and lines. They provide the source ofambient air pressure for the operation of the altimeter, vertical speed indicator (vertical velocityindicator), and the airspeed indicator. [Figure 6-1]

IMPACT PRESSURE CHAMBER AND LINESIn this system, the impact air pressure (air striking theairplane because of its forward motion) is taken from apitot tube, which is mounted in locations that provide minimum disturbance or turbulence caused by the motion of the airplane through the air. The staticpressure (pressure of the still air) is usually taken fromthe static line attached to a vent or vents mounted flushwith the side of the fuselage. This compensates for anypossible variation in static pressure due to erraticchanges in airplane attitude.

The openings of both the pitot tube and the static ventmust be checked during the preflight inspection toassure that they are free from obstructions. Blocked or partially blocked openings should be cleaned by a certificated mechanic. Blowing into these openings isnot recommended because this could damage theinstruments.

As the airplane moves through the air, the impact pressure on the open pitot tube affects the pressure inthe pitot chamber. Any change of pressure in the pitotchamber is transmitted through a line connected to theairspeed indicator, which utilizes impact pressure forits operation.

STATIC PRESSURE CHAMBER AND LINESThe static chamber is vented through small holes to the free undisturbed air, and as the atmospheric pressure increases or decreases, the pressure in the static chamber changes accordingly. Again, thispressure change is transmitted through lines to theinstruments which utilize static pressure.

PitotHeater Switch

PitotTube

AirspeedIndicator

VerticalSpeed

Indicator(VSI) Altimeter

DrainOpening

Static Port

ONOFF

Alternate Static Source

ALTSTATIC AIRPULL ON

PressureChamber

Figure 6-1. Pitot-static system and instruments.

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An alternate source for static pressure is provided insome airplanes in the event the static ports becomeblocked. This source usually is vented to the pressureinside the cockpit. Because of the venturi effect of the flow of air over the cockpit, this alternate staticpressure is usually lower than the pressure provided by the normal static air source. When the alternatestatic source is used, the following differences in theinstrument indications usually occur: the altimeter willindicate higher than the actual altitude, the airspeedwill indicate greater than the actual airspeed, and thevertical speed will indicate a climb while in level flight.Consult the Airplane Flight Manual or Pilot’sOperating Handbook (AFM/POH) to determine theamount of error.

If the airplane is not equipped with an alternate staticsource, breaking the glass seal of the vertical speedindicator allows ambient air pressure to enter the staticsystem. This makes the VSI unusable.

ALTIMETERThe altimeter measures the height of the airplane abovea given pressure level. Since it is the only instrumentthat gives altitude information, the altimeter is oneof the most vital instruments in the airplane. To usethe altimeter effectively, its operation and howatmospheric pressure and temperature affect it mustbe thoroughly understood. A stack of sealed aneroidwafers comprises the main component of the altime-ter. These wafers expand and contract with changesin atmospheric pressure from the static source. Themechanical linkage translates these changes intopointer movements on the indicator. [Figure 6-2]

PRINCIPLE OF OPERATIONThe pressure altimeter is an aneroid barometer thatmeasures the pressure of the atmosphere at the levelwhere the altimeter is located, and presents an altitudeindication in feet. The altimeter uses static pressure asits source of operation. Air is denser at sea level thanaloft, so as altitude increases, atmospheric pressuredecreases. This difference in pressure at various levelscauses the altimeter to indicate changes in altitude.

The presentation of altitude varies considerablybetween different types of altimeters. Some have one pointer while others have two or more. Only themultipointer type will be discussed in this handbook.The dial of a typical altimeter is graduated with numer-als arranged clockwise from 0 to 9. Movement of theaneroid element is transmitted through gears to the three hands that indicate altitude. The shortest hand indicates altitude in tens of thousands of feet; theintermediate hand in thousands of feet; and the longesthand in hundreds of feet.

This indicated altitude is correct, however, only whenthe sea level barometric pressure is standard (29.92inches of mercury), the sea level free air temperature isstandard (+15°C or 59°F), and the pressure and temperature decrease at a standard rate with an increasein altitude. Adjustments for nonstandard conditions areaccomplished by setting the corrected pressure into a barometric scale located on the face of the altimeter.Only after the altimeter is set does it indicate the correct altitude.

EFFECT OF NONSTANDARD PRESSURE AND TEMPERATUREIf no means were provided for adjusting altimeters tononstandard pressure, flight could be hazardous. Forexample, if flying from a high-pressure area to a low-pressure area without adjusting the altimeter, theactual altitude of the airplane would be LOWER thanthe indicated altitude. An old saying, “HIGH TO LOW,LOOK OUT BELOW” is a way of remembering whichcondition is dangerous. When flying from a low-pres-sure area to a high-pressure area without adjusting thealtimeter, the actual altitude of the airplane is HIGHERthan the indicated altitude.

Figure 6-3 shows how variations in air temperature alsoaffect the altimeter. On a warm day, a given mass of airexpands to a larger volume than on a cold day, raisingthe pressure levels. For example, the pressure levelwhere the altimeter indicates 5,000 feet is HIGHER ona warm day than under standard conditions. On a coldday, the reverse is true, and the pressure level where thealtimeter indicates 5,000 feet is LOWER.

The adjustment to compensate for nonstandard pres-sure does not compensate for nonstandard temperature.

AneroidWafers

Altimeter Setting Window

AltitudeIndication

Scale10,000 ft Pointer

1,000 ftPointer

100 ft Pointer

Altimeter Setting Adjustment Knob

CrosshatchFlagA crosshatchedarea appearson some altimeterswhen displayingan altitude below10,000 feet MSL.

Static Port

Figure 6-2. Altimeter.

Aneroid—A sealed flexible container, which expands or contracts inrelation to the surrounding air pressure. It is used in an altimeter or abarometer to measure the pressure of the air.

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If terrain or obstacle clearance is a factor in selecting acruising altitude, particularly at higher altitudes,remember to anticipate that a colder-than-standard temperature places the airplane LOWER than thealtimeter indicates. Therefore, it is necessary to use ahigher indicated altitude to provide adequate terrainclearance. Modify the memory aid to “HIGH TO LOWOR HOT TO COLD, LOOK OUT BELOW.”

SETTING THE ALTIMETERMost altimeters are equipped with a barometric pressure setting window (sometimes referred to as theKollsman window) providing a means to adjust thealtimeter. A knob is located at the bottom of the instru-ment for this adjustment.

To adjust the altimeter for variation in atmosphericpressure, the pressure scale in the altimeter setting window, calibrated in inches of mercury (in. Hg) and/ormillibars (Mb), is adjusted to match the given altimetersetting. Altimeter setting is defined as station pressurereduced to sea level. However, an altimeter setting isaccurate only in the vicinity of the reporting station.Therefore, the altimeter must be adjusted as the flightprogresses from one station to the next.

Many pilots confidently expect that the current altimetersetting will compensate for irregularities in atmosphericpressure at all altitudes, but this is not always true. Thealtimeter setting broadcast by ground stations is the

station pressure corrected to mean sea level. It does notaccount for the irregularities at higher levels, particu-larly the effect of nonstandard temperature. However, ifeach pilot in a given area is using the same altimeter setting, each altimeter should be equally affected by temperature and pressure variation errors, making it possible to maintain the desired vertical separationbetween aircraft.

When flying over high, mountainous terrain, certainatmospheric conditions can cause the altimeter to indicate an altitude of 1,000 feet, or more, HIGHERthan the actual altitude. For this reason, a generousmargin of altitude should be allowed—not only for possible altimeter error, but also for possible downdrafts that might be associated with high winds.

To illustrate the use of the altimeter setting system, follow a flight from Dallas Love Field, Texas toAbilene Municipal Airport, Texas via Mineral Wells.Before taking off from Love Field, the pilot receives acurrent altimeter setting of 29.85 from the controltower or automatic terminal information service(ATIS), and sets this value in the altimeter setting

5,000-foot pressure level

4,000-foot pressure level

3,000-foot pressure level

2,000-foot pressure level

1,000-foot pressure level

Sea level

30°C 15°C 0°C

True Altitude

True Altitude

True Altitude

Figure 6-3. Effects of nonstandard temperature on an altimeter.

Automatic Terminal Information Service (ATIS)—The continuousbroadcast of recorded noncontrol information in selected terminalareas. Its purpose is to improve controller effectiveness and to relievefrequency congestion by automating the repetitive transmission ofessential but routine information.

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window. The altimeter indication should then be compared with the known airport elevation of 487 feet.Since most altimeters are not perfectly calibrated, anerror may exist.

When over Mineral Wells, assume the pilot receives acurrent altimeter setting of 29.94 and sets this in thealtimeter window. Before entering the traffic pattern atAbilene Municipal Airport, a new altimeter setting of29.69 is received from the Abilene Control Tower, andset in the altimeter setting window. If the pilot desiresto fly the traffic pattern at approximately 800 feetabove the terrain, and the field elevation of Abilene is1,791 feet, an indicated altitude of 2,600 feet should bemaintained (1,791 feet + 800 feet = 2,591 feet roundedto 2,600 feet).

The importance of properly setting the altimeter cannotbe overemphasized. Assume that the pilot did notadjust the altimeter at Abilene to the current setting,and continued using the Mineral Wells setting of 29.94.When entering the Abilene traffic pattern at an indicated altitude of 2,600 feet, the airplane would beapproximately 250 feet below the proper traffic patternaltitude. Upon landing, the altimeter would indicateapproximately 250 feet higher than the field elevation.

Altimeter setting 29.94Current altimeter setting 29.69Difference .25

(Since 1 inch of pressure is equal to approximately1,000 feet of altitude, .25 � 1,000 feet = 250 feet.)

When determining whether to add or subtract theamount of altimeter error, remember that, when theactual pressure is lower than what is set in the altimeterwindow, the actual altitude of the airplane will be lowerthan what is indicated on the altimeter.

ALTIMETER OPERATIONThere are two means by which the altimeter pointerscan be moved. The first is a change in air pressure,while the other is an adjustment to the barometric scale. When the airplane climbs or descends, changingpressure within the altimeter case expands or contractsthe aneroid barometer. This movement is transmittedthrough mechanical linkage to rotate the pointers. Adecrease in pressure causes the altimeter to indicate anincrease in altitude, and an increase in pressure causesthe altimeter to indicate a decrease in altitude.Accordingly, if the airplane is flown from a pressurelevel of 28.75 in. Hg. to a pressure level of 29.75 in. Hg., the altimeter would show a decrease of approximately 1,000 feet in altitude.

The other method of moving the pointers does notrely on changing air pressure, but the mechanicalconstruction of the altimeter. Do not be confused bythe fact that as the barometric pressure scale ismoved, the indicator needles move in the samedirection, which is opposite to the reaction thepointers have when air pressure changes. To illus-trate this point, suppose the pilot lands at an airportwith an elevation of 1,000 feet and the altimeter iscorrectly set to the current sea level pressure of30.00 in. Hg. While the airplane is parked on theramp, the pressure decreases to 29.50. The altimetersenses this as a climb and now indicates 1,500 feet.When returning to the airplane, if the setting in thealtimeter window is decreased to the current sealevel pressure of 29.50, the indication will bereduced back down to 1,000 feet.

Knowing the airplane’s altitude is vitally importantto a pilot. The pilot must be sure that the airplane isflying high enough to clear the highest terrain orobstruction along the intended route. It is especiallyimportant to have accurate altitude information whenvisibility is restricted. To clear obstructions, the pilotmust constantly be aware of the altitude of the air-plane and the elevation of the surrounding terrain. Toreduce the possibility of a midair collision, it isessential to maintain altitude in accordance with airtraffic rules.

TYPES OF ALTITUDE Altitude is vertical distance above some point or levelused as a reference. There are as many kinds of altitudeas there are reference levels from which altitude ismeasured, and each may be used for specific reasons.Pilots are mainly concerned with five types of altitudes:

Indicated Altitude—That altitude read directly fromthe altimeter (uncorrected) when it is set to the currentaltimeter setting.

True Altitude—The vertical distance of the airplaneabove sea level—the actual altitude. It is oftenexpressed as feet above mean sea level (MSL). Airport,terrain, and obstacle elevations on aeronautical chartsare true altitudes.

Absolute Altitude—The vertical distance of an air-plane above the terrain, or above ground level (AGL).

Pressure Altitude—The altitude indicated when thealtimeter setting window (barometric scale) is adjustedto 29.92. This is the altitude above the standard datumplane, which is a theoretical plane where air pressure

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(corrected to 15°C) equals 29.92 in. Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.

Density Altitude—This altitude is pressure altitudecorrected for variations from standard temperature.When conditions are standard, pressure altitude anddensity altitude are the same. If the temperature isabove standard, the density altitude is higher than pressure altitude. If the temperature is below standard,the density altitude is lower than pressure altitude. Thisis an important altitude because it is directly related tothe airplane’s performance.

As an example, consider an airport with a field elevation of 5,048 feet MSL where the standard temperature is 5°C. Under these conditions, pressurealtitude and density altitude are the same—5,048 feet.If the temperature changes to 30°C, the density altitude increases to 7,855 feet. This means an airplanewould perform on takeoff as though the field elevationwere 7,855 feet at standard temperature. Conversely, atemperature of -25°C would result in a density altitudeof 1,232 feet. An airplane would have much better performance under these conditions.

Instrument Check—To determine the condition of an altimeter, set the barometric scale to the altimetersetting transmitted by the local automated flight service station (AFSS) or any other reliable source. Thealtimeter pointers should indicate the surveyed eleva-tion of the airport. If the indication is off more than 75feet from the surveyed elevation, the instrumentshould be referred to a certificated instrument repairstation for recalibration.

VERTICAL SPEED INDICATORThe vertical speed indicator (VSI), which is sometimescalled a vertical velocity indicator (VVI), indicateswhether the airplane is climbing, descending, or in levelflight. The rate of climb or descent is indicated in feetper minute. If properly calibrated, the VSI indicates zeroin level flight. [Figure 6-4]

PRINCIPLE OF OPERATIONAlthough the vertical speed indicator operates solelyfrom static pressure, it is a differential pressure instrument. It contains a diaphragm with connectinglinkage and gearing to the indicator pointer inside anairtight case. The inside of the diaphragm is connecteddirectly to the static line of the pitot-static system. The area outside the diaphragm, which is inside theinstrument case, is also connected to the static line, butthrough a restricted orifice (calibrated leak).

Both the diaphragm and the case receive air from thestatic line at existing atmospheric pressure. When theairplane is on the ground or in level flight, the pressuresinside the diaphragm and the instrument case remainthe same and the pointer is at the zero indication. Whenthe airplane climbs or descends, the pressure inside the diaphragm changes immediately, but due to themetering action of the restricted passage, the case pressure remains higher or lower for a short time, causing the diaphragm to contract or expand. Thiscauses a pressure differential that is indicated on theinstrument needle as a climb or descent. When the pressure differential stabilizes at a definite ratio, theneedle indicates the rate of altitude change.

The vertical speed indicator is capable of displayingtwo different types of information:

• Trend information shows an immediate indica-tion of an increase or decrease in the airplane’srate of climb or descent.

• Rate information shows a stabilized rate ofchange in altitude.

For example, if maintaining a steady 500-foot perminute (f.p.m.) climb, and the nose is loweredslightly, the VSI immediately senses this change andindicates a decrease in the rate of climb. This firstindication is called the trend. After a short time, theVSI needle stabilizes on the new rate of climb, whichin this example, is something less than 500 f.p.m. Thetime from the initial change in the rate of climb, untilthe VSI displays an accurate indication of the newrate, is called the lag. Rough control technique andturbulence can extend the lag period and cause erraticand unstable rate indications. Some airplanes are

Diaphragm

Direct StaticPressure

CalibratedLeak

Figure 6-4. Vertical speed indicator.

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equipped with an instantaneous vertical speed indicator(IVSI), which incorporates accelerometers to compen-sate for the lag in the typical VSI. [Figure 6-5]

Instrument Check—To verify proper operation, makesure the VSI is indicating near zero prior to takeoff.After takeoff, it should indicate a positive rate of climb.

AIRSPEED INDICATORThe airspeed indicator is a sensitive, differential pres-sure gauge which measures and shows promptly thedifference between pitot or impact pressure, and staticpressure, the undisturbed atmospheric pressure at levelflight. These two pressures will be equal when the airplane is parked on the ground in calm air. When the airplane moves through the air, the pressure on thepitot line becomes greater than the pressure in the staticlines. This difference in pressure is registered by theairspeed pointer on the face of the instrument,which is calibrated in miles per hour, knots, or both.[Figure 6-6]

Pilots should understand the following speeds:

Indicated Airspeed (IAS)—The direct instrumentreading obtained from the airspeed indicator, uncorrected for variations in atmospheric density,installation error, or instrument error. Manufacturersuse this airspeed as the basis for determining airplaneperformance. Takeoff, landing, and stall speeds listedin the AFM or POH are indicated airspeeds and do notnormally vary with altitude or temperature.

Calibrated Airspeed (CAS)—Indicated airspeed corrected for installation error and instrument error.Although manufacturers attempt to keep airspeederrors to a minimum, it is not possible to eliminate all errors throughout the airspeed operating range. Atcertain airspeeds and with certain flap settings, theinstallation and instrument errors may total severalknots. This error is generally greatest at low airspeeds.In the cruising and higher airspeed ranges, indicatedairspeed and calibrated airspeed are approximately thesame. Refer to the airspeed calibration chart to correctfor possible airspeed errors.

True Airspeed (TAS)—Calibrated airspeed correctedfor altitude and nonstandard temperature. Because airdensity decreases with an increase in altitude, an airplane has to be flown faster at higher altitudes tocause the same pressure difference between pitotimpact pressure and static pressure. Therefore, for agiven calibrated airspeed, true airspeed increases asaltitude increases; or for a given true airspeed, calibrated airspeed decreases as altitude increases.

A pilot can find true airspeed by two methods. Themost accurate method is to use a flight computer. Withthis method, the calibrated airspeed is corrected for temperature and pressure variation by using the airspeed correction scale on the computer. Extremelyaccurate electronic flight computers are also available.Just enter the CAS, pressure altitude, and temperatureand the computer calculates the true airspeed.

A second method, which is a “rule of thumb,” will provide the approximate true airspeed. Simply add 2 percent to the calibrated airspeed for each 1,000 feet ofaltitude.

Groundspeed (GS)—The actual speed of the airplaneover the ground. It is true airspeed adjusted for wind.Groundspeed decreases with a headwind, and increaseswith a tailwind.

AIRSPEED INDICATOR MARKINGSAirplanes weighing 12,500 pounds or less, manufac-tured after 1945, and certificated by the FAA, are required to have airspeed indicators marked inaccordance with a standard color-coded marking Knots—Nautical miles per hour.

Diaphragm

Static Air Line

Ram AirPitot Tube

Figure 6-6. Airspeed indicator.

Accelerometer

Inlet FromStatic Port

Calibrated Leak

Figure 6-5. An instantaneous vertical speed indicator incor-porates accelerometers to help the instrument immediatelyindicate changes in vertical speed.

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system. This system of color-coded markings enablesa pilot to determine at a glance certain airspeed limi-tations that are important to the safe operation of theairplane. For example, if during the execution of amaneuver, it is noted that the airspeed needle is in theyellow arc and rapidly approaching the red line, theimmediate reaction should be to reduce airspeed.

As shown in figure 6-7, airspeed indicators on single-engine small airplanes include the following standardcolor-coded markings:

• White arc—This arc is commonly referred to as the flap operating range since its lower limitrepresents the full flap stall speed and its upperlimit provides the maximum flap speed.Approaches and landings are usually flown atspeeds within the white arc.

• Lower limit of white arc (VS0)—The stallingspeed or the minimum steady flight speed in thelanding configuration. In small airplanes, this isthe power-off stall speed at the maximum landingweight in the landing configuration (gear andflaps down).

• Upper limit of the white arc (VFE)—The maxi-mum speed with the flaps extended.

• Green arc—This is the normal operating range ofthe airplane. Most flying occurs within this range.

• Lower limit of green arc (VS1)—The stallingspeed or the minimum steady flight speedobtained in a specified configuration. For mostairplanes, this is the power-off stall speed at themaximum takeoff weight in the clean configuration(gear up, if retractable, and flaps up).

• Upper limit of green arc (VNO)—The maximumstructural cruising speed. Do not exceed thisspeed except in smooth air.

• Yellow arc—Caution range. Fly within this rangeonly in smooth air, and then, only with caution.

• Red line (VNE)—Never-exceed speed. Operatingabove this speed is prohibited since it may resultin damage or structural failure.

OTHER AIRSPEED LIMITATIONSSome important airspeed limitations are not marked on theface of the airspeed indicator, but are found on placardsand in the AFM or POH. These airspeeds include:

• Design maneuvering speed (VA)—This is the“rough air” speed and the maximum speed for abruptmaneuvers. If during flight, rough air or severe turbulence is encountered, reduce the airspeed tomaneuvering speed or less to minimize stress on theairplane structure. It is important to consider weightwhen referencing this speed. For example, VA maybe 100 knots when an airplane is heavily loaded, butonly 90 knots when the load is light.

• Landing gear operating speed (VLO)—The maximum speed for extending or retracting thelanding gear if using an airplane equipped withretractable landing gear.

• Landing gear extended speed (VLE)—The maximum speed at which an airplane can besafely flown with the landing gear extended.

• Best angle-of-climb speed (VX)—The airspeed atwhich an airplane gains the greatest amount ofaltitude in a given distance. It is used during ashort-field takeoff to clear an obstacle.

• Best rate-of-climb speed (VY)—This airspeedprovides the most altitude gain in a given periodof time.

• Minimum control speed (VMC)—This is the min-imum flight speed at which a light, twin-engineairplane can be satisfactorily controlled when anengine suddenly becomes inoperative and theremaining engine is at takeoff power.

• Best rate of climb with one engine inoperative(VYSE)—This airspeed provides the most altitudegain in a given period of time in a light, twin-engine airplane following an engine failure.

Instrument Check—Prior to takeoff, the airspeedindicator should read zero. However, if there is a strongwind blowing directly into the pitot tube, the airspeed

VNE (Red Line)

Yellow Arc

VNO

Green ArcVFE

White Arc

VS1

VSO

Figure 6-7. In addition to delineating various speed ranges,the boundaries of the color-coded arcs also identify airspeedlimitations.

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indicator may read higher than zero. When beginningthe takeoff, make sure the airspeed is increasing at anappropriate rate.

BLOCKAGE OF THE PITOT-STATIC SYSTEMErrors almost always indicate blockage of the pitot tube,the static port(s), or both. Blockage may be caused bymoisture (including ice), dirt, or even insects. During pre-flight, make sure the pitot tube cover is removed. Then,check the pitot and static port openings. A blocked pitottube affects the accuracy of only the airspeed indicator.However, a blockage of the static system not only affectsthe airspeed indicator, but can also cause errors in thealtimeter and vertical speed indicator.

BLOCKED PITOT SYSTEM The pitot system can become blocked completely oronly partially if the pitot tube drain hole remains open.If the pitot tube becomes blocked and its associateddrain hole remains clear, ram air no longer is able toenter the pitot system. Air already in the system willvent through the drain hole, and the remaining pressurewill drop to ambient (outside) air pressure. Under thesecircumstances, the airspeed indicator reading decreasesto zero, because the airspeed indicator senses no difference between ram and static air pressure. The airspeed indicator acts as if the airplane were stationaryon the ramp. The apparent loss of airspeed is not usually instantaneous. Instead, the airspeed will droptoward zero. [Figure 6-8]

If the pitot tube, drain hole, and static system allbecome blocked in flight, changes in airspeed will notbe indicated, due to the trapped pressures. However, ifthe static system remains clear, the airspeed indicatoracts as an altimeter. An apparent increase in the ram airpressure relative to static pressure occurs as altitudeincreases above the level where the pitot tube and drainhole became blocked. This pressure differential causes

the airspeed indicator to show an increase in speed. Adecrease in indicated airspeed occurs as the airplanedescends below the altitude at which the pitot systembecame blocked. [Figure 6-9]

The pitot tube may become blocked during flightthrough visible moisture. Some airplanes may beequipped with pitot heat for flight in visible moisture.Consult the AFM or POH for specific proceduresregarding the use of pitot heat.

BLOCKED STATIC SYSTEMIf the static system becomes blocked but the pitot tuberemains clear, the airspeed indicator continues to operate; however, it is inaccurate. Airspeed indicationsare slower than the actual speed when the airplane isoperated above the altitude where the static portsbecame blocked, because the trapped static pressure ishigher than normal for that altitude. When operating at

6-8

Static Port

Pitot Tube

Blockage

Drain Hole

Climb

Descent

Figure 6-9. Blocked pitot system with clear static system.

Static Port

Pitot Tube

Blockage

Drain Hole

Figure 6-8. A blocked pitot tube, but clear drain hole.

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a lower altitude, a faster than actual airspeed is displayed due to the relatively low static pressuretrapped in the system.

A blockage of the static system also affects the altimeterand VSI. Trapped static pressure causes the altimeter tofreeze at the altitude where the blockage occurred. Inthe case of the VSI, a blocked static system produces acontinuous zero indication. [Figure 6-10]

GYROSCOPIC FLIGHT INSTRUMENTSSeveral flight instruments utilize the properties of a gyroscope for their operation. The most commoninstruments containing gyroscopes are the turn coordinator, heading indicator, and the attitude indicator. To understand how these instruments operaterequires knowledge of the instrument power systems,gyroscopic principles, and the operating principles ofeach instrument.

GYROSCOPIC PRINCIPLESAny spinning object exhibits gyroscopic properties. Awheel or rotor designed and mounted to utilize theseproperties is called a gyroscope. Two important designcharacteristics of an instrument gyro are great weightfor its size, or high density, and rotation at high speedwith low friction bearings.

There are two general types of mountings; the type useddepends upon which property of the gyro is utilized. Afreely or universally mounted gyroscope is free to rotatein any direction about its center of gravity. Such a wheelis said to have three planes of freedom. The wheel orrotor is free to rotate in any plane in relation to the baseand is so balanced that with the gyro wheel at rest, it willremain in the position in which it is placed. Restricted or

semirigidly mounted gyroscopes are those mounted sothat one of the planes of freedom is held fixed in relationto the base.

There are two fundamental properties of gyroscopicaction—rigidity in space and precession.

RIGIDITY IN SPACERigidity in space refers to the principle that a gyro-scope remains in a fixed position in the plane in whichit is spinning. By mounting this wheel, or gyroscope,on a set of gimbal rings, the gyro is able to rotate freelyin any direction. Thus, if the gimbal rings are tilted,twisted, or otherwise moved, the gyro remains in theplane in which it was originally spinning. [Figure 6-11]

PRECESSIONPrecession is the tilting or turning of a gyro in responseto a deflective force. The reaction to this force does notoccur at the point where it was applied; rather, it occursat a point that is 90° later in the direction of rotation.This principle allows the gyro to determine a rate ofturn by sensing the amount of pressure created by a change in direction. The rate at which the gyro precesses is inversely proportional to the speed of therotor and proportional to the deflective force.

Pitot Tube

InaccurateAirspeedIndications

Constant ZeroIndication on VSI

FrozenAltimeter

StaticPort

Blockage

Figure 6-10. Blocked static system.

Figure 6-11. Regardless of the position of its base, a gyrotends to remain rigid in space, with its axis of rotationpointed in a constant direction.

Gimbal Ring—A type of support that allows an object, such as a gyro-scope, to remain in an upright condition when its base is tilted.

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Precession can also create some minor errors in someinstruments. [Figure 6-12]

SOURCES OF POWERIn some airplanes, all the gyros are vacuum, pressure,or electrically operated; in others, vacuum or pressuresystems provide the power for the heading and attitudeindicators, while the electrical system provides thepower for the turn coordinator. Most airplanes have atleast two sources of power to ensure at least one sourceof bank information if one power source fails.

The vacuum or pressure system spins the gyro by drawing a stream of air against the rotor vanes to spinthe rotor at high speed, much like the operation of awaterwheel or turbine. The amount of vacuum or

pressure required for instrument operation varies, but isusually between 4.5 and 5.5 in. Hg.

One source of vacuum for the gyros is a vane-typeengine-driven pump that is mounted on the accessorycase of the engine. Pump capacity varies in differentairplanes, depending on the number of gyros.

A typical vacuum system consists of an engine-drivenvacuum pump, relief valve, air filter, gauge, and tubingnecessary to complete the connections. The gauge ismounted in the airplane’s instrument panel and indi-cates the amount of pressure in the system (vacuum is measured in inches of mercury less than ambient pressure).

As shown in figure 6-13, air is drawn into the vacuumsystem by the engine-driven vacuum pump. It first goesthrough a filter, which prevents foreign matter fromentering the vacuum or pressure system. The air thenmoves through the attitude and heading indicators,where it causes the gyros to spin. A relief valve prevents the vacuum pressure, or suction, from exceed-ing prescribed limits. After that, the air is expelledoverboard or used in other systems, such as for inflating pneumatic deicing boots.

It is important to monitor vacuum pressure duringflight, because the attitude and heading indicators maynot provide reliable information when suction pressureis low. The vacuum, or suction, gauge generally ismarked to indicate the normal range. Some airplanesare equipped with a warning light that illuminates whenthe vacuum pressure drops below the acceptable level.

TURN INDICATORSAirplanes use two types of turn indicators—the turn-and-slip indicator and the turn coordinator. Because of

Heading Indicator

Vacuum Relief Valve

VacuumPump

AttitudeIndicator

SuctionGauge

Vacuum Air Filter

OverboardVent Line

Figure 6-13.Typical Vacuum System.

Plane of Rotation Plane of Force

Plane ofPrecession

FORCE

Figure 6-12. Precession of a gyroscope resulting from anapplied deflective force.

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the way the gyro is mounted, the turn-and-slip indica-tor only shows the rate of turn in degrees per second.Because the gyro on the turn coordinator is set at anangle, or canted, it can initially also show roll rate.Once the roll stabilizes, it indicates rate of turn. Both instruments indicate turn direction and quality(coordination), and also serve as a backup source of bank information in the event an attitude indicator fails. Coordination is achieved by referring tothe inclinometer, which consists of a liquid-filledcurved tube with a ball inside. [Figure 6-14]

TURN-AND-SLIP INDICATORThe gyro in the turn-and-slip indicator rotates in the vertical plane, corresponding to the airplane’s longitudinal axis. A single gimbal limits the planes inwhich the gyro can tilt, and a spring tries to return it tocenter. Because of precession, a yawing force causesthe gyro to tilt left or right as viewed from the pilot seat.The turn-and-slip indicator uses a pointer, called theturn needle, to show the direction and rate of turn.

TURN COORDINATORThe gimbal in the turn coordinator is canted; therefore,its gyro can sense both rate of roll and rate of turn.Since turn coordinators are more prevalent in training

airplanes, this discussion concentrates on that instru-ment. When rolling into or out of a turn, the miniatureairplane banks in the direction the airplane is rolled. Arapid roll rate causes the miniature airplane to bankmore steeply than a slow roll rate.

The turn coordinator can be used to establish and maintain a standard-rate-turn by aligning the wing ofthe miniature airplane with the turn index. The turncoordinator indicates only the rate and direction ofturn; it does not display a specific angle of bank.

INCLINOMETERThe inclinometer is used to depict airplane yaw, whichis the side-to-side movement of the airplane’s nose.During coordinated, straight-and-level flight, the forceof gravity causes the ball to rest in the lowest part of thetube, centered between the reference lines. Coordinatedflight is maintained by keeping the ball centered. If theball is not centered, it can be centered by using the rud-der. To do this, apply rudder pressure on the side wherethe ball is deflected. Use the simple rule, “step on theball,” to remember which rudder pedal to press.

If aileron and rudder are coordinated during a turn, theball remains centered in the tube. If aerodynamic forcesare unbalanced, the ball moves away from the center ofthe tube. As shown in figure 6-15, in a slip, the rate of

GyroRotation

GimbalRotation

TURN-AND-SLIPINDICATOR

Gimbal

GimbalRotation

GyroRotation

Canted Gyro

TURNCOORDINATOR

HorizontalGyro

Standard RateTurn Index

Standard RateTurn Index

Inclinometer

Figure 6-14. Turn indicators rely on controlled precession fortheir operation.

Slipping Turn Skidding Turn

Coordinated Turn

Standard-Rate-Turn—A turn of 3° per second. A complete 360° turntakes 2 minutes. A rule of thumb for determining the approximate bankangle required for a standard-rate turn is to divide the true airspeed by10 and add one-half the result. For example, at 120 knots, approximately18° of bank is required (120 � 10 = 12 + 6 = 18). At 200 knots, it wouldtake approximately 30° of bank for a standard-rate-turn.

Inclinometer—An instrument consisting of a curved glass tube, housinga glass ball, and damped with a fluid similar to kerosene. It may be usedto indicate inclination, as a level, or, as used in the turn indicators, toshow the relationship between gravity and centrifugal force in a turn.

Figure 6-15. If inadequate right rudder is applied in a rightturn, a slip results.Too much right rudder causes the airplaneto skid through the turn. Centering the ball results in a coordinated turn.

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turn is too slow for the angle of bank, and the ballmoves to the inside of the turn. In a skid, the rate ofturn is too great for the angle of bank, and the ballmoves to the outside of the turn. To correct for theseconditions, and improve the quality of the turn, remem-ber to “step on the ball.” Varying the angle of bank canalso help restore coordinated flight from a slip or skid.To correct for a slip, decrease bank and/or increase therate of turn. To correct for a skid, increase the bankand/or decrease the rate of turn.

Instrument Check—During the preflight, check tosee that the inclinometer is full of fluid and has no airbubbles. The ball should also be resting at its lowestpoint. When taxiing, the turn coordinator should indi-cate a turn in the correct direction.

THE ATTITUDE INDICATORThe attitude indicator, with its miniature airplane andhorizon bar, displays a picture of the attitude of the air-plane. The relationship of the miniature airplane to thehorizon bar is the same as the relationship of the realairplane to the actual horizon. The instrument gives aninstantaneous indication of even the smallest changesin attitude.

The gyro in the attitude indicator is mounted on a hori-zontal plane and depends upon rigidity in space for itsoperation. The horizon bar represents the true horizon.This bar is fixed to the gyro and remains in a horizontalplane as the airplane is pitched or banked about its lateral or longitudinal axis, indicating the attitude ofthe airplane relative to the true horizon. [Figure 6-16]

An adjustment knob is provided with which the pilotmay move the miniature airplane up or down to alignthe miniature airplane with the horizon bar to suit thepilot’s line of vision. Normally, the miniature airplane

is adjusted so that the wings overlap the horizon barwhen the airplane is in straight-and-level cruisingflight.

The pitch and bank limits depend upon the make andmodel of the instrument. Limits in the banking planeare usually from 100° to 110°, and the pitch limits areusually from 60° to 70°. If either limit is exceeded, theinstrument will tumble or spill and will give incorrectindications until restabilized. A number of modern attitude indicators will not tumble.

Every pilot should be able to interpret the banking scaleillustrated in figure 6-17. Most banking scale indicatorson the top of the instrument move in the same directionfrom that in which the airplane is actually banked.Some other models move in the opposite direction fromthat in which the airplane is actually banked. This mayconfuse the pilot if the indicator is used to determinethe direction of bank. This scale should be used only tocontrol the degree of desired bank. The relationship ofthe miniature airplane to the horizon bar should be usedfor an indication of the direction of bank.

The attitude indicator is reliable and the most realisticflight instrument on the instrument panel. Its indica-tions are very close approximations of the actual attitude of the airplane.

HEADING INDICATORThe heading indicator (or directional gyro) is funda-mentally a mechanical instrument designed to facilitatethe use of the magnetic compass. Errors in the magnetic compass are numerous, making straight flightand precision turns to headings difficult to accomplish,particularly in turbulent air. A heading indicator, however, is not affected by the forces that make themagnetic compass difficult to interpret. [Figure 6-18]

Bank Index

Gyro

GimbalRotation

RollGimbal

PitchGimbal

HorizonReference

Arm

Figure 6-16. Attitude indicator. Adjustment Gears AdjustmentKnob

GimbalRotation

Gimbal Gyro

MainDrive Gear

CompassCard Gear

Figure 6-18. A heading indicator displays headings based ona 360° azimuth, with the final zero omitted. For example, a 6represents 060°, while a 21 indicates 210°. The adjustmentknob is used to align the heading indicator with the magneticcompass.

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Pointer

10°20°

30°

60°

Bank Scale

Miniature Airplane

Artificial Horizon

LevelLeft Bank

ClimbingLeft Bank

LevelClimb

ClimbingRight Bank

LevelRight Bank

DescendingLeft Bank

LevelDescent

DescendingRight Bank

Adjustment Knob

Figure 6-17. Attitude representation by the attitude indicator corresponds to that of the airplane to the real horizon.

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The operation of the heading indicator depends uponthe principle of rigidity in space. The rotor turns in avertical plane, and fixed to the rotor is a compass card.Since the rotor remains rigid in space, the points on thecard hold the same position in space relative to the ver-tical plane. As the instrument case and the airplanerevolve around the vertical axis, the card provides clearand accurate heading information.

Because of precession, caused by friction, the headingindicator will creep or drift from a heading to which itis set. Among other factors, the amount of drift dependslargely upon the condition of the instrument. If thebearings are worn, dirty, or improperly lubricated, thedrift may be excessive. Another error in the headingindicator is caused by the fact that the gyro is orientedin space, and the earth rotates in space at a rate of 15°in 1 hour. Thus, discounting precession caused by fric-tion, the heading indicator may indicate as much as 15°error per every hour of operation.

Some heading indicators receive a magnetic north refer-ence from a magnetic slaving transmitter, and generallyneed no adjustment. Heading indicators that do not havethis automatic north-seeking capability are called “free”gyros, and require periodic adjustment. It is importantto check the indications frequently (approximatelyevery 15 minutes) and reset the heading indicator toalign it with the magnetic compass when required.Adjust the heading indicator to the magnetic compassheading when the airplane is straight and level at a con-stant speed to avoid compass errors.

The bank and pitch limits of the heading indicator varywith the particular design and make of instrument. Onsome heading indicators found in light airplanes, thelimits are approximately 55° of pitch and 55° of bank.When either of these attitude limits is exceeded, theinstrument “tumbles” or “spills” and no longer givesthe correct indication until reset. After spilling, it maybe reset with the caging knob. Many of the moderninstruments used are designed in such a manner thatthey will not tumble.

Instrument Check—As the gyro spools up, make surethere are no abnormal sounds. While taxiing, the instrumentshould indicate turns in the correct direction, and precession should not be abnormal. At idle power settings, the gyroscopic instruments using the vacuumsystem might not be up to operating speeds and preces-sion might occur more rapidly than during flight.

MAGNETIC COMPASSSince the magnetic compass works on the principle ofmagnetism, it is well for the pilot to have at least a basicunderstanding of magnetism. A simple bar magnet hastwo centers of magnetism which are called poles. Lines

of magnetic force flow out from each pole in all direc-tions, eventually bending around and returning to theother pole. The area through which these lines of forceflow is called the field of the magnet. For the purposeof this discussion, the poles are designated “north” and“south.” If two bar magnets are placed near each other,the north pole of one will attract the south pole of theother. There is evidence that there is a magnetic fieldsurrounding the Earth, and this theory is applied in thedesign of the magnetic compass. It acts very much asthough there were a huge bar magnet running along theaxis of the Earth which ends several hundred milesbelow the surface. [Figure 6-19]

The geographic north and south poles form the axis forthe Earth’s rotation. These positions are also referred toas true north and south. Another axis is formed by themagnetic north and south poles. Lines of magneticforce flow out from each pole in all directions, andeventually return to the opposite pole. A compassaligns itself with the magnetic axis formed by thenorth/south magnetic field of the Earth.

The lines of force have a vertical component (or pull)which is zero at the Equator, but builds to 100 percent ofthe total force at the magnetic poles. If magnetic needles,such as in the airplane’s magnetic compass, are heldalong these lines of force, the vertical component

N

S

N

S

North Magnetic Pole Geographic North Pole

The Earth's magnetic field comparedto a bar magnet.

Magnetic field around abar magnet.

Figure 6-19. Earth’s magnetic field.

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causes one end of the needle to dip or deflect downward. The amount of dip increases as the needlesare moved closer and closer to the poles. It is thisdeflection, or dip, that causes some of the larger compass errors.

The magnetic compass, which is usually the only direction-seeking instrument in the airplane, is simplein construction. It contains two steel magnetized needles fastened to a float, around which is mounted acompass card. The needles are parallel, with theirnorth-seeking ends pointing in the same direction. Thecompass card has letters for cardinal headings, andeach 30° interval is represented by a number, the lastzero of which is omitted. For example, 30° appears as a3 and 300° appears as a 30. Between these numbers,the card is graduated for each 5°. The magnetic compass is required equipment in all airplanes. It isused to set the gyroscopic heading indicator, correct forprecession, and as a backup in the event the headingindicator(s) fails. [Figure 6-20]

COMPASS ERRORSVARIATIONAlthough the magnetic field of the Earth lies roughlynorth and south, the Earth’s magnetic poles do not coincide with its geographic poles, which are used inthe construction of aeronautical charts. Consequently,at most places on the Earth’s surface, the direction-sensitive steel needles that seek the Earth’s magneticfield will not point to true north, but to magnetic north.Furthermore, local magnetic fields from mineraldeposits and other conditions may distort the Earth’smagnetic field, and cause additional error in the

position of the compass’ north-seeking magnetizedneedles with reference to true north.

The angular difference between magnetic north, thereference for the magnetic compass, and true north isvariation. Lines that connect points of equal variationare called isogonic lines. The line connecting pointswhere the magnetic variation is zero is an agonic line.To convert from true courses or headings to magnetic,subtract easterly variation and add westerly variation.Reverse the process to convert from magnetic to true.[Figure 6-21]

InstrumentLamp

Float Expansion Unit

OuterCase

Filler Hole

CompensatingMagnetCompass Card

Lubber Line

CompensatingScrews

SensingMagnet

Lens

Card

Lubber Line

Figure 6-20. Magnetic compass.

A

TrueNorth Pole

MagneticNorth Pole

AgonicLine

20°

20°

15°

15°

10° 5°

5°0°

Isogonic Lines

17°

10°

Figure 6-21. Variation at point A in the western United Statesis 17°. Since the magnetic north pole is located to the east ofthe true north pole in relation to this point, the variation iseasterly. When the magnetic pole falls to the west of the truenorth pole, variation is westerly.

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COMPASS DEVIATIONBesides the magnetic fields generated by the Earth,other magnetic fields are produced by metal and elec-trical accessories within the airplane. These magneticfields distort the Earth’s magnetic force, and causethe compass to swing away from the correct heading.This error is called deviation. Manufacturers installcompensating magnets within the compass housingto reduce the effects of deviation. The magnets areusually adjusted while the engine is running and allelectrical equipment is operating. However, it is notpossible to completely eliminate deviation error;therefore, a compass correction card is mounted nearthe compass. This card corrects for deviation thatoccurs from one heading to the next as the lines offorce interact at different angles. [Figure 6-22]

MAGNETIC DIPMagnetic dip is the result of the vertical component ofthe Earth’s magnetic field. This dip is virtually non-existent at the magnetic equator, since the lines offorce are parallel to the Earth’s surface and the verticalcomponent is minimal. When a compass is movedtoward the poles, the vertical component increases, and magnetic dip becomes more apparent at higher latitudes. Magnetic dip is responsible for compasserrors during acceleration, deceleration, and turns.

USING THE MAGNETIC COMPASS

ACCELERATION/DECELERATION ERRORSAcceleration and deceleration errors are fluctuations inthe compass during changes in speed. In the NorthernHemisphere, the compass swings towards the northduring acceleration, and towards the south duringdeceleration. When the speed stabilizes, the compassreturns to an accurate indication. This error is most pronounced when flying on a heading of east or west,and decreases gradually when flying closer to a northor south heading. The error does not occur when flyingdirectly north or south. The memory aid, ANDS(Accelerate North, Decelerate South) may help inrecalling this error. In the Southern Hemisphere, thiserror occurs in the opposite direction.

TURNING ERRORSTurning errors are most apparent when turning to orfrom a heading of north or south. This error increasesas the poles are neared and magnetic dip becomes moreapparent. There is no turning error when flying near themagnetic equator.

In the Northern Hemisphere, when making a turn froma northerly heading, the compass gives an initial indication of a turn in the opposite direction. It thenbegins to show the turn in the proper direction, but lagsbehind the actual heading. The amount of lag decreasesas the turn continues, then disappears as the airplanereaches a heading of east or west. When turning from aheading of east or west to a heading of north, there isno error as the turn begins. However, as the headingapproaches north, the compass increasingly lags behindthe airplane’s actual heading. When making a turn froma southerly heading, the compass gives an indicationof a turn in the correct direction, but leads the actualheading. This error also disappears as the airplaneapproaches an east or west heading. Turning from eastor west to a heading of south causes the compass tomove correctly at the start of a turn, but then it increas-ingly leads the actual heading as the airplane nears asoutherly direction.

The amount of lead or lag is approximately equal tothe latitude of the airplane. For example, if turningfrom a heading of south to a heading of west whileflying at 40° north latitude, the compass rapidly turnsto a heading of 220° (180° + 40°). At the midpoint ofthe turn, the lead decreases to approximately half(20°), and upon reaching a heading of west, it is zero.

The magnetic compass, which is the only direction-seek-ing instrument in the airplane, should be read only whenthe airplane is flying straight and level at a constant speed.This will help reduce errors to a minimum.

If the pilot thoroughly understands the errors and charac-teristics of the magnetic compass, this instrument canbecome the most reliable means of determining headings.

FOR (MH)

STEER (CH)

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330°

359° 30° 60° 88° 120° 152° 183° 212° 240° 268° 300° 329°

RADIO ON RADIO OFF✓

Figure 6-22. Compass correction card.

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Instrument Check—Prior to flight, make sure that thecompass is full of fluid. Then during turns, the compassshould swing freely and indicate known headings.

VERTICAL CARD COMPASSA newer design, the vertical card compass significantlyreduces the inherent error of the older compass designs.It consists of an azimuth on a rotating vertical card, andresembles a heading indicator with a fixed miniatureairplane to accurately present the heading of the air-plane. The presentation is easy to read, and the pilot cansee the complete 360° dial in relation to the airplaneheading. This design uses eddy current damping tominimize lead and lag during turns. [Figure 6-23]

OUTSIDE AIR TEMPERATURE GAUGEThe outside air temperature gauge (OAT) is a simpleand effective device mounted so that the sensingelement is exposed to the outside air. The sensingelement consists of a bimetallic-type thermometerin which two dissimilar materials are weldedtogether in a single strip and twisted into a helix.One end is anchored into protective tube and theother end is affixed to the pointer, which readsagainst the calibration on a circular face. OATgauges are calibrated in degrees Celsius, Fahrenheit, orboth. An accurate air temperature will provide the pilotwith useful information about temperature lapse ratewith altitude change. [Figure 6-24].

N

W

S

E

33

3024

21 15

126

3

Figure 6-23. Vertical card compass.

Eddy Current Damping—The decreased amplitude of oscillations bythe interaction of magnetic fields. In the case of a vertical card magneticcompass, flux from the oscillating permanent magnet produces eddycurrents in a damping disk or cup. The magnetic flux produced by theeddy currents opposes the flux from the permanent magnet anddecreases the oscillations.

Figure 6-24. Outside air temperature gauge.

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AIRPLANE FLIGHT MANUALSAn airplane flight manual is a document developed bythe airplane manufacturer and approved by the FederalAviation Administration (FAA). It is specific to a par-ticular make and model airplane by serial number andcontains operating procedures and limitations. Title14 of the Code of Federal Regulations (14 CFR) part91 requires that pilots comply with the operatinglimitations specified in the approved airplane flightmanuals, markings, and placards. Originally, flightmanuals followed whatever format and content themanufacturer felt was appropriate. This changed withthe acceptance of the General Aviation ManufacturersAssociation’s (GAMA) Specification for Pilot’sOperating Handbook, which established a standard-ized format for all general aviation airplane androtorcraft flight manuals. The Pilot’s OperatingHandbook (POH) is developed by the airplane manu-facturer and contains the FAA-approved AirplaneFlight Manual (AFM) information. However, ifPilot’s Operating Handbook is used as the main titleinstead of Airplane Flight Manual, a statement mustbe included on the title page indicating that sectionsof the document are FAA-approved as the AirplaneFlight Manual. [Figure 7-1]

An airplane owner/information manual is a documentdeveloped by the airplane manufacturer containing gen-eral information about the make and model of airplane.The airplane owner’s manual is not FAA-approved andis not specific to a particular serial numbered airplane.This manual provides general information about theoperation of the airplane and is not kept current, andtherefore cannot be substituted for the AFM/POH.

Besides the preliminary pages, a POH may contain asmany as ten sections. These sections are: General;

Limitations; Emergency Procedures; Normal Pro-cedures; Performance; Weight and Balance/EquipmentList; Systems Description; Handling, Service, andMaintenance; and Supplements. Manufacturers havethe option of including a tenth section on Safety Tips,as well as an alphabetical index at the end of the POH.

PRELIMINARY PAGESWhile the AFM/POH may appear similar for the samemake and model of airplane, each manual is uniquesince it contains specific information about a particularairplane, such as the equipment installed and weightand balance information. Therefore, manufacturers arerequired to include the serial number and registrationon the title page to identify the airplane to which themanual belongs. If a manual does not indicate a spe-cific airplane registration and serial number, it islimited to general study purposes only.

Most manufacturers include a table of contents, whichidentifies the order of the entire manual by section

Figure 7-1. Airplane Flight Manuals.

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number and title. Usually, each section also contains itsown table of contents. Page numbers reflect the sectionand page within that section (1-1, 1-2, 2-1, 3-1, and soforth). If the manual is published in loose-leaf form,each section is usually marked with a divider tab indi-cating the section number or title, or both. TheEmergency Procedures section may have a red tab forquick identification and reference.

GENERAL (SECTION 1)The General section provides the basic descriptiveinformation on the airplane and powerplant(s). Somemanuals include a three-view drawing of the airplanethat provides dimensions of various components.Included are such items as wingspan, maximum height,overall length, wheelbase length, main landing geartrack width, maximum propeller diameter, propellerground clearance, minimum turning radius, and wingarea. This section serves as a quick reference in becom-ing familiar with the airplane.

The last segment of the General section contains defi-nitions, abbreviations, explanations of symbology, andsome of the terminology used in the POH. At the optionof the manufacturer, metric and other conversion tablesmay also be included.

LIMITATIONS (SECTION 2)The Limitations section contains only those limitationsrequired by regulation or that are necessary for the safeoperation of the airplane, powerplant, systems, andequipment. It includes operating limitations, instru-ment markings, color-coding, and basic placards. Someof the limitation areas are: airspeed, powerplant, weightand loading distribution, and flight.

AIRSPEEDAirspeed limitations are shown on the airspeed indicatorby color-coding and on placards or graphs in the air-plane. [Figure 7-2] A red line on the airspeed indicatorshows the airspeed limit beyond which structural damagecould occur. This is called the never-exceed speed(VNE). A yellow arc indicates the speed range betweenmaximum structural cruising speed (VNO) and VNE.Operation of the airplane in the yellow airspeed arc isfor smooth air only, and then with caution. A green arcdepicts the normal operating speed range, with theupper end at VNO, and the lower end at stalling speed atmaximum weight with the landing gear and flapsretracted (VS1). The flap operating range is depicted bythe white arc, with the upper end at the maximum flapextended speed (VFE), and the lower end at the stallingspeed with the landing gear and flaps in the landingconfiguration (VSO).

In addition to the markings listed above, small multi-engine airplanes will have a red radial line to indicatesingle-engine minimum controllable airspeed (VMC). A

blue radial line is used to indicate single-engine bestrate-of-climb speed at maximum weight at sea level(VYSE).

POWERPLANTThe Powerplant Limitations area describes operatinglimitations on the airplane’s reciprocating or turbineengine(s). These include limitations for takeoff power,maximum continuous power, and maximum normaloperating power, which is the maximum power theengine can produce without any restrictions, and isdepicted by a green arc. Other items that can beincluded in this area are the minimum and maximumoil and fuel pressures, oil and fuel grades, and propelleroperating limits. [Figure 7-3]

Figure 7-3. Minimum, maximum, and normal operating rangemarkings on oil gauge.

All reciprocating-engine powered airplanes must havean r.p.m. indicator for each engine. Airplanes equippedwith a constant-speed propeller use a manifold pres-sure gauge to monitor power output and an r.p.m. gaugeto monitor propeller speed. Both instruments depict themaximum operating limit with a red radial line and thenormal operating range with a green arc. Some instru-ments may have a yellow arc to indicate a caution area.[Figure 7-4]

WEIGHT AND LOADING DISTRIBUTIONThe Weight and Loading Distribution area contains themaximum certificated weights, as well as the center-of-gravity (CG) range. The location of the referencedatum used in balance computations is included in this

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Figure 7-2. Airspeed limitations are depicted by colored arcsand radial lines.

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section. Weight and balance computations are not pro-vided in this area, but rather in the Weight and Balancesection of the AFM/POH.

FLIGHT LIMITSThis area lists authorized maneuvers with appropriateentry speeds, flight load factor limits, and kinds ofoperation limits. It also indicates those maneuvers thatare prohibited, such as spins, acrobatic flight, andoperational limitations such as flight into known icingconditions.

PLACARDSMost airplanes display one or more placards that con-tain information having a direct bearing on the safeoperation of the airplane. These placards are locatedin conspicuous places within the airplane and arereproduced in the Limitations section or as directedby an Airworthiness Directive (AD). [Figure 7-5]

Figure 7-5. Placards are a common method of depicting air-plane limitations.

EMERGENCY PROCEDURES (SECTION 3)Checklists describing the recommended proceduresand airspeeds for coping with various types of

emergencies or critical situations are located in theEmergency Procedures section. Some of the emergen-cies covered include: engine failure, fires, and systemsfailures. The procedures for in-flight engine restartingand ditching may also be included.

Manufacturers may first show the emergencies check-lists in an abbreviated form with the order of itemsreflecting the sequence of action. Amplified checkliststhat provide additional information on the proceduresfollow the abbreviated checklist. To be prepared foremergency situations, memorize the immediate actionitems and after completion, refer to the appropriatechecklist.

Manufacturers may include an optional area titled“Abnormal Procedures.” This section describes recom-mended procedures for handling malfunctions that arenot considered emergencies in nature.

NORMAL PROCEDURES (SECTION 4)This section begins with a listing of the airspeeds fornormal operations. The next area consists of severalchecklists that may include preflight inspection, beforestarting procedures, starting engine, before taxiing,taxiing, before takeoff, takeoff, climb, cruise, descent,before landing, balked landing, after landing, and post-flight procedures. An Amplified Procedures areafollows the checklists to provide more detailedinformation about the various procedures.

To avoid missing important steps, always use theappropriate checklists whenever they are available.Consistent adherence to approved checklists is a signof a disciplined and competent pilot.

PERFORMANCE (SECTION 5)The Performance section contains all the informationrequired by the aircraft certification regulations, andany additional performance information the manufac-turer feels may enhance a pilot’s ability to safely operatethe airplane. Performance charts, tables, and graphs varyin style, but all contain the same basic information. Someexamples of the performance information found in mostflight manuals include a graph or table for convertingcalibrated airspeed into true airspeed; stall speeds invarious configurations; and data for determining takeoffand climb performance, cruise performance, and landingperformance. Figure 7-6 is an example of a typicalperformance graph. For more information on how touse the charts, graphs, and tables, refer to Chapter 9—Aircraft Performance.

WEIGHT AND BALANCE/EQUIPMENT LIST(SECTION 6)The Weight and Balance/Equipment List sectioncontains all the information required by the FAA tocalculate the weight and balance of the airplane.

������������ � ���������

Figure 7-4. Manifold pressure and r.p.m. indicators.

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Manufacturers include sample weight and balanceproblems. Weight and balance is discussed in greaterdetail in Chapter 8—Weight and Balance.

SYSTEMS DESCRIPTION (SECTION 7)The Systems Description section is where the manu-facturer describes the systems in enough detail for thepilot to understand how the systems operate. For moreinformation on airplane systems, refer to Chapter5Aircraft Systems.

HANDLING, SERVICE, AND MAINTENANCE(SECTION 8)The Handling, Service, and Maintenance sectiondescribes the maintenance and inspections recom-mended by the manufacturer and the regulations.Additional maintenance or inspections may berequired by the issuance of Airworthiness Directives(AD) applicable to the airplane, engine, propeller, andcomponents.

This section also describes preventive maintenance thatmay be accomplished by certificated pilots, as well asthe manufacturer’s recommended ground handlingprocedures. This includes considerations for hangar-ing, tie-down, and general storage procedures for theairplane.

SUPPLEMENTS (SECTION 9)The Supplements section describes pertinent infor-mation necessary to safely and efficiently operate theairplane when equipped with the various optionalsystems and equipment not provided with the standardairplane. Some of this information may be supplied bythe airplane manufacturer, or by the manufacturer ofthe optional equipment. The appropriate informationis inserted into the flight manual at the time theequipment is installed. Autopilots, navigation systems,and air-conditioning systems are examples of equipmentdescribed in this section.

Figure 7-6. Stall speed chart.

Airworthiness Directive (AD)—A regulatory notice that is sent out bythe FAA to the registered owners of aircraft informing them of thediscovery of a condition that keeps their aircraft from continuing to meetits conditions for airworthiness. For further information, see 14 CFRpart 39.

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SAFETY TIPS (SECTION 10)The Safety Tips section is an optional section con-taining a review of information that enhances the safeoperation of the airplane. Some examples of theinformation that might be covered include: physio-logical factors, general weather information, fuelconservation procedures, high altitude operations,and cold weather operations.

AIRCRAFT DOCUMENTS

CERTIFICATE OF AIRCRAFT REGISTRATIONBefore an aircraft can be flown legally, it must beregistered with the FAA Civil Aviation Registry. TheCertificate of Aircraft Registration, which is issuedto the owner as evidence of the registration, must becarried in the aircraft at all times. [Figure 7-7]

The Certificate of Aircraft Registration cannot be usedfor operations when:

• The aircraft is registered under the laws of aforeign country.

• The aircraft’s registration is canceled at thewritten request of the holder of the certificate.

• The aircraft is totally destroyed or scrapped.

• The ownership of the aircraft is transferred.

• The holder of the certificate loses United Statescitizenship.

For additional events, see 14 CFR section 47.41.

When one of the events listed in 14 CFR section 47.41occurs, the previous owner must notify the FAA by fill-ing in the back of the Certificate of AircraftRegistration, and mailing it to:

Federal Aviation AdministrationCivil Aviation Registry, AFS-750P.O. Box 25504Oklahoma City, OK 73125

A dealer’s aircraft registration certificate is anotherform of registration certificate, but is valid only for

Figure 7-7. AC Form 8050-3, Certificate of Aircraft Registration.

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required flight tests by the manufacturer or in flightsthat are necessary for the sale of the aircraft by themanufacturer or a dealer. The dealer must remove itwhen the aircraft is sold.

After compliance with 14 CFR section 47.31, the pinkcopy of the application for a Certificate of AircraftRegistration is authorization to operate an unregisteredaircraft for a period not to exceed 90 days. Since theaircraft is unregistered, it cannot be operated outside ofthe United States until a permanent Certificate ofAircraft Registration is received and placed in the air-craft.

The FAA does not issue any certificate of ownership orendorse any information with respect to ownership ona Certificate of Aircraft Registration.

NOTE: For additional information concerning theAircraft Registration Application or the Aircraft Bill ofSale, contact the nearest FAA Flight Standards DistrictOffice (FSDO).

AIRWORTHINESS CERTIFICATEAn Airworthiness Certificate is issued by a representa-tive of the FAA after the aircraft has been inspected,is found to meet the requirements of 14 CFR part 21,and is in condition for safe operation. TheAirworthiness Certificate must be displayed in the air-craft so it is legible to the passengers and crew when-ever it is operated. The Airworthiness Certificate is

transferred with the aircraft except when it is sold to aforeign purchaser.

A Standard Airworthiness Certificate is issued for air-craft type certificated in the normal, utility, acrobatic,commuter, and transport categories or for mannedfree balloons. Figure 7-8 illustrates a StandardAirworthiness Certificate, and an explanation of eachitem in the certificate follows.

Item 1 Nationality—The “N” indicates the air-craft is registered in the United States.Registration marks consist of a series of up to fivenumbers or numbers and letters. In this case,N2631A is the registration number assigned tothis airplane.

Item 2—Indicates the manufacturer, make, andmodel of the aircraft.

Item 3—Indicates the manufacturer’s serial num-ber assigned to the aircraft, as noted on the aircraftdata plate.

Item 4—Indicates the category in which the air-craft must be operated. In this case, it must beoperated in accordance with the limitationsspecified for the “NORMAL” category.

Figure 7-8. FAA Form 8100-2, Standard Airworthiness Certificate.

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Item 5—Indicates the aircraft conforms to itstype certificate and is considered in condition forsafe operation at the time of inspection andissuance of the certificate. Any exemptions fromthe applicable airworthiness standards are brieflynoted here and the exemption number given. Theword “NONE” is entered if no exemption exists.

Item 6—Indicates the Airworthiness Certificateis in effect indefinitely if the aircraft is main-tained in accordance with 14 CFR parts 21, 43,and 91, and the aircraft is registered in the UnitedStates.

Also included are the date the certificate wasissued and the signature and office identificationof the FAA representative.

A Standard Airworthiness Certificate remains in effectas long as the aircraft receives the required maintenanceand is properly registered in the United States. Flightsafety relies, in part, on the condition of the aircraft,which is determined by inspections performed bymechanics, approved repair stations, or manufacturerswho meet specific requirements of 14 CFR part 43.

A Special Airworthiness Certificate is issued for allaircraft certificated in other than the Standard classi-fications, such as Experimental, Restricted, Limited,Provisional, and Sport Pilot. When purchasing an aircraftclassified as other than Standard, it is recommended thatthe local FSDO be contacted for an explanation of thepertinent airworthiness requirements and the limitationsof such a certificate.

AIRCRAFT MAINTENANCEMaintenance is defined as the preservation, inspection,overhaul, and repair of an aircraft, including thereplacement of parts. A PROPERLY MAINTAINEDAIRCRAFT IS A SAFE AIRCRAFT. In addition, reg-ular and proper maintenance ensures that an aircraftmeets an acceptable standard of airworthiness through-out its operational life.

Although maintenance requirements vary for differenttypes of aircraft, experience shows that aircraft needsome type of preventive maintenance every 25 hours offlying time or less, and minor maintenance at least every100 hours. This is influenced by the kind of operation,climatic conditions, storage facilities, age, and construc-tion of the aircraft. Manufacturers supply maintenancemanuals, parts catalogs, and other service informationthat should be used in maintaining the aircraft.

AIRCRAFT INSPECTIONS14 CFR part 91 places primary responsibility on theowner or operator for maintaining an aircraft in an

airworthy condition. Certain inspections must be per-formed on the aircraft, and the owner must maintainthe airworthiness of the aircraft during the timebetween required inspections by having any defectscorrected.

14 CFR part 91, subpart E, requires the inspection ofall civil aircraft at specific intervals to determine theoverall condition. The interval depends upon thetype of operations in which the aircraft is engaged.Some aircraft need to be inspected at least once each12-calendar months, while inspection is required forothers after each 100 hours of operation. In someinstances, an aircraft may be inspected in accordancewith an inspection system set up to provide for totalinspection of the aircraft on the basis of calendar time,time in service, number of system operations, or anycombination of these.

All inspections should follow the current manufac-turer’s maintenance manual, including the Instructionsfor Continued Airworthiness concerning inspectionsintervals, parts replacement, and life-limited items asapplicable to the aircraft.

ANNUAL INSPECTIONAny reciprocating-engine powered or single-engine-turbojet/turbo-propeller powered small aircraft (12,500pounds and under) flown for business or pleasure andnot flown for compensation or hire is required to beinspected at least annually. The inspection shall beperformed by a certificated airframe and powerplant(A&P) mechanic who holds an Inspection Authorization(IA), by the manufacturer, or by a certificated and appro-priately rated repair station. The aircraft may notbe operated unless the annual inspection has beenperformed within the preceding 12-calendar months. Aperiod of 12-calendar months extends from any day ofa month to the last day of the same month the followingyear. An aircraft overdue for an annual inspection maybe operated under a Special Flight Permit issued by theFAA for the purpose of flying the aircraft to a locationwhere the annual inspection can be performed.However, all applicable Airworthiness Directives thatare due must be complied with.

100-HOUR INSPECTIONAll aircraft under 12,500 pounds (except turbojet/turbo-propeller powered multiengine airplanes and turbinepowered rotorcraft), used to carry passengers for hire,must have received a 100-hour inspection within thepreceding 100 hours of time in service and have beenapproved for return to service. Additionally, an aircraftused for flight instruction for hire, when provided bythe person giving the flight instruction, must also havereceived a 100-hour inspection. This inspection mustbe performed by an FAA certificated A&P mechanic,an appropriately rated FAA certificated repair station,

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or by the aircraft manufacturer. An annual inspection,or an inspection for the issuance of an AirworthinessCertificate may be substituted for a required 100-hourinspection. The 100-hour limitation may be exceededby not more than 10 hours while en route to reach aplace where the inspection can be done. The excesstime used to reach a place where the inspection can bedone must be included in computing the next 100 hoursof time in service.

OTHER INSPECTION PROGRAMSThe annual and 100-hour inspection requirements donot apply to large (over 12,500 pounds) airplanes,turbojets, or turbo-propeller powered multiengineairplanes or to aircraft for which the owner complieswith a progressive inspection program. Details of theserequirements may be determined by reference to 14CFR part 43, section 43.11 and part 91, subpart E, andby inquiring at a local FSDO.

ALTIMETER SYSTEM INSPECTION14 CFR part 91, section 91.411 requires that the altime-ter, encoding altimeter, and related system be testedand inspected in the preceding 24 months beforeoperated in controlled airspace under instrumentflight rules (IFR).

TRANSPONDER INSPECTION14 CFR part 91, section 91.413 requires that before atransponder can be used under 14 CFR part 91, section91.215(a), it shall be tested and inspected within thepreceding 24 months.

PREFLIGHT INSPECTIONSThe preflight inspection is a thorough and systematicmeans by which a pilot determines if the aircraft is air-worthy and in condition for safe operation. POHs andowner/information manuals contain a section devotedto a systematic method of performing a preflightinspection.

MINIMUM EQUIPMENT LISTS (MEL) AND OPERATIONS WITH INOPERATIVE EQUIPMENTThe Code of Federal Regulations (CFRs) requires thatall aircraft instruments and installed equipment areoperative prior to each departure. When the FAAadopted the minimum equipment list (MEL) con-cept for 14 CFR part 91 operations, this allowed forthe first time, operations with inoperative items deter-mined to be nonessential for safe flight. At the same

time, it allowed part 91 operators, without an MEL, todefer repairs on nonessential equipment within theguidelines of part 91.

There are two primary methods of deferring main-tenance on small rotorcraft, non-turbine poweredairplanes, gliders, or lighter-than-air aircraft operatedunder part 91. They are the deferral provision of 14CFR part 91, section 91.213(d) and an FAA-approvedMEL.

The deferral provision of section 91.213(d) is widelyused by most pilot/operators. Its popularity is due tosimplicity and minimal paperwork. When inoperativeequipment is found during preflight or prior to depar-ture, the decision should be to cancel the flight, obtainmaintenance prior to flight, or to defer the item orequipment.

Maintenance deferrals are not used for in-flight dis-crepancies. The manufacturer’s AFM/POH proceduresare to be used in those situations. The discussion thatfollows assumes that the pilot wishes to defer mainte-nance that would ordinarily be required prior to flight.

Using the deferral provision of section 91.213(d), thepilot determines whether the inoperative equipment isrequired by type design, the CFRs, or ADs. If theinoperative item is not required, and the aircraft canbe safely operated without it, the deferral may be made.The inoperative item shall be deactivated or removedand an INOPERATIVE placard placed near the appro-priate switch, control, or indicator. If deactivation orremoval involves maintenance (removal always will),it must be accomplished by certificated maintenancepersonnel.

For example, if the position lights (installed equipment)were discovered to be inoperative prior to a daytimeflight, the pilot would follow the requirements ofsection 91.213(d).

The deactivation may be a process as simple as the pilotpositioning a circuit breaker to the OFF position, or ascomplex as rendering instruments or equipment totallyinoperable. Complex maintenance tasks require a cer-tificated and appropriately rated maintenance person toperform the deactivation. In all cases, the item orequipment must be placarded INOPERATIVE.

Minimum Equipment List (MEL)—An inventory of instruments andequipment that may legally be inoperative, with the specific conditionsunder which an aircraft may be flown with such items inoperative.

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All small rotorcraft, non-turbine powered airplanes,gliders, or lighter-than-air aircraft operated under part91 are eligible to use the maintenance deferral provi-sions of section 91.213(d). However, once an operatorrequests an MEL, and a Letter of Authorization (LOA)is issued by the FAA, then the use of the MEL becomesmandatory for that aircraft. All maintenance deferralsmust be accomplished in accordance with the termsand conditions of the MEL and the operator-generatedprocedures document.

The use of an MEL for an aircraft operated under part91 also allows for the deferral of inoperative items orequipment. The primary guidance becomes the FAA-approved MEL issued to that specific operator andN-numbered aircraft.

The FAA has developed master minimum equipmentlists (MMELs) for aircraft in current use. Upon writtenrequest by an operator, the local FSDO may issue theappropriate make and model MMEL, along with anLOA, and the preamble. The operator then developsoperations and maintenance (O&M) procedures fromthe MMEL. This MMEL with O&M procedures nowbecomes the operator’s MEL. The MEL, LOA, pream-ble, and procedures document developed by the operatormust be on board the aircraft when it is operated.

The FAA considers an approved MEL to be a supple-mental type certificate (STC) issued to an aircraft byserial number and registration number. It thereforebecomes the authority to operate that aircraft in acondition other than originally type certificated.

With an approved MEL, if the position lights werediscovered inoperative prior to a daytime flight, thepilot would make an entry in the maintenance recordor discrepancy record provided for that purpose. Theitem is then either repaired or deferred in accordancewith the MEL. Upon confirming that daytime flightwith inoperative position lights is acceptable inaccordance with the provisions of the MEL, the pilotwould leave the position lights switch OFF, open thecircuit breaker (or whatever action is called for in theprocedures document), and placard the position lightswitch as INOPERATIVE.

There are exceptions to the use of the MEL for deferral.For example, should a component fail that is not listedin the MEL as deferrable (the tachometer, flaps, or stallwarning device, for example), then repairs are requiredto be performed prior to departure. If maintenance orparts are not readily available at that location, a specialflight permit can be obtained from the nearest FSDO.This permit allows the aircraft to be flown to anotherlocation for maintenance. This allows an aircraft thatmay not currently meet applicable airworthinessrequirements, but is capable of safe flight, to be

operated under the restrictive special terms and con-ditions attached to the special flight permit.

Deferral of maintenance is not to be taken lightly, anddue consideration should be given to the effect aninoperative component may have on the operation ofan aircraft, particularly if other items are inoperative.Further information regarding MELs and operationswith inoperative equipment can be found in AdvisoryCircular (AC) 91-67, Minimum Equipment Requirementsfor General Aviation Operations Under FAR Part 91.

PREVENTIVE MAINTENANCEPreventive maintenance is considered to be simple orminor preservation operations and the replacement ofsmall standard parts, not involving complex assemblyoperations. Certificated pilots, excluding student pilots,sport pilots, and recreational pilots, may performpreventive maintenance on any aircraft that is ownedor operated by them provided that aircraft is not usedin air carrier service. (Sport pilots operating lightsport aircraft, refer to 14 CFR part 65 for maintenanceprivileges.) 14 CFR part 43, Appendix A, contains a listof the operations that are considered to be preventivemaintenance.

REPAIRS AND ALTERATIONSRepairs and alterations are classified as either major orminor. 14 CFR part 43, Appendix A, describes thealterations and repairs considered major. Major repairsor alterations shall be approved for return to service onFAA Form 337, Major Repairs and Major Alterations,by an appropriately rated certificated repair station, anFAA certificated A&P mechanic holding an InspectionAuthorization, or a representative of the Administrator.Minor repairs and minor alterations may be approvedfor return to service with a proper entry in the mainte-nance records by an FAA certificated A&P mechanic oran appropriately certificated repair station.

For modifications of experimental aircraft, refer to theoperating limitations issued to that aircraft.Modifications in accordance with FAA Order 8130.2,Airworthiness Certification of Aircraft and RelatedProducts, may require the notification of the issuingauthority.

SPECIAL FLIGHT PERMITSA special flight permit is a Special AirworthinessCertificate issued authorizing operation of an aircraftthat does not currently meet applicable airworthinessrequirements but is safe for a specific flight. Before thepermit is issued, an FAA inspector may personallyinspect the aircraft, or require it to be inspected by anFAA certificated A&P mechanic or an appropriatelycertificated repair station, to determine its safety for theintended flight. The inspection shall be recorded in theaircraft records.

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The special flight permit is issued to allow the aircraftto be flown to a base where repairs, alterations, ormaintenance can be performed; for delivering orexporting the aircraft; or for evacuating an aircraft froman area of impending danger. A special flight permitmay be issued to allow the operation of an overweightaircraft for flight beyond its normal range over water orland areas where adequate landing facilities or fuel isnot available.

If a special flight permit is needed, assistance and thenecessary forms may be obtained from the local FSDOor Designated Airworthiness Representative (DAR).[Figure 7-9]

AIRWORTHINESS DIRECTIVESA primary safety function of the FAA is to requirecorrection of unsafe conditions found in an aircraft,aircraft engine, propeller, or appliance when suchconditions exist and are likely to exist or develop inother products of the same design. The unsafe conditionmay exist because of a design defect, maintenance, orother causes. 14 CFR part 39, Airworthiness Directives(ADs), defines the authority and responsibility of theAdministrator for requiring the necessary correctiveaction. ADs are the means used to notify aircraft ownersand other interested persons of unsafe conditions and tospecify the conditions under which the product maycontinue to be operated.

ADs may be divided into two categories:

1. those of an emergency nature requiring immediatecompliance prior to further flight, and

2. those of a less urgent nature requiring compliancewithin a specified period of time.

Airworthiness Directives are regulatory and shall becomplied with unless a specific exemption is granted.It is the aircraft owner or operator’s responsibility toensure compliance with all pertinent ADs. Thisincludes those ADs that require recurrent or continuingaction. For example, an AD may require a repetitiveinspection each 50 hours of operation, meaning theparticular inspection shall be accomplished andrecorded every 50 hours of time in service.Owners/operators are reminded there is no provisionto overfly the maximum hour requirement of an ADunless it is specifically written into the AD. To helpdetermine if an AD applies to an amateur-built aircraft,contact the local FSDO.

14 CFR part 91, section 91.417 requires a record to bemaintained that shows the current status of applicableADs, including the method of compliance; the ADnumber and revision date, if recurring; the time anddate when due again; the signature; kind of certificate;and certificate number of the repair station or mechanicwho performed the work. For ready reference, many

Figure 7-9. FAA Form 8130-7, Special Airworthiness Certificate.

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aircraft owners have a chronological listing of the per-tinent ADs in the back of their aircraft, engine, andpropeller maintenance records.

All Airworthiness Directives and the AD Biweekly arefree on the Internet at www.airweb.faa.gov/rgl

Paper copies of the Summary of AirworthinessDirectives and the AD Biweekly may be purchasedfrom the Superintendent of Documents. The Summarycontains all the valid ADs previously published and isdivided into two areas. The small aircraft and rotorcraftbooks contain all ADs applicable to small aircraft(12,500 pounds or less maximum certificated takeoffweight) and ADs applicable to all helicopters. The largeaircraft books contain all ADs applicable to large air-craft.

For further information on how to order ADs and thecurrent price, contact:

U.S. Department of TransportationFederal Aviation AdministrationDelegation & Airworthiness Programs Branch,AIR-140P.O. Box 26460Oklahoma City, OK 73125Telephone Number: (405) 954-4103Fax: (405) 954-4104

AIRCRAFT OWNER/OPERATORRESPONSIBILITIESThe registered owner/operator of an aircraft isresponsible for certain items such as:

• Having a current Airworthiness Certificate and aCertificate of Aircraft Registration in the aircraft.

• Maintaining the aircraft in an airworthycondition, including compliance with allapplicable Airworthiness Directives.

• Assuring that maintenance is properly recorded.

• Keeping abreast of current regulations concern-ing the operation and maintenance of the aircraft.

• Notifying the FAA Civil Aviation Registryimmediately of any change of permanent mailingaddress, or of the sale or export of the aircraft, orof the loss of the eligibility to register an aircraft.(Refer to 14 CFR part 47, section 47.41.)

• Having a current FCC radio station license ifequipped with radios, including emergencylocator transmitter (ELT), if operated outside ofthe United States.

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Compliance with the weight and balance limits of anyairplane is critical to flight safety. Operating an airplaneabove the maximum weight limitation compromisesthe structural integrity of the airplane and adverselyaffects its performance. Operation with the center ofgravity (CG) outside the approved limits may result incontrol difficulty.

WEIGHT CONTROLWeight is the force with which gravity attracts a bodytoward the center of the earth. It is a product of themass of a body and the acceleration acting on the body.Weight is a major factor in airplane construction andoperation, and demands respect from all pilots.

The force of gravity continually attempts to pull the air-plane down toward earth. The force of lift is the onlyforce that counteracts weight and sustains the airplanein flight. However, the amount of lift produced by anairfoil is limited by the airfoil design, angle of attack,airspeed, and air density. Therefore, to assure that thelift generated is sufficient to counteract weight, loadingthe airplane beyond the manufacturer’s recommendedweight must be avoided. If the weight is greater thanthe lift generated, the airplane may be incapable offlight.

EFFECTS OF WEIGHTAny item aboard the airplane that increases the totalweight is undesirable as far as performance is con-cerned. Manufacturers attempt to make the airplane aslight as possible without sacrificing strength or safety.

The pilot of an airplane should always be aware of theconsequences of overloading. An overloaded airplanemay not be able to leave the ground, or if it doesbecome airborne, it may exhibit unexpected and

unusually poor flight characteristics. If an airplane isnot properly loaded, the initial indication of poor per-formance usually takes place during takeoff.

Excessive weight reduces the flight performance of anairplane in almost every respect. The most importantperformance deficiencies of the overloaded airplaneare:

• Higher takeoff speed.

• Longer takeoff run.

• Reduced rate and angle of climb.

• Lower maximum altitude.

• Shorter range.

• Reduced cruising speed.

• Reduced maneuverability.

• Higher stalling speed.

• Higher approach and landing speed.

• Longer landing roll.

• Excessive weight on the nosewheel or tailwheel.

The pilot must be knowledgeable in the effect of weighton the performance of the particular airplane beingflown. Preflight planning should include a check ofperformance charts to determine if the airplane’sweight may contribute to hazardous flight operations.Excessive weight in itself reduces the safety marginsavailable to the pilot, and becomes even more hazardouswhen other performance-reducing factors are combinedwith overweight. The pilot must also consider the con-sequences of an overweight airplane if an emergency

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condition arises. If an engine fails on takeoff or air-frame ice forms at low altitude, it is usually too late toreduce the airplane’s weight to keep it in the air.

WEIGHT CHANGESThe weight of the airplane can be changed by alteringthe fuel load. Gasoline has considerable weight—6pounds per gallon—30 gallons may weigh more thanone passenger. But it must be remembered that ifweight is lowered by reducing fuel, the range of the air-plane is decreased. During flight, fuel burn is normallythe only weight change that takes place. As fuel is used,the airplane becomes lighter and performance isimproved.

Changes of fixed equipment have a major effect uponthe weight of the airplane. An airplane can be over-loaded by the installation of extra radios or instruments.Repairs or modifications may also affect the weight ofthe airplane.

BALANCE, STABILITY, AND CENTER OF GRAVITYBalance refers to the location of the center of gravity(CG) of an airplane, and is important to airplane sta-bility and safety in flight. The center of gravity is apoint at which an airplane would balance if it weresuspended at that point.

The prime concern of airplane balancing is the foreand aft location of the CG along the longitudinal axis.The center of gravity is not necessarily a fixed point;its location depends on the distribution of weight inthe airplane. As variable load items are shifted orexpended, there is a resultant shift in CG location. Thepilot should realize that if the CG of an airplane is dis-placed too far forward on the longitudinal axis, anose-heavy condition will result. Conversely, if theCG is displaced too far aft on the longitudinal axis, atail-heavy condition will result. It is possible that anunfavorable location of the CG could produce such anunstable condition that the pilot could not control theairplane. [Figure 8-1]

Location of the CG with reference to the lateral axis isalso important. For each item of weight existing to theleft of the fuselage centerline, there is an equal weightexisting at a corresponding location on the right. Thismay be upset, however, by unbalanced lateral loading.The position of the lateral CG is not computed, but thepilot must be aware that adverse effects will certainlyarise as a result of a laterally unbalanced condition.Lateral unbalance will occur if the fuel load is misman-aged by supplying the engine(s) unevenly from tankson one side of the airplane. The pilot can compensatefor the resulting wing-heavy condition by adjusting theaileron trim tab or by holding a constant aileron control

pressure. However, this places the airplane controls inan out-of-streamline condition, increases drag, andresults in decreased operating efficiency. Since lateralbalance is relatively easy to control and longitudinalbalance is more critical, further reference to balance inthis handbook will mean longitudinal location of thecenter of gravity.

In any event, flying an airplane that is out of balancecan produce increased pilot fatigue with obviouseffects on the safety and efficiency of flight. The pilot’snatural correction for longitudinal unbalance is a changeof trim to remove the excessive control pressure.Excessive trim, however, has the effect of not onlyreducing aerodynamic efficiency but also reducingprimary control travel distance in the direction thetrim is applied.

EFFECTS OF ADVERSE BALANCEAdverse balance conditions affect airplane flightcharacteristics in much the same manner as thosementioned for an excess weight condition. In addition,there are two essential airplane characteristics that maybe seriously affected by improper balance; these arestability and control. Loading in a nose-heavy condi-tion causes problems in controlling and raising thenose, especially during takeoff and landing. Loadingin a tail-heavy condition has a most serious effectupon longitudinal stability, and can reduce the airplane’scapability to recover from stalls and spins. Anotherundesirable characteristic produced from tail-heavyloading is that it produces very light control forces. Thismakes it easy for the pilot to inadvertently overstress theairplane.

Limits for the location of the airplane’s center of grav-ity are established by the manufacturer. These are thefore and aft limits beyond which the CG should not belocated for flight. These limits are published for eachairplane in the Type Certificate Data Sheet, or AircraftSpecification and the Airplane Flight Manual or Pilot’s

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Figure 8-1. Lateral or longitudinal unbalance.

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Operating Handbook (AFM/POH). If, after loading, theCG is not within the allowable limits, it will be neces-sary to relocate some items within the airplane beforeflight is attempted.

The forward center-of-gravity limit is often establishedat a location that is determined by the landing charac-teristics of the airplane. During landing, which is oneof the most critical phases of flight, exceeding theforward CG limit may result in excessive loads onthe nosewheel; a tendency to nose over on tailwheel-type airplanes; decreased performance; higherstalling speeds; and higher control forces. In extremecases, a CG location that is forward of the forward limitmay result in nose heaviness to the extent that it maybe difficult or impossible to flare for landing.Manufacturers purposely place the forward CG limitas far rearward as possible to aid pilots in avoidingdamage to the airplane when landing. In addition todecreased static and dynamic longitudinal stability,other undesirable effects caused by a CG location aftof the allowable range may include extreme controldifficulty, violent stall characteristics, and very lightstick forces that make it easy to overstress the airplaneinadvertently.

A restricted forward center-of-gravity limit is alsospecified to assure that sufficient elevator deflection isavailable at minimum airspeed. When structural limi-tations or large stick forces do not limit the forwardCG position, it is located at the position where full-upelevator is required to obtain a high angle of attack forlanding.

The aft center-of-gravity limit is the most rearwardposition at which the CG can be located for the mostcritical maneuver or operation. As the CG moves aft,a less stable condition occurs, which decreases theability of the airplane to right itself after maneuveringor turbulence.

For some airplanes the CG limits, both fore and aft,may be specified to vary as gross weight changes. Theymay also be changed for certain operations such asacrobatic flight, retraction of the landing gear, or theinstallation of special loads and devices that change theflight characteristics.

The actual location of the CG can be altered by manyvariable factors and is usually controlled by the pilot.Placement of baggage and cargo items determines theCG location. The assignment of seats to passengerscan also be used as a means of obtaining a favorablebalance. If the airplane is tail-heavy, it is only logicalto place heavy passengers in forward seats. Also, fuelburn can affect the CG based on the location of the fueltanks.

MANAGEMENT OF WEIGHT AND BALANCECONTROLWeight and balance control should be a matter of con-cern to all pilots. The pilot has control over loadingand fuel management (the two variable factors thatcan change both total weight and CG location) of aparticular airplane.

The airplane owner or operator should make certainthat up-to-date information is available in the airplanefor the pilot’s use, and should ensure that appropriateentries are made in the airplane records when repairs ormodifications have been accomplished. Weightchanges must be accounted for and the proper notationsmade in weight and balance records. The equipmentlist must be updated, if appropriate. Without such infor-mation, the pilot has no foundation upon which to basethe necessary calculations and decisions.

Before any flight, the pilot should determine theweight and balance condition of the airplane. Simpleand orderly procedures, based on sound principles,have been devised by airplane manufacturers for thedetermination of loading conditions. The pilot mustuse these procedures and exercise good judgment. Inmany modern airplanes, it is not possible to fill allseats, baggage compartments, and fuel tanks, and stillremain within the approved weight and balance limits.If the maximum passenger load is carried, the pilotmust often reduce the fuel load or reduce the amountof baggage.

TERMS AND DEFINITIONSThe pilot should be familiar with terms used in workingthe problems related to weight and balance. The follow-ing list of terms and their definitions is well standardized,and knowledge of these terms will aid the pilot to betterunderstand weight and balance calculations of anyairplane. Terms defined by the General AviationManufacturers Association as an industry standard aremarked in the titles with GAMA.

• Arm (moment arm)—is the horizontal distancein inches from the reference datum line to thecenter of gravity of an item. The algebraic sign isplus (+) if measured aft of the datum, and minus(–) if measured forward of the datum.

• Basic empty weight (GAMA)—includes thestandard empty weight plus optional and specialequipment that has been installed.

• Center of gravity (CG)—is the point aboutwhich an airplane would balance if it were possi-ble to suspend it at that point. It is the mass centerof the airplane, or the theoretical point at whichthe entire weight of the airplane is assumed to beconcentrated. It may be expressed in inches from

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the reference datum, or in percent of meanaerodynamic chord (MAC).

• Center-of-gravity limits—are the specified for-ward and aft points within which the CG must belocated during flight. These limits are indicatedon pertinent airplane specifications.

• Center-of-gravity range—is the distancebetween the forward and aft CG limits indicatedon pertinent airplane specifications.

• Datum (reference datum)—is an imaginary ver-tical plane or line from which all measurementsof arm are taken. The datum is established by themanufacturer. Once the datum has been selected,all moment arms and the location of CG range aremeasured from this point.

• Delta—is a Greek letter expressed by the symbol∆ to indicate a change of values. As an example,∆ CG indicates a change (or movement) of theCG.

• Floor load limit—is the maximum weight thefloor can sustain per square inch/foot as providedby the manufacturer.

• Fuel load—is the expendable part of the load ofthe airplane. It includes only usable fuel, not fuelrequired to fill the lines or that which remainstrapped in the tank sumps.

• Licensed empty weight—is the empty weightthat consists of the airframe, engine(s), unusablefuel, and undrainable oil plus standard andoptional equipment as specified in the equipmentlist. Some manufacturers used this term prior toGAMA standardization.

• Maximum landing weight—is the greatestweight that an airplane normally is allowed tohave at landing.

• Maximum ramp weight—is the total weight ofa loaded aircraft, and includes all fuel. It isgreater than the takeoff weight due to the fuel thatwill be burned during the taxi and runup opera-tions. Ramp weight may also be referred to as taxiweight.

• Maximum takeoff weight—is the maximumallowable weight for takeoff.

• Maximum weight—is the maximum authorizedweight of the aircraft and all of its equipment asspecified in the Type Certificate Data Sheets(TCDS) for the aircraft.

• Maximum zero fuel weight (GAMA)—is themaximum weight, exclusive of usable fuel.

• Mean aerodynamic chord (MAC)—is the aver-age distance from the leading edge to the trailingedge of the wing.

• Moment—is the product of the weight of an itemmultiplied by its arm. Moments are expressed inpound-inches (lb-in). Total moment is the weightof the airplane multiplied by the distance betweenthe datum and the CG.

• Moment index (or index)—is a moment dividedby a constant such as 100, 1,000, or 10,000. Thepurpose of using a moment index is to simplifyweight and balance computations of airplaneswhere heavy items and long arms result in large,unmanageable numbers.

• Payload (GAMA)—is the weight of occupants,cargo, and baggage.

• Standard empty weight (GAMA)—consists ofthe airframe, engines, and all items of operatingequipment that have fixed locations and are per-manently installed in the airplane; including fixedballast, hydraulic fluid, unusable fuel, and fullengine oil.

• Standard weights—have been established fornumerous items involved in weight and balancecomputations. These weights should not be usedif actual weights are available. Some of the stan-dard weights are:

Gasoline . . . . . . . . . . . . . . . . . . . . . 6 lb/US galJet A, Jet A-1 . . . . . . . . . . . . . . . . 6.8 lb/US galJet B . . . . . . . . . . . . . . . . . . . . . . . 6.5 lb/US galOil . . . . . . . . . . . . . . . . . . . . . . . . 7.5 lb/US galWater . . . . . . . . . . . . . . . . . . . . . 8.35 lb/US gal

• Station—is a location in the airplane that is iden-tified by a number designating its distance ininches from the datum. The datum is, therefore,identified as station zero. An item located at sta-tion +50 would have an arm of 50 inches.

• Useful load—is the weight of the pilot, copilot,passengers, baggage, usable fuel, and drainableoil. It is the basic empty weight subtracted fromthe maximum allowable gross weight. This termapplies to general aviation aircraft only.

BASIC PRINCIPLES OF WEIGHT AND BALANCE COMPUTATIONSIt might be advantageous at this point to review anddiscuss some of the basic principles of how weight andbalance can be determined. The following method ofcomputation can be applied to any object or vehiclewhere weight and balance information is essential; but

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to fulfill the purpose of this handbook, it is directedprimarily toward the airplane.

By determining the weight of the empty airplane andadding the weight of everything loaded on the air-plane, a total weight can be determined. This is quitesimple; but to distribute this weight in such a mannerthat the entire mass of the loaded airplane is balancedaround a point (CG), which must be located withinspecified limits, presents a greater problem, particu-larly if the basic principles of weight and balance arenot understood.

The point where the airplane will balance can be deter-mined by locating the center of gravity, which is, asstated in the definitions of terms, the imaginary pointwhere all the weight is concentrated. To provide thenecessary balance between longitudinal stability andelevator control, the center of gravity is usuallylocated slightly forward of the center of lift. Thisloading condition causes a nose-down tendency inflight, which is desirable during flight at a high angleof attack and slow speeds.

A safe zone within which the balance point (CG) mustfall is called the CG range. The extremities of the rangeare called the forward CG limits and aft CG limits.These limits are usually specified in inches, along thelongitudinal axis of the airplane, measured from a datumreference. The datum is an arbitrary point, established byairplane designers, which may vary in location betweendifferent airplanes. [Figure 8-2]

Figure 8-2. Weight and balance illustrated.

The distance from the datum to any component partof the airplane, or any object loaded on the airplane,is called the arm. When the object or component islocated aft of the datum, it is measured in positiveinches; if located forward of the datum, it is measuredas negative inches, or minus inches. The location ofthe object or part is often referred to as the station. If

the weight of any object or component is multipliedby the distance from the datum (arm), the product isthe moment. The moment is the measurement of thegravitational force that causes a tendency of theweight to rotate about a point or axis and is expressedin pound-inches.

To illustrate, assume a weight of 50 pounds is placedon the board at a station or point 100 inches from thedatum. The downward force of the weight can be deter-mined by multiplying 50 pounds by 100 inches, whichproduces a moment of 5,000 lb-in. [Figure 8-3]

Figure 8-3. Determining moments.

To establish a balance, a total of 5,000 lb-in must beapplied to the other end of the board. Any combinationof weight and distance which, when multiplied, pro-duces a 5,000 lb-in moment will balance the board. Forexample, as illustrated in figure 8-4, if a 100-poundweight is placed at a point (station) 25 inches from thedatum, and another 50-pound weight is placed at apoint (station) 50 inches from the datum, the sum of theproduct of the two weights and their distances will totala moment of 5,000 lb-in, which will balance the board.

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8-6

WEIGHT AND BALANCE RESTRICTIONSThe airplane’s weight and balance restrictions shouldbe closely followed. The loading conditions and emptyweight of a particular airplane may differ from thatfound in the AFM/POH because modifications orequipment changes may have been made. Sampleloading problems in the AFM/POH are intended forguidance only; therefore, each airplane must betreated separately. Although an airplane is certifiedfor a specified maximum gross takeoff weight, it willnot safely take off with this load under all conditions.Conditions that affect takeoff and climb performancesuch as high elevations, high temperatures, and highhumidity (high-density altitudes) may require a reduc-tion in weight before flight is attempted. Other factorsto consider prior to takeoff are runway length, runwaysurface, runway slope, surface wind, and the presenceof obstacles. These factors may require a reduction inweight prior to flight.

Some airplanes are designed so that it is difficult toload them in a manner that will place the CG out oflimits. These are usually small airplanes with the seats,fuel, and baggage areas located near the CG limit.These airplanes, however, can be overloaded inweight.

Other airplanes can be loaded in such a manner thatthey will be out of CG limits even though the usefulload has not been exceeded.

Because of the effects of an out-of-balance or over-weight condition, a pilot should always be sure that anairplane is properly loaded.

DETERMINING LOADED WEIGHT ANDCENTER OF GRAVITYThere are various methods for determining the loadedweight and center of gravity of an aircraft. There is thecomputation method, as well as methods that utilizegraphs and tables provided by the aircraft manufac-turer.

COMPUTATIONAL METHODThe computational method involves the application ofbasic math functions. The following is an example ofthe computational method.

Given:

Maximum Gross Weight . . . . . . . . . . . . . . 3400 lbCenter-of-Gravity Range . . . . . . . . . . . . . 78-86 inFront Seat Occupants . . . . . . . . . . . . . . . . . . 340 lbRear Seat Occupants . . . . . . . . . . . . . . . . . . 350 lbFuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 galBaggage Area 1 . . . . . . . . . . . . . . . . . . . . . . . 80 lb

To determine the loaded weight and CG, follow thesesteps.

Step 1—List the weight of the airplane, occu-pants, fuel, and baggage. Remember that fuelweighs 6 pounds per gallon.

Step 2—Enter the moment for each item listed.Remember “weight x arm = moment.”

Step 3—Total the weight and moments.

Step 4—To determine the CG, divide the totalmoment by the total weight.

NOTE: The weight and balance records for a particularairplane will provide the empty weight and moment aswell as the information on the arm distance.

The total loaded weight of 3,320 pounds does notexceed the maximum gross weight of 3,400 pounds andthe CG of 84.8 is within the 78-86 inch range; there-fore, the airplane is loaded within limits.

GRAPH METHODAnother method for determining the loaded weight andCG is the use of graphs provided by the manufacturers.To simplify calculations, the moment may sometimesbe divided by 100, 1,000, or 10,000. The following isan example of the graph method. [Figures 8-5 and 8-6]

Given:

Front Seat Occupants . . . . . . . . . . . . . . . . . . 340 lbRear Seat Occupants . . . . . . . . . . . . . . . . . . 300 lbFuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 galBaggage Area 1 . . . . . . . . . . . . . . . . . . . . . . . 20 lb

The same steps should be followed as in the computa-tional method except the graphs provided will calculatethe moments and allow the pilot to determine if theairplane is loaded within limits. To determine the

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moment using the loading graph, find the weight anddraw a line straight across until it intercepts the itemfor which the moment is to be calculated. Then draw aline straight down to determine the moment. (The redline on the loading graph represents the moment for thepilot and front passenger. All other moments weredetermined in the same way.) Once this has been donefor each item, total the weight and moments and draw aline for both weight and moment on the center-of-grav-ity envelope graph. If the lines intersect within theenvelope, the airplane is loaded within limits. In thissample loading problem, the airplane is loaded withinlimits.

CH 08.qxd 10/24/03 7:07 AM Page 8-7

8-8

TABLE METHODThe table method applies the same principles as thecomputational and graph methods. The informationand limitations are contained in tables provided by themanufacturer. Figure 8-7 is an example of a table and aweight and balance calculation based on that table. Inthis problem, the total weight of 2,799 pounds andmoment of 2,278/100 are within the limits of the table.

Figure 8-7. Loading schedule placard.

COMPUTATIONS WITH A NEGATIVE ARMFigure 8-8 is a sample of weight and balance computa-tion using an airplane with a negative arm. It is importantto remember that a positive times a negative equals anegative, and a negative would be subtracted from thetotal moments.

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CH 08.qxd 10/24/03 7:07 AM Page 8-8

8-9

COMPUTATIONS WITH ZERO FUEL WEIGHTFigure 8-9 is a sample of weight and balance computa-tion using an airplane with a zero fuel weight. In thisexample, the total weight of the airplane less fuel is4,240 pounds, which is under the zero fuel weight of4,400 pounds. If the total weight of the airplanewithout fuel had exceeded 4,400 pounds, passengersor cargo would have to be reduced to bring theweight at or below the max zero fuel weight.

SHIFTING, ADDING, AND REMOVINGWEIGHTA pilot must be able to accurately and rapidly solve anyproblems that involve the shift, addition, or removal of

weight. For example, the pilot may load the aircraftwithin the allowable takeoff weight limit, then find aCG limit has been exceeded. The most satisfactorysolution to this problem is to shift baggage, passen-gers, or both. The pilot should be able to determine theminimum load shift needed to make the aircraft safefor flight. Pilots should be able to determine if shiftinga load to a new location will correct an out-of-limitcondition. There are some standardized calculationsthat can help make these determinations.

WEIGHT SHIFTINGWhen weight is shifted from one location to another,the total weight of the aircraft is unchanged. The totalmoments, however, do change in relation and propor-tion to the direction and distance the weight is moved.When weight is moved forward, the total momentsdecrease; when weight is moved aft, total momentsincrease. The moment change is proportional to theamount of weight moved. Since many aircraft haveforward and aft baggage compartments, weight maybe shifted from one to the other to change the CG. Ifstarting with a known aircraft weight, CG, and totalmoments, calculate the new CG (after the weight shift)by dividing the new total moments by the total aircraftweight.

To determine the new total moments, find out howmany moments are gained or lost when the weight isshifted. Assume that 100 pounds has been shifted fromstation 30 to station 150. This movement increases thetotal moments of the aircraft by 12,000 lb-in.

Moment when

at station 150 = 100 lb x 150 in = 15,000 lb-in

Moment when

at station 30 = 100 lb x 30 in = 3,000 lb-in

Moment change = 12,000 lb-in

By adding the moment change to the original moment(or subtracting if the weight has been moved forwardinstead of aft), the new total moments are obtained.Then determine the new CG by dividing the newmoments by the total weight:

Total moments = 616,000 + 12,000 = 628,000

CG = 628,000 = 78.5 in8,000 (Total weight)

The shift has caused the CG to shift to station 78.5

A simpler solution may be obtained by using a com-puter or calculator and a proportional formula. Thiscan be done because the CG will shift a distance that isproportional to the distance the weight is shifted.

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CH 08.qxd 10/24/03 7:07 AM Page 8-9

8-10

EXAMPLE

Weight Shifted = ∆CG (change of CG)_ _Total Weight Distance weight is shifted

100 = ∆CG8,000 120

∆CG = 1.5 in

The change of CG is added to (or subtracted from whenappropriate) the original CG to determine the new CG:

77 + 1.5 = 78.5 inches aft of datum

The shifting weight proportion formula can also beused to determine how much weight must be shifted toachieve a particular shift of the CG. The followingproblem illustrates a solution of this type.

EXAMPLE

Given:

Aircraft Total Weight . . . . . . . . . . . . . . . . .7,800 lb

CG . . . . . . . . . . . . . . . . . . . . . . . . . . . .Station 81.5

Aft CG Limit . . . . . . . . . . . . . . . . . . . . . . . . . .80.5

Determine how much cargo must be shifted from theaft cargo compartment at station 150 to the forwardcargo compartment at station 30 to move the CG toexactly the aft limit.

Solution:

Weight to be Shifted = ∆CG Total Weight Distance weight is shifted

Weight to be Shifted = 1.0 in7,800 120 in

Weight to be Shifted = 65 lb

WEIGHT ADDITION OR REMOVALIn many instances, the weight and balance of the air-craft will be changed by the addition or removal ofweight. When this happens, a new CG must be calculatedand checked against the limitations to see if the locationis acceptable. This type of weight and balance prob-lem is commonly encountered when the aircraft burnsfuel in flight, thereby reducing the weight located atthe fuel tanks. Most small aircraft are designed withthe fuel tanks positioned close to the CG; therefore,the consumption of fuel does not affect the CG to anygreat extent.

The addition or removal of cargo presents a CG changeproblem that must be calculated before flight. Theproblem may always be solved by calculations involv-ing total moments. A typical problem may involve thecalculation of a new CG for an aircraft which, whenloaded and ready for flight, receives some additionalcargo or passengers just before departure time.

EXAMPLE

Given:

Aircraft Total Weight . . . . . . . . . . . . . . . . .6,860 lb

CG Station . . . . . . . . . . . . . . . . . . . . . . . . . . . .80.0

Determine the location of the CG if 140 pounds of bag-gage is added to station 150.

Solution:

Added Weight = ∆CG New Total Weight Distance between weight

and old CG

140 = ∆CG 6,860 + 140 150–80

140 = ∆CG 7,000 70

CG = 1.4 in aft

Add ∆CG to old CGNew CG = 80.0 in + 1.4 in = 81.4 in

EXAMPLE

Given:

Aircraft Total Weight . . . . . . . . . . . . . . . . .6,100 lb

CG Station . . . . . . . . . . . . . . . . . . . . . . . . . . . .80.0

Determine the location of the CG if 100 pounds isremoved from station 150.

Solution:

Weight Removed = ∆CG New Total Weight Distance between

weight and old CG

100 = ∆CG 6,100 – 100 150 – 80

100 = ∆CG 6,000 70

CG = 1.2 in forward

Subtract ∆CG from old CGNew CG = 80 in - 1.2 in = 78.8 in

In the previous examples, the ∆CG is either added orsubtracted from the old CG. Deciding which toaccomplish is best handled by mentally calculatingwhich way the CG will shift for the particular weightchange. If the CG is shifting aft, the ∆CG is added tothe old CG; if the CG is shifting forward, the ∆CG issubtracted from the old CG.

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9-1

This chapter discusses the factors that affect airplaneperformance, which includes the airplane weight,atmospheric conditions, runway environment, and thefundamental physical laws governing the forces actingon an airplane.

IMPORTANCE OFPERFORMANCE DATAThe performance or operational information section ofthe Airplane Flight Manual/Pilot’s OperatingHandbook (AFM/POH) contains the operating data forthe airplane; that is, the data pertaining to takeoff,climb, range, endurance, descent, and landing. The useof this data in flying operations is mandatory for safeand efficient operation. Considerable knowledge andfamiliarity of the airplane can be gained through studyof this material.

It must be emphasized that the manufacturers’information and data furnished in the AFM/POH isnot standardized. Some provide the data in tabularform, while others use graphs. In addition, the per-formance data may be presented on the basis ofstandard atmospheric conditions, pressure altitude,or density altitude. The performance information inthe AFM/POH has little or no value unless the userrecognizes those variations and makes the necessaryadjustments.

To be able to make practical use of the airplane’s capa-bilities and limitations, it is essential to understand thesignificance of the operational data. The pilot must becognizant of the basis for the performance data, as wellas the meanings of the various terms used in expressingperformance capabilities and limitations.

Since the characteristics of the atmosphere have a pre-dominant effect on performance, it is necessary toreview some of the dominant factors—pressure andtemperature.

STRUCTURE OF THE ATMOSPHEREThe atmosphere is an envelope of air that surrounds theearth and rests upon its surface. It is as much a part ofthe earth as the seas or the land. However, air differsfrom land and water inasmuch as it is a mixture ofgases. It has mass, weight, and indefinite shape.

Air, like any other fluid, is able to flow and change itsshape when subjected to even minute pressures becauseof the lack of strong molecular cohesion. For example,gas will completely fill any container into which it isplaced, expanding or contracting to adjust its shape tothe limits of the container.

The atmosphere is composed of 78 percent nitrogen, 21percent oxygen, and 1 percent other gases, such asargon or helium. Most of the oxygen is containedbelow 35,000 feet altitude.

ATMOSPHERIC PRESSUREThough there are various kinds of pressure, pilots aremainly concerned with atmospheric pressure. It is oneof the basic factors in weather changes, helps to lift theairplane, and actuates some of the important flightinstruments in the airplane. These instruments are thealtimeter, the airspeed indicator, the rate-of-climb indi-cator, and the manifold pressure gauge.

Though air is very light, it has mass and is affectedby the attraction of gravity. Therefore, like any other

Ch 09.qxd 10/24/03 7:23 AM Page 9-1

9-2

substance, it has weight, and because of its weight, ithas force. Since it is a fluid substance, this force isexerted equally in all directions, and its effect onbodies within the air is called pressure. Under stan-dard conditions at sea level, the average pressureexerted by the weight of the atmosphere is approxi-mately 14.7 lb./in. The density of air has significanteffects on the airplane’s performance. As airbecomes less dense, it reduces:

• power because the engine takes in less air,

• thrust because the propeller is less efficient inthin air, and

• lift because the thin air exerts less force on theairfoils.

The pressure of the atmosphere varies with time andlocation. Due to the changing atmospheric pressure, astandard reference was developed. The standard atmos-phere at sea level is a surface temperature of 59°F or15°C and a surface pressure of 29.92 in. Hg or 1013.2millibars. [Figure 9-1]

A standard temperature lapse rate is one in which thetemperature decreases at the rate of approximately3.5°F or 2°C per thousand feet up to 36,000 feet. Abovethis point, the temperature is considered constant up to80,000 feet. A standard pressure lapse rate is one inwhich pressure decreases at a rate of approximately 1in. Hg per 1,000 feet of altitude gain to 10,000 feet.[Figure 9-2] The International Civil AviationOrganization (ICAO) has established this as a world-wide standard, and it is often referred to as

International Standard Atmosphere (ISA) or ICAOStandard Atmosphere. Any temperature or pressure thatdiffers from the standard lapse rates is considered non-standard temperature and pressure. Adjustments fornonstandard temperatures and pressures are providedon the manufacturer’s performance charts.

Since all airplane performance is compared and evalu-ated with respect to the standard atmosphere, all air-craft instruments are calibrated for the standardatmosphere. Thus, certain corrections must apply to theinstrumentation, as well as the airplane performance, ifthe actual operating conditions do not fit the standardatmosphere. In order to account properly for the non-standard atmosphere, certain related terms must bedefined.

PRESSURE ALTITUDEPressure altitude is the height above a standard datumplane. The airplane altimeter is essentially a sensitivebarometer calibrated to indicate altitude in the standardatmosphere. If the altimeter is set for 29.92 in. HgStandard Datum Plane (SDP), the altitude indicated isthe pressure altitude—the altitude in the standardatmosphere corresponding to the sensed pressure.

The SDP is a theoretical level where the weight of theatmosphere is 29.92 in. Hg as measured by a barometer.As atmospheric pressure changes, the SDP may be below,at, or above sea level. Pressure altitude is important as a

StandardSea LevelPressure

AtmosphericPressure

Inch

es o

f Mer

cury

29.92 30

25

20

15

10

5

0

Figure 9-1. Standard sea level pressure.

01,0002,0003,0004,0005,0006,0007,0008,0009,000

10,00011,00012,00013,00014,00015,00016,00017,00018,00019,00020,000

29.9228.8627.8226.8225.8424.8923.9823.0922.2221.3820.5719.7919.0218.2917.5716.8816.2115.5614.9414.3313.74

15.013.011.0

9.17.15.13.11.1

-0.9-2.8-4.8-6.8-8.8

-10.8-12.7-14.7-16.7-18.7-20.7-22.6-24.6

59.055.451.948.344.741.237.634.030.526.923.319.816.212.6

9.15.51.9

-1.6-5.2-8.8

-12.3

Altitude(ft)

Pressure(in. Hg)

Temp.(°C)

Temp.(°F)

Standard Atmosphere

Figure 9-2. Properties of standard atmosphere.

International Standard Atmosphere (ISA)—Also known as a standardday. A representative model of atmospheric air pressure, temperature,and density at various altitudes for reference purposes. At sea level, theISA has a temperature of 59°F or 15°C and a pressure of 29.92 in. Hgor 1013.2 millibars.

Pressure Altitude—The height above a standard datum plane.

Ch 09.qxd 10/24/03 7:23 AM Page 9-2

9-3

basis for determining airplane performance as well as forassigning flight levels to airplanes operating at above18,000 feet.

The pressure altitude can be determined by either oftwo methods:

1. by setting the barometric scale of the altimeter to29.92 and reading the indicated altitude, or

2. by applying a correction factor to the indicated alti-tude according to the reported “altimeter setting.”

DENSITY ALTITUDEThe more appropriate term for correlating aerodynamic per-formance in the nonstandard atmosphere is density altitude—the altitude in the standard atmosphere corresponding to aparticular value of air density.

Density altitude is pressure altitude corrected for non-standard temperature. As the density of the air increases(lower density altitude), airplane performance increasesand conversely as air density decreases (higher densityaltitude), airplane performance decreases. A decrease inair density means a high density altitude; and anincrease in air density means a lower density altitude.Density altitude is used in calculating airplane perform-ance. Under standard atmospheric condition, air at eachlevel in the atmosphere has a specific density, and understandard conditions, pressure altitude and density altitudeidentify the same level. Density altitude, then, is the ver-tical distance above sea level in the standard atmosphereat which a given density is to be found.

The computation of density altitude must involveconsideration of pressure (pressure altitude) andtemperature. Since airplane performance data atany level is based upon air density under standardday conditions, such performance data apply to airdensity levels that may not be identical with altime-ter indications. Under conditions higher or lowerthan standard, these levels cannot be determineddirectly from the altimeter.

Density altitude is determined by first finding pressurealtitude, and then correcting this altitude for nonstan-dard temperature variations. Since density variesdirectly with pressure, and inversely with temperature,a given pressure altitude may exist for a wide range oftemperature by allowing the density to vary. However,a known density occurs for any one temperature andpressure altitude. The density of the air, of course, has apronounced effect on airplane and engine performance.Regardless of the actual altitude at which the airplaneis operating, it will perform as though it were operatingat an altitude equal to the existing density altitude.

For example, when set at 29.92, the altimeter may indi-cate a pressure altitude of 5,000 feet. According to the

AFM/POH, the ground run on takeoff may require a dis-tance of 790 feet under standard temperature conditions.However, if the temperature is 20°C above standard, theexpansion of air raises the density level. Using tempera-ture correction data from tables or graphs, or by derivingthe density altitude with a computer, it may be found thatthe density level is above 7,000 feet, and the ground runmay be closer to 1,000 feet.

Air density is affected by changes in altitude, temper-ature, and humidity. High density altitude refers tothin air while low density altitude refers to dense air.The conditions that result in a high density altitudeare high elevations, low atmospheric pressures, hightemperatures, high humidity, or some combination ofthese factors. Lower elevations, high atmosphericpressure, low temperatures, and low humidity aremore indicative of low density altitude.

Using a flight computer, density altitude can be com-puted by inputting the pressure altitude and outside airtemperature at flight level. Density altitude can also bedetermined by referring to the table and chart in figures9-3 and 9-4.

Method for DeterminingPressure Altitude

Alternate Method for DeterminingPressure Altitude

If AltimeterSetting is:

AltitudeCorrection

28.028.128.228.328.428.528.628.728.828.929.029.129.229.329.429.529.629.729.829.929.9230.030.130.230.330.430.530.630.730.830.931.0

1,8251,7251,6301,5351,4351,3401,2451,1501,050

955865770675580485390300205110

200

-75-165-255-350-440-530-620-710-805-895-965

To GetPressure Altitude

Set 29.92 in pressurewindow of altimeter andread altitude. This ispressure altitude.

Add To FieldElevation

Subtract From FieldElevation

Pressure Altitude

Figure 9-3. Field elevation versus pressure altitude.Density Altitude—Pressure altitude corrected for nonstandard tempera-ture.

Ch 09.qxd 10/24/03 7:23 AM Page 9-3

9-4

EFFECTS OF PRESSURE ON DENSITYSince air is a gas, it can be compressed or expanded.When air is compressed, a greater amount of air canoccupy a given volume. Conversely, when pressure ona given volume of air is decreased, the air expands andoccupies a greater space. That is, the original columnof air at a lower pressure contains a smaller mass of air.In other words, the density is decreased. In fact, densityis directly proportional to pressure. If the pressure isdoubled, the density is doubled, and if the pressure islowered, so is the density. This statement is true only ata constant temperature.

EFFECT OF TEMPERATURE ON DENSITYIncreasing the temperature of a substance decreases itsdensity. Conversely, decreasing the temperature

increases the density. Thus, the density of air variesinversely with temperature. This statement is true onlyat a constant pressure.

In the atmosphere, both temperature and pressuredecrease with altitude, and have conflicting effectsupon density. However, the fairly rapid drop in pres-sure as altitude is increased usually has the dominatingeffect. Hence, pilots can expect the density to decreasewith altitude.

EFFECT OF HUMIDITY (MOISTURE) ONDENSITYThe preceding paragraphs have assumed that the airwas perfectly dry. In reality, it is never completely dry.The small amount of water vapor suspended in theatmosphere may be almost negligible under certainconditions, but in other conditions humidity maybecome an important factor in the performance of anairplane. Water vapor is lighter than air; consequently,moist air is lighter than dry air. Therefore, as the watercontent of the air increases, the air becomes less dense,increasing density altitude and decreasing perform-ance. It is lightest or least dense when, in a given set ofconditions, it contains the maximum amount of watervapor.

Humidity, also called “relative humidity,” refers to theamount of water vapor contained in the atmosphere,and is expressed as a percentage of the maximumamount of water vapor the air can hold. This amountvaries with the temperature; warm air can hold morewater vapor, while colder air can hold less. Perfectlydry air that contains no water vapor has a relativehumidity of 0 percent, while saturated air, that cannothold any more water vapor, has a relative humidity of100 percent. Humidity alone is usually not consideredan important factor in calculating density altitude andairplane performance; however, it does contribute.

The higher the temperature, the greater amount of watervapor that the air can hold. When comparing two separateair masses, the first warm and moist (both qualities tendingto lighten the air) and the second cold and dry (both quali-ties making it heavier), the first necessarily must be lessdense than the second. Pressure, temperature, and humidityhave a great influence on airplane performance because oftheir effect upon density. There are no rules-of-thumb orcharts used to compute the effects of humidity on densityaltitude, so take this into consideration by expecting adecrease in overall performance in high humidityconditions.

PERFORMANCE“Performance” is a term used to describe the ability ofan airplane to accomplish certain things that make it

Figure 9-4. Density altitude chart.

15,000

14,000

13,00014

,000

13,00

0

12,000

12,00

0

11,000

11,00

0

10,000

10,00

0

9,000

9,000

P

RESSURE ALTITU

DE – FE

ET

8,000

7,000

6,000

5,000

8,000

7,000

6,000

5,000

4,000

4,000

3,000

3,000

2,000

2,000

1,000

1,000

S.L.

-1,00

0

SEA LEVEL

-2,00

0

5040302010 °C0-10-20

0 10 20 30 40 50 60 70 80 90 100 110 120°F

Outside Air Temperature

Den

sity

Alt

itu

de

– F

eet

STANDAR

D TEM

PERATU

RE

Relative Humidity—The amount of water vapor contained in the aircompared to the amount the air could hold.

Ch 09.qxd 10/24/03 7:23 AM Page 9-4

9-5

useful for certain purposes. For example, the ability ofthe airplane to land and take off in a very short distanceis an important factor to the pilot who operates in andout of short, unimproved airfields. The ability to carryheavy loads, fly at high altitudes at fast speeds, or travellong distances is essential performance for operators ofairline and executive type airplanes.

The chief elements of performance are the takeoff andlanding distance, rate of climb, ceiling, payload, range,speed, maneuverability, stability, and fuel economy.Some of these factors are often directly opposed: forexample, high speed versus shortness of landing dis-tance; long range versus great payload; and high rate ofclimb versus fuel economy. It is the preeminence of oneor more of these factors which dictates differencesbetween airplanes and which explains the high degreeof specialization found in modern airplanes.

The various items of airplane performance result from thecombination of airplane and powerplant characteristics.The aerodynamic characteristics of the airplane generallydefine the power and thrust requirements at various condi-tions of flight while powerplant characteristics generallydefine the power and thrust available at various conditionsof flight. The matching of the aerodynamic configurationwith the powerplant is accomplished by the manufacturerto provide maximum performance at the specific designcondition; e.g., range, endurance, and climb.

STRAIGHT-AND-LEVEL FLIGHTAll of the principal items of flight performance involvesteady-state flight conditions and equilibrium of theairplane. For the airplane to remain in steady, levelflight, equilibrium must be obtained by a lift equal tothe airplane weight and a powerplant thrust equal to theairplane drag. Thus, the airplane drag defines the thrustrequired to maintain steady, level flight.

All parts of the airplane that are exposed to the air con-tribute to the drag, though only the wings provide liftof any significance. For this reason, and certain othersrelated to it, the total drag may be divided into twoparts: the wing drag (induced) and the drag of every-thing but the wings (parasite).

The total power required for flight then can be consideredas the sum of induced and parasite effects; that is, the totaldrag of the airplane. Parasite drag is the sum of pressureand friction drag, which is due to the airplane’s basic con-figuration and, as defined, is independent of lift. Induceddrag is the undesirable but unavoidable consequence ofthe development of lift.

While the parasite drag predominates at high speed,induced drag predominates at low speed. [Figure 9-5]For example, if an airplane in a steady flight condi-tion at 100 knots is then accelerated to 200 knots, the

parasite drag becomes four times as great, but thepower required to overcome that drag is eight timesthe original value. Conversely, when the airplane isoperated in steady, level flight at twice as great aspeed, the induced drag is one-fourth the originalvalue, and the power required to overcome that dragis only one-half the original value.

The wing or induced drag changes with speed in a verydifferent way, because of the changes in the angle ofattack. Near the stalling speed, the wing is inclined tothe relative wind at nearly the stalling angle, and itsdrag is very strong. But at cruise flying speed, with theangle of attack nearly zero, induced drag is minimal.After attaining cruise speed, the angle of attack changesvery little with any further increase in speed, and thedrag of the wing increases in direct proportion to anyfurther increase in speed. This does not consider thefactor of compressibility drag that is involved at speedsbeyond 260 knots.

To sum up these changes, as the speed increases fromstalling speed to VNE, the induced drag decreases andparasite drag increases.

When the airplane is in steady, level flight, the condi-tion of equilibrium must prevail. The unacceleratedcondition of flight is achieved with the airplanetrimmed for lift equal to weight and the powerplant setfor a thrust to equal the airplane drag.

The maximum level flight speed for the airplane willbe obtained when the power or thrust required equalsthe maximum power or thrust available from the

Speed—Knots

Dra

g—P

ound

s

Parasite Drag

Induced Drag

Total Drag

Stall

Figure 9-5. Drag versus speed.

Ch 09.qxd 10/24/03 7:23 AM Page 9-5

9-6

powerplant. [Figure 9-6] The minimum level flightairspeed is not usually defined by thrust or powerrequirement since conditions of stall or stability andcontrol problems generally predominate.

CLIMB PERFORMANCEClimb depends upon the reserve power or thrust.Reserve power is the available power over and abovethat required to maintain horizontal flight at a givenspeed. Thus, if an airplane is equipped with an enginethat produces 200 total available horsepower and theairplane requires only 130 horsepower at a certain levelflight speed, the power available for climb is 70 horse-power.

Although the terms “power” and “thrust” are some-times used interchangeably, erroneously implying thatthey are synonymous, it is important to distinguishbetween the two when discussing climb performance.Work is the product of a force moving through adistance and is usually independent of time. Work ismeasured by several standards; the most common unitis called a “foot-pound.” If a 1-pound mass is raised 1foot, a work unit of 1 foot-pound has been performed.The common unit of mechanical power is horse-power; one horsepower is work equivalent to lifting33,000 pounds a vertical distance of 1 foot in 1minute. The term “power” implies work rate or unitsof work per unit of time, and as such is a function ofthe speed at which the force is developed. “Thrust,”also a function of work, means the force that impartsa change in the velocity of a mass. This force is meas-ured in pounds but has no element of time or rate. Itcan be said then, that during a steady climb, the rateof climb is a function of excess thrust.

When the airplane is in steady, level flight or with aslight angle of climb, the vertical component of lift isvery nearly the same as the actual total lift. Such climb-ing flight would exist with the lift very nearly equal tothe weight. The net thrust of the powerplant may beinclined relative to the flightpath, but this effect will beneglected here for the sake of simplicity. Although theweight of the airplane acts vertically, a component ofweight will act rearward along the flightpath. [Figure9-7]

If it is assumed that the airplane is in a steady climbwith essentially a small inclination of the flightpath,the summation of forces along the flightpath resolvesto the following:

Forces forward = Forces aft

The basic relationship neglects some of the factorsthat may be of importance for airplanes of very highclimb performance. (For example, a more detailedconsideration would account for the inclination ofthrust from the flightpath, lift not being equal toweight, and a subsequent change of induced drag.)However, this basic relationship will define theprincipal factors affecting climb performance.

This relationship means that, for a given weight of theairplane, the angle of climb depends on the differencebetween thrust and drag, or the excess thrust. [Figure9-8] Of course, when the excess thrust is zero, the incli-nation of the flightpath is zero, and the airplane will bein steady, level flight. When the thrust is greater thanthe drag, the excess thrust will allow a climb angledepending on the value of excess thrust. On the otherhand, when the thrust is less than the drag, the defi-ciency of thrust will allow an angle of descent.

The most immediate interest in the climb angleperformance involves obstacle clearance. Themost obvious purpose for which it might be used

Speed—Knots

Pow

er R

equi

red—

HP

MaximumAvailable Power

High CruiseSpeed

Low CruiseSpeedMin.

Speed

MaximumLevelFlightSpeed

Figure 9-6. Power versus speed.

Power—Work rate or units of work per unit of time, and is a function ofthe speed at which the force is developed.

Thrust—Also a function of work and means the force that imparts achange in the velocity of a mass.

Work—The product of a force moving through a distance and is usuallyexpressed in foot-pounds.

Flight Path

Thrust

Drag

Weight

ClimbAngle

γ

γ

γ

Velocity

Rate ofClimbRC

W SIN γComponent ofWeight AlongFlight Path

Lift

Figure 9-7. Weight has rearward component.

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is to clear obstacles when climbing out of short orconfined airports.

The maximum angle of climb would occur where thereexists the greatest difference between thrust availableand thrust required; i.e., for the propeller-powered air-plane, the maximum excess thrust and angle of climbwill occur at some speed just above the stall speed.Thus, if it is necessary to clear an obstacle after takeoff,the propeller-powered airplane will attain maximumangle of climb at an airspeed close to—if not at—thetakeoff speed.

Of greater interest in climb performance are the factorsthat affect the rate of climb. The vertical velocity of anairplane depends on the flight speed and the inclinationof the flightpath. In fact, the rate of climb is the verticalcomponent of the flightpath velocity.

For rate of climb, the maximum rate would occurwhere there exists the greatest difference betweenpower available and power required. [Figure 9-9] Theabove relationship means that, for a given weight of the

airplane, the rate of climb depends on the differencebetween the power available and the power required, orthe excess power. Of course, when the excess power iszero, the rate of climb is zero and the airplane is insteady, level flight. When power available is greaterthan the power required, the excess power will allow arate of climb specific to the magnitude of excess power.

During a steady climb, the rate of climb will depend onexcess power while the angle of climb is a function ofexcess thrust.

The climb performance of an airplane is affected bycertain variables. The conditions of the airplane’smaximum climb angle or maximum climb rateoccur at specific speeds, and variations in speedwill produce variations in climb performance.There is sufficient latitude in most airplanes thatsmall variations in speed from the optimum do notproduce large changes in climb performance, andcertain operational considerations may requirespeeds slightly different from the optimum. Ofcourse, climb performance would be most criticalwith high gross weight, at high altitude, inobstructed takeoff areas, or during malfunction of apowerplant. Then, optimum climb speeds are nec-essary.

Weight has a very pronounced effect on airplane per-formance. If weight is added to the airplane, it must flyat a higher angle of attack to maintain a given altitudeand speed. This increases the induced drag of thewings, as well as the parasite drag of the airplane.Increased drag means that additional thrust is needed toovercome it, which in turn means that less reservethrust is available for climbing. Airplane designers goto great effort to minimize the weight since it has sucha marked effect on the factors pertaining to perform-ance.

A change in the airplane’s weight produces a twofoldeffect on climb performance. First, a change in weightwill change the drag and the power required. This altersthe reserve power available, which in turn, affects boththe climb angle and the climb rate. Secondly, anincrease in weight will reduce the maximum rate ofclimb, but the airplane must be operated at a higherclimb speed to achieve the smaller peak climb rate.

An increase in altitude also will increase the powerrequired and decrease the power available. Therefore,the climb performance of an airplane diminishes withaltitude. The speeds for maximum rate of climb, maxi-mum angle of climb, and maximum and minimumlevel flight airspeeds vary with altitude. As altitude isincreased, these various speeds finally converge at theabsolute ceiling of the airplane. At the absolute ceiling,there is no excess of power and only one speed will

Thrust Available

ThrustRequiredor Drag

Stall

ReserveThrust

Speedfor Max.Angle ofClimb

Speed—Knots

Thr

ust A

vaila

ble

and

Thr

ust R

equi

red—

Lbs.

Figure 9-8.Thrust versus climb angle.

Reserve Power

Speed—Knots

Pow

er A

vaila

ble

and

Pow

er R

equi

red—

HP.

Power Required

Power Available

Speed for Maximum Rate of Climb

Figure 9-9. Power versus climb rate.

Ch 09.qxd 10/24/03 7:23 AM Page 9-7

allow steady, level flight. Consequently, the absoluteceiling of the airplane produces zero rate of climb. Theservice ceiling is the altitude at which the airplane isunable to climb at a rate greater than 100 feet perminute. Usually, these specific performance referencepoints are provided for the airplane at a specific designconfiguration. [Figure 9-10]

In discussing performance, it frequently is convenientto use the terms “power loading” and “wing loading.”Power loading is expressed in pounds per horsepowerand is obtained by dividing the total weight of the air-plane by the rated horsepower of the engine. It is a sig-nificant factor in the airplane’s takeoff and climbcapabilities. Wing loading is expressed in pounds persquare foot and is obtained by dividing the total weightof the airplane in pounds by the wing area (includingailerons) in square feet. It is the airplane’s wing loadingthat determines the landing speed. These factors arediscussed in subsequent sections of this chapter.

RANGE PERFORMANCEThe ability of an airplane to convert fuel energy intoflying distance is one of the most important items ofairplane performance. In flying operations, the prob-lem of efficient range operation of an airplane appearsin two general forms:

1. to extract the maximum flying distance from agiven fuel load or,

2. to fly a specified distance with a minimumexpenditure of fuel.

A common denominator for each of these operatingproblems is the “specific range”; that is, nautical miles

of flying distance per pound of fuel. Cruise flightoperations for maximum range should be conductedso that the airplane obtains maximum specific rangethroughout the flight.

The specific range can be defined by the followingrelationship:

nautical milesspecific range = —————————-

lb. of fuel

or,

nautical miles/hr.specific range = ——————————-

lb. of fuel/hr.

or,

knotsspecific range = —————-

fuel flow

If maximum specific range is desired, the flight condi-tion must provide a maximum of speed per fuel flow.

Range must be clearly distinguished from the item ofendurance. [Figure 9-11] The item of range involvesconsideration of flying distance, while enduranceinvolves consideration of flying time. Thus, it is appro-priate to define a separate term, “specific endurance.”

flight hoursspecific endurance = ———————-

lb. of fuel

or,flight hours/hr.

specific endurance = —————————lb. of fuel/hr.

or,

1specific endurance = —————-

fuel flow

If maximum endurance is desired, the flight conditionmust provide a minimum of fuel flow. While the peakvalue of specific range would provide maximum rangeoperation, long-range cruise operation is generally rec-ommended at some slightly higher airspeed. Mostlong-range cruise operations are conducted at the flightcondition that provides 99 percent of the absolute max-imum specific range. The advantage of such operationis that 1 percent of range is traded for 3 to 5 percenthigher cruise speed. Since the higher cruise speed has agreat number of advantages, the small sacrifice of

9-8

Absolute Ceiling

Service Ceiling

Figure 9-10. Absolute and service ceiling.

Ch 09.qxd 10/24/03 7:23 AM Page 9-8

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range is a fair bargain. The values of specific range ver-sus speed are affected by three principal variables:

1. airplane gross weight,

2. altitude, and

3. the external aerodynamic configuration of the air-plane. These are the source of range andendurance operating data included in the per-formance section of the AFM/POH.

“Cruise control” of an airplane implies that the airplaneis operated to maintain the recommended long-rangecruise condition throughout the flight. Since fuel isconsumed during cruise, the gross weight of the air-plane will vary and optimum airspeed, altitude, andpower setting can also vary. “Cruise control” means thecontrol of the optimum airspeed, altitude, and powersetting to maintain the 99 percent maximum specificrange condition. At the beginning of cruise flight, therelatively high initial weight of the airplane will requirespecific values of airspeed, altitude, and power settingto produce the recommended cruise condition. As fuelis consumed and the airplane’s gross weight decreases,the optimum airspeed and power setting may decrease,or, the optimum altitude may increase. In addition, theoptimum specific range will increase. Therefore, thepilot must provide the proper cruise control procedureto ensure that optimum conditions are maintained.

Total range is dependent on both fuel availableand specific range. When range and economy ofoperation are the principal goals, the pilot mustensure that the airplane will be operated at therecommended long- range cruise condition. Bythis procedure, the airplane will be capable of itsmaximum design-operating radius, or canachieve flight distances less than the maximumwith a maximum of fuel reserve at the destina-tion.

The propeller-driven airplane combines the propeller withthe reciprocating engine for propulsive power. In the caseof the reciprocating engine, fuel flow is determinedmainly by the shaft power put into the propeller ratherthan thrust. Thus, the fuel flow can be related directly tothe power required to maintain the airplane in steady, levelflight. This fact allows for the determination of rangethrough analysis of power required versus speed.

The maximum endurance condition would be obtainedat the point of minimum power required since thiswould require the lowest fuel flow to keep the airplanein steady, level flight. Maximum range condition wouldoccur where the proportion between speed and powerrequired is greatest. [Figure 9-11]

The maximum range condition is obtained at maximumlift/drag ratio (L/D max), and it is important to note that

for a given airplane configuration, the maximumlift/drag ratio occurs at a particular angle of attack andlift coefficient, and is unaffected by weight or altitude.A variation in weight will alter the values of airspeedand power required to obtained the maximum lift/dragratio. [Figure 9-12]

The variations of speed and power required mustbe monitored by the pilot as part of the cruisecontrol procedure to maintain the maximumlift/drag ratio. When the airplane’s fuel weight isa small part of the gross weight and the airplane’srange is small, the cruise control procedure canbe simplified to essentially maintaining a con-stant speed and power setting throughout thetime of cruise flight. The long-range airplane hasa fuel weight that is a considerable part of thegross weight, and cruise control procedures mustemploy scheduled airspeed and power changes tomaintain optimum range conditions.

Speed—Knots

Pow

er R

equi

red—

HP

MaximumRange at(L/D) MAX

MaximumEnduranceat Min. PowerRequired

Applicable fora Particular– Weight– Altitude– Configuration

Figure 9-11. Airspeeds for maximum endurance vs. maximumrange.

Speed—Knots

Pow

er R

equi

red—

HP L/D MAX

Higher Wt.

Basic Wt.

Lower Wt.

ConstantAltitude

Figure 9-12. Effect of weight on speed for maximum range.

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The effect of altitude on the range of the propeller-driven airplane may be understood by inspection offigure 9-13. A flight conducted at high altitude willhave a greater true airspeed, and the power requiredwill be proportionately greater than when conductedat sea level. The drag of the airplane at altitude is thesame as the drag at sea level, but the higher trueairspeed causes a proportionately greater powerrequired. Note that the straight line that is tangentto the sea level power curve is also tangent to thealtitude power curve.

The effect of altitude on specific range also can beappreciated from the previous relationships. If a changein altitude causes identical changes in speed and powerrequired, the proportion of speed to power requiredwould be unchanged. The fact implies that the specificrange of the propeller-driven airplane would be unaf-fected by altitude. Actually, this is true to the extent thatspecific fuel consumption and propeller efficiency arethe principal factors that could cause a variation of spe-cific range with altitude. If compressibility effects arenegligible, any variation of specific range with altitudeis strictly a function of engine/propeller performance.

The airplane equipped with the reciprocating enginewill experience very little, if any, variation of specificrange up to its absolute altitude. There is negligiblevariation of brake specific fuel consumption for val-ues of brake horsepower below the maximum cruisepower rating of the engine that is the lean range ofengine operation. Thus, an increase in altitude willproduce a decrease in specific range only when theincreased power requirement exceeds the maximumcruise power rating of the engine. One advantage ofsupercharging is that the cruise power may be main-tained at high altitude, and the airplane may achievethe range at high altitude with the correspondingincrease in true airspeed. The principal differences in

the high altitude cruise and low altitude cruise are thetrue airspeeds and climb fuel requirements.

GROUND EFFECTGround effect is due to the interference of thesurface with the flow pattern about the airplanein flight. Ground effect can be detected andmeasured up to an altitude equal to one wingspan above the surface. However, ground effectis most significant when the airplane (especiallythe low-wing airplane) is maintaining a constantattitude at low airspeed and low altitude (forexample, during landing flare before touchdown,and during takeoff when the airplane lifts off andaccelerates to climb speed).

When the wing is under the influence of groundeffect, there is a reduction in upwash, downwash, andtip vortices. As a result of the reduced tip vortices,induced drag is reduced. When the wing is at a heightequal to one-fourth the span, the reduction in induceddrag is about 25 percent, and when the wing is at aheight equal to one-tenth the span, the reduction ininduced drag is about 50 percent. At high speedswhere parasite drag predominates, induced drag is asmall part of the total drag. Consequently, the effectsof ground effect are of greater concern during takeoffand landing. [Figure 9-14]

Assuming that the airplane descends into ground effectmaintaining a constant angle of attack and a constantairspeed, the following effects will take place:

Because of the reduction in drag, a smaller wingangle of attack will be required to produce the samelift coefficient or, if a constant wing angle of attackis maintained, the wing will experience an increasein lift coefficient.

As a result of the reduction in drag, the thrust requiredat low speeds will be reduced.

The reduction in downwash at the horizontal tail willreduce the effectiveness of the elevator. It may cause apitch-down tendency, thus requiring greater up elevatorto trim the airplane.

In the majority of cases, ground effect will cause anincrease in pressure at the static source and produce alower indication of airspeed and altitude.

During the landing flare when the airplane is broughtinto ground effect at a constant angle of attack, the air-plane will experience an increase in lift coefficient.

Speed—Knots

Pow

er R

equi

red—

HP

L/D MAX

ConstantWeight

Sea Level

At Altitude

Figure 9-13. Effect of altitude on range.

Brake Specific Fuel Consumption—The number of pounds of fuelburned per hour to produce one horsepower in a reciprocating engine.

Brake Horsepower—The power delivered at the propeller shaft (maindrive or main output) of an aircraft engine.

Ground Effect—A condition due to the interference of the surface withthe airflow around the wing and which can be detected up to an altitudeof one wing span above the surface.

Ch 09.qxd 10/24/03 8:59 AM Page 9-10

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Thus, a “floating” sensation may be experienced.Because of the reduced drag in ground effect, anyexcess speed at the point of landing flare may result ina considerable “float” distance. If a power approach isbeing made, the power setting should be reduced as theairplane descends into ground effect to avoid over-shooting the desired touchdown point.

During takeoff, the airplane leaving ground effectencounters the reverse of entering ground effect. Forexample, an airplane leaving ground effect will:

require an increase in angle of attack to maintain thesame lift coefficient,

Span

Height

ReducedTip

Vortex

AIRPLANE OUT OFGROUND EFFECT

Downwash

Tip Vortex

Upwash

Reduced Downwashand Upwash

AIRPLANE INGROUND EFFECT

CL Constant

60

50

40

30

20

10

0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

Ratio of Wing Height to Span

AIRPLANE INGROUND EFFECT

AIRPLANE OUT OFGROUND EFFECT

Perc

ent R

educt

ion in

Indu

ced D

rag C

oeffic

ient

Lift

Coeffic

ient

Th

rust

Re

qu

ire

d—

Lb

s.

AIRPLANE OUT OFGROUND EFFECT

Angle of Attack

AIRPLANE INGROUND EFFECT

Speed—Knots

Figure 9-14. Ground effect.

Ch 09.qxd 10/24/03 7:23 AM Page 9-11

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experience an increase in induced drag and thrustrequired,

experience a pitch-up tendency requiring less elevatortravel to trim the airplane because of the increase indownwash at the horizontal tail, and

usually experience a reduction in static source pressureand an increase in indicated airspeed.

Due to the reduced drag in ground effect, the airplanemay seem able to take off below the recommended air-speed. However, as the airplane rises out of groundeffect with an insufficient airspeed, initial climb per-formance may prove to be marginal because of theincreased drag. Under extreme conditions such as high-density altitude, high temperature, and maximum grossweight, the airplane may be able to become airborne atan insufficient airspeed, but unable to fly out of groundeffect. Consequently, the airplane may not be able toclear an obstruction, or may settle back on the runway.Under marginal conditions, it is important the airplanetakes off at the recommended speed that will provideadequate initial climb performance. If the runway islong enough, or no obstacles exist, ground effect can beused to an advantage by using the reduced drag toimprove initial acceleration. Ground effect is importantto normal flight operations in the performance of softand rough field takeoffs and landings. The procedurefor takeoff from these surfaces is to transfer as muchweight as possible to the wings during the ground run,and to lift off with the aid of ground effect before trueflying speed is attained. It is then necessary to reducethe angle of attack gradually until normal airspeed isattained before attempting to climb away from theground effect.

REGION OF REVERSED COMMANDThe aerodynamic properties of the airplane generallydetermine the power requirements at various conditionsof flight, while the powerplant capabilities generallydetermine the power available at various conditions offlight. When the airplane is in steady, level flight, thecondition of equilibrium must prevail. An unacceleratedcondition of flight is achieved when lift equals weight,and the powerplant is set for a thrust equal to the airplanedrag. The power required to achieve equilibrium in con-stant-altitude flight at various airspeeds is depicted on apower required curve. The power required curve illus-trates the fact that at low airspeeds near the stall or mini-mum controllable airspeed, the power setting requiredfor steady, level flight is quite high.

Flight in the region of normal command means thatwhile holding a constant altitude, a higher airspeedrequires a higher power setting and a lower airspeedrequires a lower power setting. The majority of all air-

plane flying (climb, cruise, and maneuvers) is con-ducted in the region of normal command.

Flight in the region of reversed command means thata higher airspeed requires a lower power setting and alower airspeed requires a higher power setting to holdaltitude. It does not imply that a decrease in power willproduce lower airspeed. The region of reversed com-mand is encountered in the low speed phases of flight.Flight speeds below the speed for maximum endurance(lowest point on the power curve) require higher powersettings with a decrease in airspeed. Since the need toincrease the required power setting with decreasedspeed is contrary to the normal command of flight, theregime of flight speeds between the speed for minimumrequired power setting and the stall speed (or minimumcontrol speed) is termed the region of reversed com-mand. In the region of reversed command, a decreasein airspeed must be accompanied by an increasedpower setting in order to maintain steady flight.

Figure 9-15 shows the “maximum power available” as acurved line. Lower power settings, such as cruise power,would also appear in a similar curve. The lowest pointon the power required curve represents the speed atwhich the lowest brake horsepower will sustain levelflight. This is termed the best endurance airspeed.

An airplane performing a low airspeed, high pitchattitude power approach for a short-field landing isan example of operating in the region of reversedcommand. If an unacceptably high sink rate shoulddevelop, it may be possible for the pilot to reduce orstop the descent by applying power. But without fur-ther use of power, the airplane would probably stallor be incapable of flaring for the landing. Merely

Region of Reversed Command—Means in flight a higher airspeedrequires a lower power setting and a lower airspeed requires a higherpower setting to maintain altitude.

Pow

er S

ettin

g

MaximumPower Available

ExcessPower

Power Require

d

Region ofReversedCommand

Best Endurance Speed

Airspeed

Figure 9-15. Power required curve.

Ch 09.qxd 10/24/03 7:23 AM Page 9-12

9-13

lowering the nose of the airplane to regain flyingspeed in this situation, without the use of power,would result in a rapid sink rate and correspondingloss of altitude.

If during a soft-field takeoff and climb, for example,the pilot attempts to climb out of ground effect withoutfirst attaining normal climb pitch attitude and airspeed,the airplane may inadvertently enter the region ofreversed command at a dangerously low altitude. Evenwith full power, the airplane may be incapable ofclimbing or even maintaining altitude. The pilot’s onlyrecourse in this situation is to lower the pitch attitude inorder to increase airspeed, which will inevitably resultin a loss of altitude.

Airplane pilots must give particular attention to precisecontrol of airspeed when operating in the low flightspeeds of the region of reversed command.

RUNWAY SURFACE AND GRADIENTRunway conditions affect takeoff and landing perform-ance. Typically, performance chart information assumespaved, level, smooth, and dry runway surfaces. Since notwo runways are alike, the runway surface differs fromone runway to another, as does the runway gradient orslope. [Figure 9-16]

Runway surfaces vary widely from one airport toanother. The runway surface encountered may be con-crete, asphalt, gravel, dirt, or grass. The runway surfacefor a specific airport is noted in the Airport/FacilityDirectory. Any surface that is not hard and smooth willincrease the ground roll during takeoff. This is due tothe inability of the tires to smoothly roll along the run-way. Tires can sink into soft, grassy, or muddy run-ways. Potholes or other ruts in the pavement can be thecause of poor tire movement along the runway.

Obstructions such as mud, snow, or standing waterreduce the airplane’s acceleration down the runway.Although muddy and wet surface conditions can reducefriction between the runway and the tires, they can alsoact as obstructions and reduce the landing distance.[Figure 9-17]

Braking effectiveness is another consideration whendealing with various runway types. The condition ofthe surface affects the braking ability of the airplane.

Figure 9-16. Charts assume paved, level, dry runway conditions.

Figure 9-17. Airplane performance depends greatly on therunway surface.

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The amount of power that is applied to the brakeswithout skidding the tires is referred to as brakingeffectiveness. Ensure that runways are adequate inlength for takeoff acceleration and landing decelera-tion when less than ideal surface conditions are beingreported.

The gradient or slope of the runway is the amount ofchange in runway height over the length of the runway.The gradient is expressed as a percentage such as a 3percent gradient. This means that for every 100 feet ofrunway length, the runway height changes by 3 feet. Apositive gradient indicates that the runway heightincreases, and a negative gradient indicates that therunway decreases in height. An upsloping runwayimpedes acceleration and results in a longer ground runduring takeoff. However, landing on an upsloping run-way typically reduces the landing roll. A downslopingrunway aids in acceleration on takeoff resulting inshorter takeoff distances. The opposite is true whenlanding, as landing on a downsloping runway increaseslanding distances. Runway slope information is con-tained in the Airport/Facility Directory. [Figure 9-18]

WATER ON THE RUNWAY AND DYNAMICHYDROPLANINGWater on the runways reduces the friction betweenthe tires and the ground, and can reduce brakingeffectiveness. The ability to brake can be completelylost when the tires are hydroplaning because a layerof water separates the tires from the runway surface.This is also true of braking effectiveness whenrunways are covered in ice.

When the runway is wet, the pilot may be confrontedwith dynamic hydroplaning. Dynamic hydroplaningis a condition in which the airplane tires ride on a thin

sheet of water rather than on the runway’s surface.Because hydroplaning wheels are not touching the runway,braking and directional control are almost nil.

To help minimize dynamic hydroplaning, somerunways are grooved to help drain off water; butmost runways are not.

Tire pressure is a factor in dynamic hydroplaning.By the simple formula in figure 9-19, the pilot cancalculate the minimum speed, in knots, at whichhydroplaning will begin. In plain language, the mini-mum hydroplaning speed is determined by multiplyingthe square root of the main gear tire pressure in poundsper square inch (p.s.i.), by nine. For example, if themain gear tire pressure is at 36 pounds per square inch,the airplane would begin hydroplaning at 54 knots.

Figure 9-18. A/FDs provide information regarding runway slope.

MINIMUM DYNAMICHYDROPLANING SPEED

(ROUNDED OFF) =

9 x

36 = 69 X 6 = 54 KNOTS

TIRE PRESSURE (IN PSI)

Figure 9-19. Dynamic hydroplane formula and example for atire pressure of 36 pounds.

Dynamic Hydroplaning—A condition in which the airplane tires ride ona thin sheet of water rather than the runway surface.

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Landing at higher than recommended touchdownspeeds will expose the airplane to a greater potentialfor hydroplaning. And once hydroplaning starts, it cancontinue well below the minimum, initial hydroplaningspeed.

On wet runways, directional control can be maximizedby landing into the wind. Abrupt control inputs shouldbe avoided. When the runway is wet, anticipate brakingproblems well before landing and be prepared forhydroplaning. Opt for a suitable runway most alignedwith the wind. Mechanical braking may be ineffective,so aerodynamic braking should be used to its fullestadvantage.

TAKEOFF AND LANDINGPERFORMANCEThe majority of pilot-caused airplane accidents occurduring the takeoff and landing phase of flight.Because of this fact, the pilot must be familiar with allthe variables that influence the takeoff and landingperformance of an airplane and must strive for exact-ing, professional procedures of operation during thesephases of flight.

Takeoff and landing performance is a condition ofaccelerated and decelerated motion. For instance,during takeoff, the airplane starts at zero speed andaccelerates to the takeoff speed to become airborne.During landing, the airplane touches down at thelanding speed and decelerates to zero speed.

The important factors of takeoff or landing performanceare as follows:

• The takeoff or landing speed which willgenerally be a function of the stall speed orminimum flying speed.

• The rate of acceleration and deceleration duringthe takeoff or landing roll. The acceleration anddeceleration experienced by any object variesdirectly with the imbalance of force and inverselywith the mass of the object.

• The takeoff or landing roll distance is a functionof both acceleration/deceleration and speed.

TAKEOFF PERFORMANCEThe minimum takeoff distance is of primary interest inthe operation of any airplane because it defines the run-way requirements. The minimum takeoff distance isobtained by taking off at some minimum safe speedthat allows sufficient margin above stall and providessatisfactory control and initial rate of climb. Generally,the lift-off speed is some fixed percentage of the stallspeed or minimum control speed for the airplane in thetakeoff configuration. As such, the lift-off will beaccomplished at some particular value of lift coeffi-

cient and angle of attack. Depending on the airplanecharacteristics, the lift-off speed will be anywhere from1.05 to 1.25 times the stall speed or minimum controlspeed.

To obtain minimum takeoff distance at the specificlift-off speed, the forces that act on the airplane mustprovide the maximum acceleration during the takeoffroll. The various forces acting on the airplane may ormay not be under the control of the pilot, and variousprocedures may be necessary in certain airplanes tomaintain takeoff acceleration at the highest value.

The powerplant thrust is the principal force to providethe acceleration and, for minimum takeoff distance, theoutput thrust should be at a maximum. Lift and dragare produced as soon as the airplane has speed, and thevalues of lift and drag depend on the angle of attackand dynamic pressure.

In addition to the important factors of proper pro-cedures, many other variables affect the takeoffperformance of an airplane. Any item that alters thetakeoff speed or acceleration rate during the takeoff rollwill affect the takeoff distance.

For example, the effect of gross weight on takeoff dis-tance is significant and proper consideration of thisitem must be made in predicting the airplane’s takeoffdistance. Increased gross weight can be considered toproduce a threefold effect on takeoff performance:

1. higher lift-off speed,

2. greater mass to accelerate, and

3. increased retarding force (drag and ground friction).If the gross weight increases, a greater speed is nec-essary to produce the greater lift necessary to get theairplane airborne at the takeoff lift coefficient. As anexample of the effect of a change in gross weight, a21 percent increase in takeoff weight will require a10 percent increase in lift-off speed to support thegreater weight.

A change in gross weight will change the net accelerat-ing force and change the mass that is being accelerated.If the airplane has a relatively high thrust-to-weightratio, the change in the net accelerating force is slightand the principal effect on acceleration is due to thechange in mass.

The takeoff distance will vary at least as the square ofthe gross weight. For example, a 10 percent increase intakeoff gross weight would cause:

• a 5 percent increase in takeoff velocity,

• at least a 9 percent decrease in rate of accelera-tion, and

• at least a 21 percent increase in takeoff distance.

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For the airplane with a high thrust-to-weight ratio, theincrease in takeoff distance might be approximately 21to 22 percent, but for the airplane with a relatively lowthrust-to-weight ratio, the increase in takeoff distancewould be approximately 25 to 30 percent. Such a pow-erful effect requires proper consideration of grossweight in predicting takeoff distance.

The effect of wind on takeoff distance is large, andproper consideration also must be provided when pre-dicting takeoff distance. The effect of a headwind is toallow the airplane to reach the lift-off speed at a lowergroundspeed while the effect of a tailwind is to requirethe airplane to achieve a greater groundspeed to attainthe lift-off speed.

A headwind that is 10 percent of the takeoff airspeed willreduce the takeoff distance approximately 19 percent.However, a tailwind that is 10 percent of the takeoff air-speed will increase the takeoff distance approximately21 percent. In the case where the headwind speed is 50percent of the takeoff speed, the takeoff distance wouldbe approximately 25 percent of the zero wind takeoffdistance (75 percent reduction).

The effect of wind on landing distance is identical tothe effect on takeoff distance. Figure 9-20 illustratesthe general effect of wind by the percent change intakeoff or landing distance as a function of the ratio ofwind velocity to takeoff or landing speed.

The effect of proper takeoff speed is especially important whenrunway lengths and takeoff distances are critical. The takeoffspeeds specified in the AFM/POH are generally the minimum

safe speeds at which the airplane can become airborne. Anyattempt to take off below the recommended speed could meanthat the airplane may stall, be difficult to control, or have a verylow initial rate of climb. In some cases, an excessive angle ofattack may not allow the airplane to climb out of ground effect.On the other hand, an excessive airspeed at takeoff mayimprove the initial rate of climb and “feel” of the airplane, butwill produce an undesirable increase in takeoff distance.Assuming that the acceleration is essentially unaffected, thetakeoff distance varies as the square of the takeoff velocity.

Thus, 10 percent excess airspeed would increase thetakeoff distance 21 percent. In most critical takeoffconditions, such an increase in takeoff distance wouldbe prohibitive, and the pilot must adhere to the recom-mended takeoff speeds.

The effect of pressure altitude and ambient temperatureis to define primarily the density altitude and its effecton takeoff performance. While subsequent correctionsare appropriate for the effect of temperature on certainitems of powerplant performance, density altitudedefines specific effects on takeoff performance. Anincrease in density altitude can produce a twofoldeffect on takeoff performance:

1. greater takeoff speed and

2. decreased thrust and reduced net acceleratingforce.

If an airplane of given weight and configuration isoperated at greater heights above standard sea level,the airplane will still require the same dynamic pres-sure to become airborne at the takeoff lift coefficient.Thus, the airplane at altitude will take off at the sameindicated airspeed as at sea level, but because of thereduced air density, the true airspeed will be greater.

The effect of density altitude on powerplant thrustdepends much on the type of powerplant. An increase inaltitude above standard sea level will bring an immedi-ate decrease in power output for the unsuperchargedreciprocating engine. However, an increase in altitudeabove standard sea level will not cause a decrease inpower output for the supercharged reciprocating engineuntil the altitude exceeds the critical operating altitude.For those powerplants that experience a decay in thrustwith an increase in altitude, the effect on the net acceler-ating force and acceleration rate can be approximated byassuming a direct variation with density. Actually, thisassumed variation would closely approximate the effecton airplanes with high thrust-to-weight ratios.

Proper accounting of pressure altitude (field elevationis a poor substitute) and temperature is mandatory foraccurate prediction of takeoff roll distance.

80

70

60

50

40

30

20

10

10

20

30

4040

50

60

0.3 0.2 0.1

0.1 0.2 0.3

Tailwind

Headwind

Percent Decreasein Takeoff or

Landing Distance

Ratio of Wind Velocityto Takeoff or Landing

Speed

Percent Increasein Takeoff or

Landing Distance

0

0

00

Figure 9-20. Effect of wind on takeoff and landing.

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The most critical conditions of takeoff performance arethe result of some combination of high gross weight,altitude, temperature, and unfavorable wind. In allcases, the pilot must make an accurate prediction oftakeoff distance from the performance data of theAFM/POH, regardless of the runway available, andstrive for a polished, professional takeoff procedure.

In the prediction of takeoff distance from theAFM/POH data, the following primary considerationsmust be given:

• Pressure altitude and temperature—to define theeffect of density altitude on distance.

• Gross weight—a large effect on distance.

• Wind—a large effect due to the wind or windcomponent along the runway.

• Runway slope and condition—the effect of anincline and the retarding effect of factors such assnow or ice.

LANDING PERFORMANCEIn many cases, the landing distance of an airplane willdefine the runway requirements for flying operations.The minimum landing distance is obtained by landingat some minimum safe speed, which allows sufficientmargin above stall and provides satisfactory controland capability for a go-around. Generally, the landingspeed is some fixed percentage of the stall speed orminimum control speed for the airplane in the landingconfiguration. As such, the landing will be accom-plished at some particular value of lift coefficient andangle of attack. The exact values will depend on theairplane characteristics but, once defined, the valuesare independent of weight, altitude, and wind.

To obtain minimum landing distance at the specifiedlanding speed, the forces that act on the airplane mustprovide maximum deceleration during the landing roll.The forces acting on the airplane during the landing rollmay require various procedures to maintain landingdeceleration at the peak value.

A distinction should be made between the proceduresfor minimum landing distance and an ordinary landingroll with considerable excess runway available.Minimum landing distance will be obtained by creatinga continuous peak deceleration of the airplane; that is,extensive use of the brakes for maximum deceleration.On the other hand, an ordinary landing roll with con-siderable excess runway may allow extensive use ofaerodynamic drag to minimize wear and tear on thetires and brakes. If aerodynamic drag is sufficient tocause deceleration of the airplane, it can be used in def-erence to the brakes in the early stages of the landing

roll; i.e., brakes and tires suffer from continuous harduse, but airplane aerodynamic drag is free and does notwear out with use. The use of aerodynamic drag isapplicable only for deceleration to 60 or 70 percent ofthe touchdown speed. At speeds less than 60 to 70 per-cent of the touchdown speed, aerodynamic drag is soslight as to be of little use, and braking must be utilizedto produce continued deceleration of the airplane.Since the objective during the landing roll is to deceler-ate, the powerplant thrust should be the smallestpossible positive value (or largest possible negativevalue in the case of thrust reversers).

In addition to the important factors of proper pro-cedures, many other variables affect the landingperformance. Any item that alters the landing speedor deceleration rate during the landing roll willaffect the landing distance.

The effect of gross weight on landing distance is one ofthe principal items determining the landing distance.One effect of an increased gross weight is that a greaterspeed will be required to support the airplane at thelanding angle of attack and lift coefficient.

For an example of the effect of a change in grossweight, a 21 percent increase in landing weight willrequire a 10 percent increase in landing speed to sup-port the greater weight.

When minimum landing distances are considered,braking friction forces predominate during the landingroll and, for the majority of airplane configurations,braking friction is the main source of deceleration.

The minimum landing distance will vary in direct pro-portion to the gross weight. For example, a 10 percentincrease in gross weight at landing would cause a:

• 5 percent increase in landing velocity and

• 10 percent increase in landing distance.

A contingency of this is the relationship betweenweight and braking friction force.

The effect of wind on landing distance is large anddeserves proper consideration when predicting landingdistance. Since the airplane will land at a particular air-speed independent of the wind, the principal effect ofwind on landing distance is due to the change in thegroundspeed at which the airplane touches down. Theeffect of wind on deceleration during the landing isidentical to the effect on acceleration during the take-off.

A headwind that is 10 percent of the landing airspeed willreduce the landing distance approximately 19 percent, but

Ch 09.qxd 10/24/03 7:23 AM Page 9-17

9-18

a tailwind that is 10 percent of the landing speed willincrease the landing distance approximately 21 percent.Figure 9-20 illustrates this general effect.

The effect of pressure altitude and ambient temperatureis to define density altitude and its effect on landingperformance. An increase in density altitude willincrease the landing speed but will not alter the netretarding force. Thus, the airplane at altitude will landat the same indicated airspeed as at sea level but,because of the reduced density, the true airspeed (TAS)will be greater. Since the airplane lands at altitude withthe same weight and dynamic pressure, the drag andbraking friction throughout the landing roll have thesame values as at sea level. As long as the condition iswithin the capability of the brakes, the net retardingforce is unchanged, and the deceleration is the same aswith the landing at sea level. Since an increase in alti-tude does not alter deceleration, the effect of densityaltitude on landing distance would actually be due tothe greater TAS.

The minimum landing distance at 5,000 feet would be16 percent greater than the minimum landing distanceat sea level. The approximate increase in landing dis-tance with altitude is approximately 3 1/2 percent foreach 1,000 feet of altitude. Proper accounting of den-sity altitude is necessary to accurately predict landingdistance.

The effect of proper landing speed is important whenrunway lengths and landing distances are critical. Thelanding speeds specified in the AFM/POH are gener-ally the minimum safe speeds at which the airplane canbe landed. Any attempt to land at below the specifiedspeed may mean that the airplane may stall, be difficultto control, or develop high rates of descent. On theother hand, an excessive speed at landing may improvethe controllability slightly (especially in crosswinds),but will cause an undesirable increase in landing dis-tance.

A 10 percent excess landing speed would cause at leasta 21 percent increase in landing distance. The excessspeed places a greater working load on the brakesbecause of the additional kinetic energy to be dissi-pated. Also, the additional speed causes increased dragand lift in the normal ground attitude, and the increasedlift will reduce the normal force on the braking sur-faces. The deceleration during this range of speedimmediately after touchdown may suffer, and it will bemore likely that a tire can be blown out from braking atthis point.

The most critical conditions of landing performanceare the result of some combination of high grossweight, high density altitude, and unfavorable wind.These conditions produce the greatest landing distance

and provide critical levels of energy dissipationrequired of the brakes. In all cases, it is necessary tomake an accurate prediction of minimum landingdistance to compare with the available runway. A pol-ished, professional landing procedure is necessarybecause the landing phase of flight accounts for morepilot-caused airplane accidents than any other singlephase of flight.

In the prediction of minimum landing distance fromthe AFM/POH data, the following considerations mustbe given:

• Pressure altitude and temperature—to define theeffect of density altitude.

• Gross weight—which defines the CAS forlanding.

• Wind—a large effect due to wind or windcomponent along the runway.

• Runway slope and condition—relatively smallcorrection for ordinary values of runway slope,but a significant effect of snow, ice, or softground.

PERFORMANCE SPEEDSTrue Airspeed (TAS) – the speed of the airplane in rela-tion to the air mass in which it is flying.

Indicated Airspeed (IAS) – the speed of the airplane asobserved on the airspeed indicator. It is the airspeedwithout correction for indicator, position (or installa-tion), or compressibility errors.

Calibrated Airspeed (CAS) – the airspeed indicatorreading corrected for position (or installation), andinstrument errors. (CAS is equal to TAS at sea level instandard atmosphere.) The color-coding for variousdesign speeds marked on airspeed indicators may beIAS or CAS.

Equivalent Airspeed (EAS) – the airspeed indicatorreading corrected for position (or installation), orinstrument error, and for adiabatic compressible flowfor the particular altitude. (EAS is equal to CAS at sealevel in standard atmosphere.)

VS0 – the calibrated power-off stalling speed or theminimum steady flight speed at which the airplane iscontrollable in the landing configuration.

VS1 – the calibrated power-off stalling speed or theminimum steady flight speed at which the airplane iscontrollable in a specified configuration.

VY – the calibrated airspeed at which the airplane willobtain the maximum increase in altitude per unit of

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time. This best rate-of-climb speed normally decreasesslightly with altitude.

VX – the calibrated airspeed at which the airplane willobtain the highest altitude in a given horizontal dis-tance. This best angle-of-climb speed normallyincreases slightly with altitude.

VLE – the maximum calibrated airspeed at which theairplane can be safely flown with the landing gearextended. This is a problem involving stability and con-trollability.

VLO – the maximum calibrated airspeed at which thelanding gear can be safely extended or retracted. Thisis a problem involving the air loads imposed on theoperating mechanism during extension or retraction ofthe gear.

VFE – the highest calibrated airspeed permissible withthe wing flaps in a prescribed extended position. Thisis because of the air loads imposed on the structure ofthe flaps.

VA – the calibrated design maneuvering airspeed. Thisis the maximum speed at which the limit load can beimposed (either by gusts or full deflection of the con-trol surfaces) without causing structural damage.

VNO – the maximum calibrated airspeed for normaloperation or the maximum structural cruising speed.This is the speed at which exceeding the limit load fac-tor may cause permanent deformation of the airplanestructure.

VNE – the calibrated airspeed which should NEVER beexceeded. If flight is attempted above this speed, struc-tural damage or structural failure may result.

PERFORMANCE CHARTSPerformance charts allow a pilot to predict thetakeoff, climb, cruise, and landing performanceof the airplane. These charts, provided by themanufacturer, are included in the AFM/POH. Theinformation the manufacturer provides on thesecharts has been gathered from test flights con-ducted in a new airplane, under normal operatingconditions while using average piloting skills,and with the airplane and engine in good workingorder. Engineers record the flight data and createperformance charts based on the behavior of theairplane during the test flights. By using theseperformance charts, a pilot can determine therunway length needed to take off and land, theamount of fuel that will be used during flight,and the length of time it will take to arrive at thedestination. It is important to remember that thedata from the charts will not be accurate if theairplane is not in good working order or whenoperating under adverse conditions. So take intoconsideration that it is necessary to compensatethe performance numbers if the airplane is not ingood working order or piloting skills are belowaverage. Each airplane performs differently andtherefore, has different performance numbers.Compute the performance of the airplane prior toevery flight, as every flight is different.

Every chart is based on certain conditions and containsnotes on how to adapt the information for flight condi-tions. It is important to read every chart and understandhow to use it. Read the accompanying instructions providedby the manufacturer. For an explanation on how to use thecharts, refer to the example provided by the manufacturerfor that specific chart. [Figure 9-21]

Figure 9-21. Carefully read all conditions and notes for every chart.

Ch 09.qxd 10/24/03 7:23 AM Page 9-19

9-20

The information manufacturers furnish is not stan-dardized. Information may be contained in a table for-mat, and other information may be contained in agraph format. Sometimes combined graphs incorpo-rate two or more graphs into one chart to compensatefor multiple conditions of flight. Combined graphsallow the pilot to predict airplane performance forvariations in density altitude, weight, and winds all onone chart. Because of the vast amount of informationthat can be extracted from this type of chart, it isimportant to be very accurate in reading the chart. Asmall error in the beginning can lead to a large error atthe end.

The remainder of this section covers performanceinformation for airplanes in general and discusseswhat information the charts contain and how toextract information from the charts by direct readingand interpolation methods. Every chart contains awealth of information that should be used when flightplanning. Examples of the table, graph, and combinedgraph formats for all aspects of flight will be dis-cussed.

INTERPOLATIONNot all of the information on the charts is easilyextracted. Some charts require interpolation to findthe information for specific flight conditions.Interpolating information means that by taking theknown information, a pilot can compute intermediateinformation. However, pilots sometimes round offvalues from charts to a more conservative figure.

Using values that reflect slightly more adverse condi-tions provides a reasonable estimate of performanceinformation and gives a slight margin of safety. Thefollowing illustration is an example of interpolatinginformation from a takeoff distance chart. [Figure9-22]

DENSITY ALTITUDE CHARTSUse a density altitude chart to figure the densityaltitude at the departing airport. Using figure 9-23,determine the density altitude based on the giveninformation.

Sample Problem 1Airport Elevation...........................................5,883 feetOAT........................................................................70°FAltimeter....................................................30.10 in. Hg

First, compute the pressure altitude conversion. Find30.10 under the altimeter heading. Read across to thesecond column. It reads “-165.” Therefore, it is neces-sary to subtract 165 from the airport elevation givinga pressure altitude of 5,718 feet. Next, locate the out-side air temperature on the scale along the bottom ofthe graph. From 70°, draw a line up to the 5,718 feetpressure altitude line, which is about two-thirds of theway up between the 5,000 and 6,000-foot lines. Drawa line straight across to the far left side of the graphand read the approximate density altitude. Theapproximate density altitude in thousands of feet is7,700 feet.

To find the takeoff distance for a pressure altitude of 2,500 feetat 20°C, average the ground roll for 2,000 feet and 3,000 feet.

1,115 + 1,2302

= 1,173 feet

Figure 9-22. Interpolating charts.

Ch 09.qxd 10/24/03 7:23 AM Page 9-20

9-21

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Ch 09.qxd 10/24/03 7:23 AM Page 9-21

9-22

TAKEOFF CHARTSTakeoff charts are typically provided in several forms.They allow a pilot to compute the takeoff distance ofthe airplane with no flaps or with a specific flap config-uration. A pilot can also compute distances for a no flaptakeoff over a 50-foot obstacle scenario as well as withflaps over a 50-foot obstacle. The takeoff distance chartprovides for various airplane weights, altitudes,temperatures, winds, and obstacle heights.

Sample Problem 2Pressure Altitude............................................2,000 feetOAT.......................................................................22°CTakeoff Weight.........................................2,600 poundsHeadwind...........................................................6 knotsObstacle Height....................................50-foot obstacle

Refer to figure 9-24. This chart is an example of a com-bined takeoff distance graph. It takes into considerationpressure altitude, temperature, weight, wind, and obsta-cles all on one chart. First, find the correct temperatureon the bottom left-hand side of the graph. Follow theline from 22°C straight up until it intersects the 2,000-foot altitude line. From that point, draw a line straightacross to the first dark reference line. Continue to drawthe line from the reference point in a diagonal directionfollowing the surrounding lines until it intersects thecorresponding weight line. From the intersection of

2,600 pounds, draw a line straight across until itreaches the second reference line. Once again,follow the lines in a diagonal manner until it reachesthe 6-knot headwind mark. Follow straight across tothe third reference line and from here, draw a line intwo directions. First, draw a line straight across tofigure the ground roll distance. Next, follow thediagonal lines again until it reaches the correspon-ding obstacle height. In this case, it is a 50-footobstacle. Therefore, draw the diagonal line to the faredge of the chart. This results in a 600-foot groundroll distance and a total distance of 1,200 feet over a50-foot obstacle. To find the corresponding takeoffspeeds at lift-off and over the 50-foot obstacle, referto the table on the top of the chart. In this case, thelift-off speed at 2,600 pounds would be 63 knots andover the 50-foot obstacle would be 68 knots.

Sample Problem 3Pressure Altitude............................................3,000 feetOAT........................................................................30°CTakeoff Weight.........................................2,400 poundsHeadwind.........................................................18 knots

Refer to figure 9-25. This chart is an example of atakeoff distance table for short-field takeoffs. For thistable, first find the takeoff weight. Once at 2,400pounds, begin reading from left to right across the

ASSOCIATED CONDITIONS

POWER

MIXTURE

FLAPSLANDING GEAR

COWL FLAPS

FULL THROTTLE2600 RPMLEAN TO APPROPRIATEFUEL PRESSUREUPRETRACT AFTER POSITIVECLIMB ESTABLISHEDOPEN

WEIGHT

POUNDS KNOTS MPH

TAKEOFF SPEEDLIFT–OFF 50 FT

KNOTS MPH29502800260024002200

6664636158

7674727067

7270686663

8381787673

~

TAKEOFF DISTANCE

–40 –30 –20 –10 0 10 20 30 40 50

OUTSIDE AIR TEMPERATURE ~ °C

OUTSIDE AIR TEMPERATURE ~ °F

–40 –20 0 20 40 60 80 100 120

WEIGHT~POUNDS

2800 2600 2400 2200

WIND COMPONENT ~KNOTS

OBSTACLE HEIGHT ~FEET

0 10 20 30 0 50

6000

5000

4000

3000

2000

1000

0

10000

8000

6000

4000

2000S.L.

PRESSURE ALTITUDE~FEET

ISA

RE

FE

RE

NC

E L

INE

RE

FE

RE

NC

E L

INE

RE

FE

RE

NC

E L

INE

TAIL

WIN

D

HEADWIND

GUID

E LI

NES N

OT

APPLI

CABLE F

OR

INTE

RMED

IATE

OBST

ACLE H

EIG

HTS

Figure 9-24. Combined takeoff distance graph.

Ch 09.qxd 10/24/03 7:23 AM Page 9-22

9-23

table. The takeoff speed is in the second column and, inthe third column under pressure altitude, find the pres-sure altitude of 3,000 feet. Carefully follow that line tothe right until it is under the correct temperature columnof 30°C. The ground roll total reads 1,325 feet and thetotal required to clear a 50-foot obstacle is 2,480 feet. Atthis point, there are 18 knots of headwind. Reading inthe notes section under point number two, it says todecrease the distances by 10 percent for each 9 knots ofheadwind. With 18 knots of headwind, it is necessary todecrease the distance by 20 percent. Multiply 1,325 feetby 20 percent or by .20 (1325 x .20 = 265), then subtractthat amount from the total distance (1325 – 265 = 1060).Repeat this process for the total distance over a 50-footobstacle. The ground roll distance is 1,060 feet and thetotal distance over a 50-foot obstacle is 1,984 feet.

CLIMB AND CRUISE CHARTSClimb and cruise chart information is based on actualflight tests conducted in an airplane of the same type.This information is extremely useful when planning across-country to predict the performance and fuelconsumption of the airplane. Manufacturers produce

several different charts for climb and cruise perform-ance. These charts will include everything from fuel,time, and distance to climb, to best power settingduring cruise, to cruise range performance.

The first chart to check for climb performance is a fuel,time, and distance-to-climb chart. This chart will givethe fuel amount used during the climb, the time it willtake to accomplish the climb, and the ground distancethat will be covered during the climb. To use this chart,obtain the information for the departing airport and forthe cruise altitude. Using figure 9-26, calculate the fuel,time, and distance to climb based on the informationprovided.

Sample Problem 4Departing Airport Pressure Altitude..............6,000 feetDeparting Airport OAT..........................................25°CCruise Pressure Altitude..............................10,000 feetCruise OAT............................................................10°C

First, find the information for the departing airport.Find the OAT for the departing airport along the bot-tom, left-hand side of the graph. Follow the line from

WEIGHT

2200

2000

PRESSALTFT

S.L.10002000

40005000600070008000

S.L.10002000300040005000600070008000

S.L.10002000300040005000600070008000

GRNDROLL

FT

795875960

105511651285142515801755

650710780855945

1040115012701410

525570625690755830920

10151125

TOTAL FTTO CLEAR50 FT OBS

146016051770196021852445275531403615

119513101440158517501945217024402760

97010601160127014001545171019002125

GRNDROLL

FT

860940

1035114012601390154017101905

700765840925

10201125124013751525

565615675740815900990

10951215

TOTAL FTTO CLEAR50 FT OBS

157017251910212023652660301534504015

128014051545170518902105235526553015

103511351240136515001660184520552305

GRNDROLL

FT

99510901200

1465162018002000- - -

805885975

107011801305144516051785

650710780860945

2145240527151410

TOTAL FTTO CLEAR50 FT OBS

181020002220

2790316036204220- - -

147016151785197522002465277531553630

118512951425157017351925214524052715

GRNDROLL

FT

1065117012901425157517451940- - - - - -

865 950

1045115012701405155517301925

695765840920

10151120123513701520

TOTAL FTTO CLEAR50 FT OBS

1945215523952685303034553990- - - - - -

157517351915213023752665302034504005

126513851525168518652070231526052950

LIFTOFF

51

49

46

AT 50 FT

56

54

51

TAKEOFFSPEED KIAS 0 °C 10 °C 20 °C 30 °C

GRNDROLL

FT

92510151115123013551500166518502060

750825905995

11001210134014851650

605665725800880970

107011801310

TOTAL FTTO CLEAR50 FT OBS

168518602060229525702895330038054480

137515101660183520402275255528903305

111012151330146516151790199022252500

40 °C

TAKEOFF DISTANCEMAXIMUM WEIGHT 2400 LB

SHORT FIELD

CONDITIONS:Flaps 10°Full Throttle Prior to Brake ReleasePaved Level RunwayZero Wind

NOTES:1. Prior to takeoff from fields above 3000 feet elevation, the mixture should be leaned to give maximum RPM in a full throttle, static runup.2. Decrease distances 10% for each 9 knots headwind. For operation with tailwind up to 10 knots, increase distances by 10% for each 2 knots.3. For operation on a dry, grass runway, increase distances by 15% of the "ground roll" figure.

LB

2400

3000 1325 2480

Figure 9-25.Takeoff distance table, short-field.

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9-24

25°C straight up until it intersects the line correspon-ding to the pressure altitude of 6,000 feet. Continue thisline straight across until it intersects all three lines forfuel, time, and distance. Draw a line straight down fromthe intersection of altitude and fuel, altitude and time,and a third line at altitude and distance. It should read3.5 gallons of fuel, 6.5 minutes of time, and 9 nauticalmiles. Next, repeat the steps to find the information forthe cruise altitude. It should read 6.5 gallons of fuel,11.5 minutes of time, and 15 nautical miles. Take eachset of numbers for fuel, time, and distance and subtractthem from one another (6.5 - 3.5 = 3 gallons of fuel). Itwill take 3 gallons of fuel and 5 minutes of time toclimb to 10,000 feet. During that climb, the distancecovered is 6 nautical miles. Remember, according tothe notes at the top of the chart, these numbers do nottake into account wind, and it is assumed maximumcontinuous power is being used.

The next example is a fuel, time, and distance-to-climbtable. For this table, use the same basic criteria as forthe previous chart. However, it is necessary to figure

the information in a different manner. Refer to figure9-27 to work the following sample problem.

Sample Problem 5Departing Airport Pressure Altitude..............Sea LevelDeparting Airport OAT..........................................22°CCruise Pressure Altitude................................8,000 feetTakeoff Weight.........................................3,400 pounds

To begin, find the given weight of 3,400 in thefirst column of the chart. Move across to the pres-sure altitude column to find the sea level altitudenumbers. At sea level, the numbers read zero.Next, read the line that corresponds with thecruising altitude of 8,000 feet. Normally, a pilotwould subtract these two sets of number from oneanother, but given the fact that the numbers readzero at sea level, it is known that the time to climbfrom sea level to 8,000 feet is 10 minutes. It isalso known that 21 pounds of fuel will be used and20 nautical miles will be covered during theclimb. However, the temperature is 22°C, which is7º above the standard temperature of 15°C. Thenotes section of this chart indicate that our findings must

Figure 9-26. Fuel, time, and distance-to-climb chart.

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9-25

be increased by 10 percent for each 7º abovestandard. Multiply the findings by 10 percent or.10 (10 x .10 = 1, 1 + 10 = 11 minutes). Afteraccounting for the additional 10 percent, the find-ings should read 11 minutes, 23.1 pounds of fuel,and 22 nautical miles. Notice that the fuel isreported in pounds of fuel, not gallons. Aviationfuel weighs 6 pounds per gallon, so 23.1 poundsof fuel is equal to 3.85 gallons of fuel (23.1 / 6 =3.85).

The next example is a cruise and range performancechart. This type of table is designed to give true air-speed, fuel consumption, endurance in hours, and rangein miles at specific cruise configurations. Use figure 9-28 to determine the cruise and range performanceunder the given conditions.

Sample Problem 6Pressure Altitude............................................5,000 feetRPM............................................................2,400 r.p.m.Fuel Carrying Capacity...............38 gallons, no reserve

Find 5,000 feet pressure altitude in the first column onthe left-hand side of the table. Next, find the correctr.p.m. of 2,400 in the second column. Follow that linestraight across and read the TAS of 116 m.p.h., and afuel burn rate of 6.9 gallons per hour. As per theexample, the airplane is equipped with a fuel carryingcapacity of 38 gallons. Under this column, read thatthe endurance in hours is 5.5 hours and the range inmiles is 635 miles.

Figure 9-27. Fuel, time, and distance-to-climb table.

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9-26

Cruise power setting tables are useful when planningcross-country flights. The table gives the correct cruisepower settings as well as the fuel flow and airspeed per-formance numbers at that altitude and airspeed.

Sample Problem 7Pressure Altitude @ Cruise............................6,000 feetOAT...............................................36°F above standard

Refer to figure 9-29 for this sample problem. First,locate the pressure altitude of 6,000 feet on the far leftside of the table. Follow that line across to the far rightside of the table under the 20°C (or 36°F) column. At6,000 feet, the r.p.m. setting of 2,450 will maintain 65

percent continuous power at 21.0 inches of manifoldpressure with a fuel flow rate of 11.5 gallons per hourand airspeed of 161 knots.

Another type of cruise chart is a best power mixturerange graph. This graph gives the best range based onpower setting and altitude. Using figure 9-30, find therange at 65 percent power with and without a reservebased on the provided conditions.

Sample Problem 8OAT..................................................................StandardPressure Altitude............................................5,000 feet

Figure 9-28. Cruise and range performance.

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9-27

First, move up the left side of the graph to 5,000 feetand standard temperature. Follow the line straightacross the graph until it intersects the 65 percent lineunder both the reserve and no reserve categories. Draw

a line straight down from both intersections to the bot-tom of the graph. At 65 percent power with a reserve,the range is approximately 522 miles. At 65 percentpower with no reserve, the range should be 581 miles.

CRUISE POWER SETTINGS65% MAXIMUM CONTINUOUS POWER (OR FULL THROTTLE)

2800 POUNDS

STANDARD DAY (ISA)ISA –20 °C (–36 °F)

PRESSALT. IOAT

ENGINESPEED

MAN.PRESS

FUELFLOWPER

ENGINE TAS IOATENGINESPEED

MAN.PRESS

FUELFLOWPER

ENGINE TAS IOATENGINESPEED

MAN.PRESS

FUELFLOWPER

ENGINE TAS

°F °CFEET RPM IN HG PSI GPH KTS MPH °F °C RPM IN HG PSI GPH KTS MPH °F °C RPM IN HG PSI GPH KTS MPH

SL20004000

800010000120001400016000

2719125

-2-8

-15-22-29

-3-7

-11-15-19-22-26-30-34

245024502450245024502450245024502450

245024502450245024502450245024502450

245024502450

24502450245024502450

20.720.420.119.819.519.218.817.416.1

6.66.66.66.66.66.66.45.85.3

6.66.66.66.66.66.66.15.65.1

6.66.66.6

6.66.55.95.44.9

11.511.511.511.511.511.511.310.59.7

11.511.511.511.511.511.510.910.19.4

11.511.511.5

11.511.410.69.89.1

147149152155157160162159156

169171175178181184186183180

63554841362821147

1713952

-2-6

-10-14

21.221.020.720.420.219.918.817.416.1

150153156158161163163160156

173176180182185188188184180

999184

7264575043

373329

221814106

21.821.521.3

20.820.318.817.416.1

153156159

164166163160155

176180183

189191188184178

NOTES: 1. Full throttle manifold pressure settings are approximate. 2. Shaded area represents operation with full throttle.

ISA +20 °C (+36 °F)

2450 6.6 11.579 26 21.0 161 1856000

Figure 9-29. Cruise power setting table.

Figure 9-30. Best power mixture range graph.

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9-28

The last cruise chart referenced is a cruise performancegraph. This graph is designed to tell the true airspeed(TAS) performance of the airplane depending on thealtitude, temperature, and power setting. Using figure9-31, find the TAS performance based on the giveninformation.

Sample Problem 9OAT........................................................................16°CPressure Altitude............................................6,000 feetPower Setting.............................65 percent, best powerWheel Fairings..........................................Not installed

Begin by finding the correct OAT on the bottom,left-hand side of the graph. Move up that line untilit intersects the pressure altitude of 6,000 feet.Draw a line straight across to the 65 percent, bestpower line. This is the solid line, not the dashedline, which represents best economy. Draw a linestraight down from this intersection to the bottomof the graph. The true airspeed at 65 percent bestpower is 140 knots. However, it is necessary to sub-tract 8 knots from the speed since there are nowheel fairings. This note is listed under the title andconditions. The true airspeed will be 132 knots.

CROSSWIND AND HEADWINDCOMPONENT CHARTEvery airplane is tested according to FAA regulationsprior to certification. The airplane is tested by a pilotwith average piloting skills in 90° crosswinds with avelocity up to 0.2 VSO or two-tenths of the airplane’sstalling speed with power off, gear down, and flapsdown. This means that if the stalling speed of the air-plane is 45 knots, it must be capable of being landed ina 9 knot, 90° crosswind. The maximum demonstratedcrosswind component is published in the AFM/POH.The crosswind and headwind component chart allowsfor figuring the headwind and crosswind componentfor any given wind direction and velocity.

Sample Problem 10Runway......................................................................17Wind....................................................140° @ 25 knots

Refer to figure 9-32 to solve this problem. First,determine how many degrees difference there isbetween the runway and the wind direction. It isknown that runway 17 means a direction of 170° andfrom that, subtract the wind direction of 140°. Thisgives a 30° angular difference. This is the wind angle.Next, locate the 30° mark and draw a line from thereuntil it intersects the correct wind velocity of 25

Figure 9-31. Cruise performance graph.

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knots. From there, draw a line straight down and a linestraight across. The headwind component is 22 knotsand the crosswind component is 13 knots. This infor-mation is important when taking off and landing sothat, first of all, the appropriate runway can be pickedif more than one exists at a particular airport, but alsoso that the airplane is not pushed beyond its testedlimits.

LANDING CHARTSLanding performance is affected by variables similarto those affecting takeoff performance. It is necessaryto compensate for differences in density altitude,weight of the airplane, and headwinds. Like takeoffperformance charts, landing distance information isavailable as normal landing information as well aslanding distance over a 50-foot obstacle. As usual,read the associated conditions and notes in order to

ascertain the basis of the chart information.Remember, when calculating landing distance that thelanding weight will not be the same as the takeoffweight. The weight must be recalculated to compen-sate for the fuel that was used during the flight.

Sample Problem 11Pressure Altitude............................................1,250 feetTemperature.....................................................Standard

Refer to figure 9-33. This example makes use of alanding distance table. Notice that the altitude of1,250 feet is not on this table. It is therefore necessaryto use interpolation skills to find the correct landingdistance. The pressure altitude of 1,250 is halfwaybetween sea level and 2,500 feet. First, find the columnfor sea level and the column for 2,500 feet. Take thetotal distance of 1,075 for sea level and the total

CROSSWIND COMPONENT

HE

AD

WIN

D C

OM

PO

NE

NT

WIND VELOCITY

0° 10°20°

30°

40°

50°

60°

70°

80°

90°605040302010

60

50

40

30

20

10

Figure 9-32. Crosswind component chart.

LANDING DISTANCE FLAPS LOWERED TO 40 ° - POWER OFFHARD SURFACE RUNWAY - ZERO WIND

GROSSWEIGHT

LB

APPROACHSPEED

IAS, MPHGROUND

ROLLGROUND

ROLLGROUND

ROLLGROUND

ROLL

TOTALTO CLEAR50 FT OBS

TOTALTO CLEAR50 FT OBS

TOTALTO CLEAR50 FT OBS

TOTALTO CLEAR50 FT OBS

AT SEA LEVEL & 59 °F AT 2500 FT & 50 °F AT 5000 FT & 41 °F AT 7500 FT & 32 °F

1600 60 445 1075 470 1135 495 1195 520 1255

NOTES: 1. Decrease the distances shown by 10% for each 4 knots of headwind.2. Increase the distance by 10% for each 60 °F temperature increase above standard.3. For operation on a dry, grass runway, increase distances (both "ground roll" and "total to clear 50 ft obstacle") by 20% of the "total to clear 50 ft obstacle" figure.

Figure 9-33. Landing distance table.

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distance of 1,135 for 2,500 and add them together.Divide the total by two to obtain the distance for 1,250feet. The distance is 1,105 feet total landing distance toclear a 50-foot obstacle. Repeat this process to obtainthe ground roll distance for the pressure altitude. Theground roll should be 457.5 feet.

Sample Problem 12OAT........................................................................57°FPressure Altitude............................................4,000 feetLanding Weight........................................2,400 poundsHeadwind...........................................................6 knotsObstacle Height..................................................50 foot

Using the given conditions and figure 9-34, determinethe landing distance for the airplane. This graph is anexample of a combined landing distance graph andallows compensation for temperature, weight, head-winds, tailwinds, and varying obstacle height. Beginby finding the correct OAT on the Fahrenheit scale onthe left-hand side of the chart. Move up in a straightline to the correct pressure altitude of 4,000 feet. Fromthis intersection, move straight across to the first darkreference line. Follow the lines in the same diagonalfashion until the correct landing weight is reached. At2,400 pounds, continue in a straight line across to thesecond dark reference line. Once again, draw a line in a

diagonal manner to the correct wind component andthen straight across to the third dark reference line.From this point, draw a line in two separate directions:one straight across to figure the ground roll and one ina diagonal manner to the correct obstacle height. Thisshould be 900 feet for the total ground roll and 1,300feet for the total distance over a 50-foot obstacle.

STALL SPEED PERFORMANCE CHARTSStall speed performance charts are designed to give anunderstanding of the speed at which the airplane willstall in a given configuration. This type of chart willtypically take into account the angle of bank, the posi-tion of the gear and flaps, and the throttle position. Usefigure 9-35 and the accompanying conditions to findthe speed at which the airplane will stall.

Sample Problem 13Power......................................................................OFFFlaps.....................................................................DownGear......................................................................DownAngle of Bank..........................................................45°

First, locate the correct flap and gear configuration.The bottom half of the chart should be used since thegear and flaps are down. Next, choose the row corre-sponding to a power-off situation. Now find the correct

PRESSURE ALTITUDE~FEET

100008000

6000

20004000

SLISA

–40 –30 –20 –10 0 10 20 30 40 50

OUTSIDE AIR TEMPERATURE ~ °C

OUTSIDE AIR TEMPERATURE ~ °F

–40 –20 0 20 40 60 80 100 120

WEIGHT~POUNDS

2800 2600 2400 2200

WIND COMPONENT ~KNOTS

OBSTACLE HEIGHT ~FEET

0 10 20 30 0 50

3500

3000

2500

2000

1500

1000

500

DIS

TAN

CE

~ F

EE

T

RE

FE

RE

NC

E L

INE

RE

FE

RE

NC

E L

INE

RE

FE

RE

NC

E L

INE

HEADWIND

TAIL

WIN

D

GUIDELI

NES NOT

APPLICABLE

FOR

INTE

RMEDIA

TE

OBST

ACLE H

EIG

HTS

POWER

FLAPSLANDING GEARRUNWAYAPPROACH SPEEDBRAKING

RETARDED TO MAINTAIN900 FT/on FINAL APPROACHDOWNDOWNPAVED, LEVEL, DRY SURFACEIAS AS TABULATEDMAXIMUM

ASSOCIATED CONDITIONS: WEIGHT~

POUNDS

SPEEDAT 50 FT

KNOTS MPH

29502800260024002200

7068656360

8078757269

LANDING DISTANCE

Figure 9-34. Landing distance graph.

Ch 09.qxd 10/24/03 7:23 AM Page 9-30

9-31

angle of bank column, which is 45°. The stall speed inmiles per hour (m.p.h.) is 78 m.p.h., and the stall speedin knots would be 68 knots.

Performance charts provide valuable information to thepilot. Take advantage of these charts. A pilot can pre-dict the performance of the airplane under most flyingconditions, and this enables a better plan for everyflight. The Code of Federal Regulations (CFR) requiresthat a pilot be familiar with all information availableprior to any flight. Pilots should use the information totheir advantage as it can only contribute to safety inflight.

TRANSPORT CATEGORYAIRPLANE PERFORMANCETransport category airplanes are certificated under Title14 of the Code of Federal Regulations (14 CFR) part25. The airworthiness certification standards of part 25require proven levels of performance and guaranteedsafety margins for these airplanes, regardless of thespecific operating regulations under which they areemployed.

MAJOR DIFFERENCES IN TRANSPORTCATEGORY VERSUS NON-TRANSPORTCATEGORY PERFORMANCEREQUIREMENTS

• Full Temperature AccountabilityAll of the performance charts for the transportcategory airplanes require that takeoff and climb

performance be computed with the full effects oftemperature considered.

• Climb Performance Expressed as PercentGradient of ClimbThe transport category airplane’s climb perform-ance is expressed as a percent gradient of climbrather than a figure calculated in feet per minuteof climb. This percent gradient of climb is a muchmore practical expression of performance since itis the airplane’s angle of climb that is critical inan obstacle clearance situation.

• Change in Lift-off TechniqueLift-off technique in transport category air-planes allows the reaching of V2 (takeoff safetyspeed) after the airplane is airborne. This ispossible because of the excellent accelerationand reliability characteristics of the engines onthese airplanes and also because of the largersurplus of power.

• Performance Requirements Applicable to allSegments of AviationAll airplanes certificated by the FAA in thetransport category, whatever the size, must beoperated in accordance with the same perform-ance criteria. This applies to both commercialand non-commercial operations.

PERFORMANCE REQUIREMENTSThe performance requirements that the transport cate-gory airplane must meet are as follows:

TAKEOFF

• Takeoff speeds

• Takeoff runway required

• Takeoff climb required

• Obstacle clearance requirements

LANDING

• Landing speeds

• Landing runway required

• Landing climb required

TAKEOFF PLANNINGThe following are the speeds that affect the transportcategory airplane’s takeoff performance. The flightcrew must be thoroughly familiar with each of thesespeeds and how they are used in takeoff planning.

Figure 9-35. Stall speed table.

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9-32

All of the above V speeds should be considered duringevery takeoff. The V1, VR, V2 and VFS speeds should bevisibly posted in the cockpit for reference duringthe takeoff.

Takeoff speeds vary with airplane weight. Before take-off speeds can be computed, the pilot must first deter-mine the maximum allowable takeoff weight. The threeitems that can limit takeoff weight are runway require-

ments, takeoff climb requirements, and obstacle clear-ance requirements.

RUNWAY REQUIREMENTSThe runway requirements for takeoff will be affectedby the following:

• Pressure altitude

• Temperature

• Headwind component

• Runway gradient or slope

• Airplane weight

The runway required for takeoff must be based uponthe possible loss of an engine at the most critical point,which is at V1 (decision speed). By regulation, the air-plane’s takeoff weight has to accommodate the longestof three distances:

1. Accelerate-Go DistanceThe distance required to accelerate to V1 with allengines at takeoff power, experience an enginefailure at V1 and continue the takeoff on theremaining engine(s). The runway requiredincludes the distance required to climb to 35 feetby which time V2 speed must be attained.

2. Accelerate-Stop DistanceThe distance required to accelerate to V1 with allengines at takeoff power, experience an enginefailure at V1, and abort the takeoff and bring theairplane to a stop using braking action only (useof thrust reversing is not considered).

3. Takeoff DistanceThe distance required to complete an all-enginesoperative takeoff to the 35-foot height. It must beat least 15 percent less than the distance requiredfor a one-engine inoperative engine takeoff. Thisdistance is not normally a limiting factor as it isusually less than the one-engine inoperative take-off distance.

These three required takeoff runway considerations areshown in figure 9-36.

BALANCED FIELD LENGTHIn most cases, the pilot will be working with a per-formance chart for takeoff runway required, which willgive “balanced field length” information. This meansthat the distance shown for the takeoff will include boththe accelerate-go and accelerate-stop distances. One

Speed Definition

VS Stalling speed or the minimum steady flight speed at which the airplane is controllable.

VMCG Minimum control speed on the ground, with one engine inoperative, (critical engine on two-engine airplanes) takeoff power on other engine(s), using aerodynamic controls only for directional control. (Must be less than V1).

VMCA Minimum control speed in the air, with one engine inoperative, (critical engine on two-engine airplanes) operating engine(s) at takeoff power, maximum of 5˚ bank into the good engine(s).

V1 Critical engine failure speed or decision speed.Engine failure below this speed shall result in an aborted takeoff; above this speed the takeoff run should be continued.

VR Speed at which the rotation of the airplane is initiated to takeoff attitude. This speed cannot be less than V1 or less than 1.05 times VMC. With an engine failure, it must also allow for the acceleration to V2 at the 35-foot height at the end of the runway.

VLO Lift-off speed. The speed at which the airplanefirst becomes airborne.

V2 The takeoff safety speed which must be attained at the 35-foot height at the end of the required runway distance. This is essentially the best one-engine inoperative angle of climb speed for the airplane and should be held until clearing obstacles after takeoff, or until at least400 feet above the ground.

VFS Final segment climb speed, which is based upon one-engine inoperative climb, clean configuration, and maximum continuous power setting.

Ch 09.qxd 10/24/03 7:23 AM Page 9-32

9-33

effective means of presenting the normal takeoff data isshown in the tabulated chart in figure 9-37.

The chart in figure 9-37 shows the runway distancerequired under normal conditions and is useful as aquick reference chart for the standard takeoff. The Vspeeds for the various weights and conditions are alsoshown.

For other than normal takeoff conditions, such as withengine anti-ice, anti-skid brakes inoperative, orextremes in temperature or runway slope, the pilotshould consult the appropriate takeoff performance

charts in the performance section of the Airplane FlightManual.

There are other occasions of very high weight andtemperature where the runway requirement may bedictated by the maximum brake kinetic energy limitsthat affect the airplane’s ability to stop. Under theseconditions, the accelerate-stop distance may begreater than the accelerate-go. The procedure to bringperformance back to a balanced field takeoff condi-tion is to limit the V1 speed so that it does not exceedthe maximum brake kinetic energy speed (sometimescalled VBE). This procedure also results in areduction in allowable takeoff weight.

TAKEOFF DISTANCE WITHAN ENGINE FAILURE

V1 VR VLO V2

35'

1– ENGINEACCELERATION

ALL – ENGINEACCELERATION

V1

ALL – ENGINEACCELERATION

ACCELERATE/STOPDISTANCE

STOP DISTANCE

V1 VR VLO

35'

ALL – ENGINE TAKEOFF DISTANCE TO 35' 15%MARGIN

ALL – ENGINE TAKEOFF FIELD LENGTH

115% ALL – ENGINE TAKEOFF DISTANCE

Figure 9-36. Minimum required takeoff runway lengths.

Ch 09.qxd 10/24/03 7:23 AM Page 9-33

9-34

CLIMB REQUIREMENTSAfter the airplane has reached the 35-foot height withone engine inoperative, there is a requirement that it beable to climb at a specified climb gradient. This isknown as the takeoff flightpath requirement. The air-plane’s performance must be considered based upon aone-engine inoperative climb up to 1,500 feet abovethe ground.

The takeoff flightpath profile with required gradientsof climb for the various segments and configurationsis shown in figure 9-38.

Note: Climb gradient can best be described as being acertain gain of vertical height for a given distance cov-ered horizontally. For instance, a 2.4 percent gradientmeans that 24 feet of altitude would be gained for each

Figure 9-37. Normal takeoff runway required.

Ch 09.qxd 10/24/03 7:24 AM Page 9-34

9-35

1,000 feet of distance covered horizontally across theground.

The following brief explanation of the one-engineinoperative climb profile may be helpful in understand-ing the chart in figure 9-38.

FIRST SEGMENTThis segment is included in the takeoff runwayrequired charts and is measured from the point at whichthe airplane becomes airborne until it reaches the 35-foot height at the end of the runway distance required.Speed initially is VLO and must be V2 at the 35-footheight.

SECOND SEGMENTThis is the most critical segment of the profile. The sec-ond segment is the climb from the 35-foot height to 400feet above the ground. The climb is done at full takeoffpower on the operating engine(s), at V2 speed, and withthe flaps in the takeoff configuration. The requiredclimb gradient in this segment is 2.4 percent for two-engine airplanes, 2.7 percent for three-engine airplanes,and 3.0 percent for four-engine airplanes.

THIRD OR ACCELERATION SEGMENTDuring this segment, the airplane is considered to bemaintaining the 400 feet above the ground and acceler-ating from the V2 speed to the VFS speed before theclimb profile is continued. The flaps are raised at thebeginning of the acceleration segment and power ismaintained at the takeoff setting as long as possible(5 minutes maximum).

FOURTH OR FINAL SEGMENTThis segment is from the 400 to 1,500-foot AGL alti-tude with power set at maximum continuous. Therequired climb in this segment is a gradient of 1.2 per-cent for two-engine airplanes, 1.55 for three-engine air-planes, and 1.7 percent for four-engine airplanes.

SECOND SEGMENT CLIMB LIMITATIONSThe second segment climb requirements, from 35 to400 feet, are the most restrictive (or hardest to meet) ofthe climb segments. The pilot must determine that thesecond segment climb is met for each takeoff. In orderto achieve this performance at the higher density alti-tude conditions, it may be necessary to limit the takeoffweight of the airplane.

Landing Gear

Engine

Air Speed

Flaps

Power

Down Retraction Retracted

Retracted

AllOperating One Inoperative

Vfs or1.25 VS Min.

Variable VariableV2

VLOFVRV1

V2

Down

Takeoff M.C.

400'

1500

'

35'

Items 1st. T/OSegment

2nd. T/OSegment

Transition(Acceleration)

Final T/OSegment

2 Engine3 Engine4 Engine

Positive3.0%5.0%

PositivePositivePositive

2.4%2.7%3.0%

1.2%1.5%1.7%

Wing Flaps

Landing Gear

Engines

Power

Air Speed

T.O.

Down

1 Out

T.O.

VLOF V2

T.O.

Up

1 Out

T.O.

V2

T.O.

Up

1 Out

T.O.V2 1.25 VS

(Min)

Up

Up

1 Out

M.C.

1.25 VS (Min)

*

* Required Absolute Minimum Gradient of Flight Path

M.C. = Maximum Continuous

V1 = Critical-Engine-Failure Speed

V2 = Takeoff Safety Speed

VS = Calibrated Stalling Speed, or min.

steady flight speed at which the

airplane is controllable

VR = Speed at which airplane can start

safely raising nose wheel off surface

(Rotational Speed)

VLOF = Speed at point where airplane lifts off

Ground Roll

1st. Segment Climb

2nd. Segment Climb

3rd. orAcceleration

Final or 4thSegment

Climb

Figure 9-38. One-engine inoperative takeoff flightpath.

Ch 09.qxd 10/24/03 7:24 AM Page 9-35

9-36

It must be realized that, regardless of the actualavailable length of the takeoff runway, takeoffweight must be adjusted so that the second segmentclimb requirements can be met. The airplane maywell be capable of lifting off with one engine inoper-ative, but it must then be able to climb and clearobstacles. Although second segment climb may notpresent much of a problem at the lower altitudes, atthe higher altitude airports and higher temperaturesthe second segment climb chart should be consultedto determine the effects on maximum takeoffweights before figuring takeoff runway distancerequired.

AIR CARRIER OBSTACLECLEARANCE REQUIREMENTSRegulations require that large transport category tur-bine powered airplanes certificated after September 30,1958, be taken off at a weight that allows a net takeoffflightpath (one engine inoperative) that clears all obstacleseither by a height of at least 35 feet vertically, or by at least200 feet horizontally within the airport boundaries and byat least 300 feet horizontally after passing the boundaries.The takeoff flightpath is considered to begin 35 feet abovethe takeoff surface at the end of the takeoff distance, andextends to a point in the takeoff at which the airplane is1,500 feet above the takeoff surface, or at which thetransition from the takeoff to the enroute configuration iscompleted. The net takeoff flightpath is the actual takeoffflightpath reduced at each point by 0.8 percent for two-engine airplanes, 0.9 percent for three-engine airplanes,and 1.0 percent for four-engine airplanes.

Air carrier pilots therefore are responsible not only fordetermining that there is enough runway available foran engine inoperative takeoff (balanced field length),and the ability to meet required climb gradients; but

they must also assure that the airplane will be able tosafely clear any obstacles that may be in the takeoffflightpath.

The net takeoff flightpath and obstacle clearancerequired are shown in figure 9-39.

The usual method of computing net takeoff flightpathperformance is to add up the total ground distancesrequired for each of the climb segments and/or useobstacle clearance performance charts in the AFM.Although this obstacle clearance requirement is seldoma limitation at the normally used airports, it is quiteoften an important consideration under critical condi-tions such as high takeoff weight and/or high-densityaltitude. Consider that at a 2.4 percent climb gradient(2.4 feet up for every 100 feet forward) a 1,500-footaltitude gain would take a horizontal distance of 10.4nautical miles to achieve.

SUMMARY OF TAKEOFF REQUIREMENTSIn order to establish the allowable takeoff weight for atransport category airplane, at any airfield, the follow-ing must be considered:

• Airfield pressure altitude

• Temperature

• Headwind component

• Runway length

• Runway gradient or slope

• Obstacles in the flightpath

Once the above details are known and applied to theappropriate performance charts, it is possible to deter-mine the maximum allowable takeoff weight. This

400'

35'

35'

Minimum Actual Takeoff Flight Path

Net Takeoff Flight Path

Obstacle Clearance Path

35'

Figure 9-39.Takeoff obstacle clearance requirements.

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weight would be the lower of the maximum weights asallowed by:

• Balanced field length required

• Engine inoperative climb ability (second segmentlimited)

• Obstacle clearance requirement

In practice, restrictions to takeoff weight at low altitudeairports are usually due to runway length limitations;engine inoperative climb limitations are most commonat the higher altitude airports. All limitations to weightmust be observed. Since the combined weight of fueland payload in the airplane may amount to nearly halfthe maximum takeoff weight, it is usually possible toreduce fuel weight to meet takeoff limitations. If this isdone, however, flight planning must be recalculated inlight of reduced fuel and range.

LANDING PERFORMANCEAs in the takeoff planning, certain speeds must be con-sidered during landing. These speeds are shown below.

LEVEL CONDITION

PLANNING THE LANDINGAs in the takeoff, the landing speeds shown aboveshould be precomputed and visible to both pilots priorto the landing. The VREF speed, or threshold speed, isused as a reference speed throughout the traffic patternor instrument approach as in the following example:

VREF plus 30K .......Downwind or procedure turn

VREF plus 20K .......Base leg or final course inbound tofinal fix

VREF plus 10K .......Final or final course inbound from fix (ILS final)

VREF .......................Speed at the 50-foot height above the threshold

LANDING REQUIREMENTSThe maximum landing weight of an airplane can berestricted by either the approach climb requirements orby the landing runway available.

APPROACH CLIMB REQUIREMENTSThe approach climb is usually more limiting (or moredifficult to meet) than the landing climb, primarilybecause it is based upon the ability to execute a missedapproach with one engine inoperative. The requiredclimb gradient can be affected by pressure altitude andtemperature and, as in the second segment climb in thetakeoff, airplane weight must be limited as needed inorder to comply with this climb requirement.

LANDING RUNWAY REQUIREDThe runway distance needed for landing can beaffected by the following:

• Pressure altitude

• Temperature

• Headwind component

• Runway gradient or slope

• Airplane weight

In computing the landing distance required, some man-ufacturers do not include all of the above items in theircharts, since the regulations state that only pressurealtitude, wind, and airplane weight must be considered.Charts are provided for anti-skid on and anti-skid offconditions, but the use of reverse thrust is not used incomputing required landing distances.

The landing distance, as required by the regulations, isthat distance needed to land and come to a completestop from a point 50 feet above the threshold end of therunway. It includes the air distance required to travelfrom the 50-foot height to touchdown (which can con-sume 1,000 feet of runway distance), plus the stopping

Speed Definition

VSO Stalling speed or the minimum steady flight speed in the landing configuration.

VREF 1.3 times the stalling speed in the landing configuration. This is the required speed at the 50-foot height above the threshold end of the run-way.

The approach climb speed is the speed which would give the best climb performance in the approach configuration, with one engine inop-erative, and with maximum takeoff power on the operating engine(s). The required gradient of climb in thisconfiguration is 2.1 percent for two-engine airplanes, 2.4 percent for three-engine airplanes, and 2.7 per-cent for four-engine airplanes.

This speed would give the best per-formance in the full landing configu-ration with maximum takeoff power on all engines. The gradient of climb required in this configuration is 3.2 percent.

ApproachClimb

LandingClimb

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distance, with no margin left over. This is all that isrequired for 14 CFR part 91 operators (non-air carrier),and all that is shown on some landing distance requiredcharts.

For air carriers and other commercial operators sub-jected to 14 CFR part 121, a different set of rulesapplies which states that the required landing distancefrom the 50-foot height cannot exceed 60 percent ofthe actual runway length available. In all cases, theminimum airspeed allowed at the 50-foot height mustbe no less than 1.3 times the airplane’s stalling speed inthe landing configuration. This speed is commonlycalled the airplane’s VREF speed and will vary withlanding weight. Figure 9-40 is a diagram of these land-ing runway requirements.

SUMMARY OF LANDING REQUIREMENTSIn order to establish the allowable landing weight for atransport category airplane, the following details mustbe considered:

• Airfield pressure altitude

• Temperature

• Headwind component

• Runway length

• Runway gradient or slope

• Runway surface condition

With these details, it is possible to establish the maxi-mum allowable landing weight, which will be thelower of the weights as dictated by:

• Landing runway requirements

• Approach climb requirements

In practice, the approach climb limitations (ability toclimb in approach configuration with one engineinoperative) are seldom encountered because thelanding weights upon arrival at the destination airportare usually light. However, as in the second segmentclimb requirement for takeoff, this approach climbgradient must be met and landing weights must berestricted if necessary. The most likely conditions thatwould make the approach climb critical would be thelandings at high weights and high-pressure altitudesand temperatures, which might be encountered if alanding were required shortly after takeoff.

Landing field requirements can more frequently limitan airplane’s allowable landing weight than theapproach climb limitations. Again, however, unless therunway is particularly short, this is seldom problemat-ical as the average landing weight at the destinationseldom approaches the maximum design landingweight due to fuel burn off.

CompleteStop

Required Landing Distance 14 CFR part 91 40% of Runway Length

Required Landing Runway Length 14 CFR part 121

50'

1.3 VS0

VS0 Approach

Figure 9-40. Landing runway requirements.

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EXAMPLES OF PERFORMANCE CHARTS

Figures 9-41 through 9-62 are examples of charts used for transport category airplanes.

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Figure 9-41. Minimum takeoff power at 1700 r.p.m.

Figure 9-42.Takeoff distance—Flaps takeoff.

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Figure 9-43. Accelerate stop—Flaps takeoff.

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Figure 9-44. Climb – Two engines—Flaps up.

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Figure 9-45.Time, fuel, and distance to cruise climb.

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Figure 9-46. Climb—One engine inoperative.

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Figure 9-47. Service ceiling—One engine inoperative.

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Figure 9-48. Recommended cruise power—ISA +10º C

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Figure 9-49.Time, fuel, and distance to descend.

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Figure 9-50. Normal landing distance—Flaps landing.

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9-49

Figure 9-51. DC-9—Takeoff speeds.

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9-50

Figure 9-52. Long range climb schedule.

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Figure 9-53. Alternate planning chart.

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Figure 9-54. B-737—Takeoff performance.

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Figure 9-55. En route climb 280/.70 ISA.

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Figure 9-56. B-737—Flight planning .78 mach indicated.

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Figure 9-57. Drift-down performance chart.

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Figure 9-58. Landing performance chart.

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9-57

Figure 9-59.Takeoff performance.

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Figure 9-60. Descent performance chart.

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Figure 9-61. B-727—Normal landing distance comparison.

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Figure 9-62. B-727—Landing thrust—140,000 pounds.

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Whether preparing for a local flight or a long cross-country, flight-planning decisions based onweather can dramatically affect the safety of the flight.A solid understanding of weather theory provides thetools necessary to understand the reports and forecastsobtained from a Flight Service Station weather specialist and other aviation weather services.

This chapter is designed to help pilots acquire the background knowledge of weather principles necessaryto develop sound decision making skills relating toweather. It is important to note, however, that there isno substitute for experience.

NATURE OF THE ATMOSPHEREThe atmosphere is a mixture of gases that surround theEarth. This blanket of gases provides protection fromultraviolet rays as well as supporting human, animal,and plant life on the planet. Nitrogen accounts for 78percent of the gases that comprise the atmosphere,while oxygen makes up 21 percent. Argon, carbondioxide, and traces of other gases make up the remain-ing 1 percent. [Figure 10-1]

Within this envelope of gases, there are several recognizable layers of the atmosphere that are definednot only by altitude, but also by the specific characteristics of that level. [Figure 10-2]

The first layer, known as the troposphere, extendsfrom sea level up to 20,000 feet (8 km) over the northern and southern poles and up to 48,000 feet (14.5km) over the equatorial regions. The vast majority ofweather, clouds, storms, and temperature variances

1% Trace Gases

21% Oxygen

78% Nitrogen

Figure 10-1. Composition of the atmosphere.

Troposphere—The layer of the atmosphere extending from the surfaceto a height of 20,000 to 60,000 feet depending on latitude.

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occur within this first layer of the atmosphere. Insidethe troposphere, the temperature decreases at a rate ofabout 2° Celsius every 1,000 feet of altitude gain, andthe pressure decreases at a rate of about 1 inch per1,000 feet of altitude gain. At the top of the troposphereis a boundary known as the tropopause, which trapsmoisture, and the associated weather, in the troposphere. The altitude of the tropopause varies withlatitude and with the season of the year; therefore, ittakes on an elliptical shape, as opposed to round.Location of the tropopause is important because it iscommonly associated with the location of the jetstream and possible clear air turbulence.

The atmospheric level above the tropopause is thestratosphere, which extends from the tropopause to aheight of about 160,000 feet (50 km). Little weatherexists in this layer and the air remains stable. At the topof the stratosphere is another boundary known as thestratopause, which exists at approximately 160,000feet. Directly above this is the mesosphere, whichextends to the mesopause boundary at about 280,000feet (85 km). The temperature in the mesospheredecreases rapidly with an increase in altitude and canbe as cold as –90°C. The last layer of the atmosphere isthe thermosphere. It starts above the mesosphere andgradually fades into outer space.

OXYGEN AND THE HUMAN BODYAs discussed earlier, nitrogen and other trace gasesmake up 79 percent of the atmosphere, while theremaining 21 percent is life sustaining, atmosphericoxygen. At sea level, atmospheric pressure is greatenough to support normal growth, activity, and life. At18,000 feet, however, the partial pressure of oxygen issignificantly reduced to the point that it adverselyaffects the normal activities and functioning of thehuman body. In fact, the reactions of the average person begin to be impaired at an altitude of about10,000 feet and for some people as low as 5,000 feet.The physiological reactions to oxygen deprivation areinsidious and affect people in different ways. Thesesymptoms range from mild disorientation to total incapacitation, depending on body tolerance and altitude.

Thermosphere

Mesosphere

Mesopause

Stratopause

Stratosphere

Troposphere

Tropopause

Figure 10-2. Layers of the atmosphere.

Tropopause—The boundary between the troposphere and the stratosphere which acts as a lid to confine most of the water vapor, andthe associated weather, to the troposphere.

Jetstream—A narrow band of wind with speeds of 100 to 200 m.p.h.usually associated with the tropopause.

Stratosphere—A layer of the atmosphere above the tropopause extending to a height of approximately 160,000 feet.

Mesosphere—A layer of the atmosphere directly above the stratosphere.

Thermosphere—The last layer of the atmosphere that begins above themesosphere and gradually fades away into space.

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By using supplemental oxygen or cabin pressurizationsystems, pilots can fly at higher altitudes and overcomethe ill effects of oxygen deprivation.

SIGNIFICANCE OF ATMOSPHERIC PRESSUREAt sea level, the atmosphere exerts pressure on theEarth at a force of 14.7 pounds per square inch. Thismeans a column of air 1-inch square, extending fromthe surface up to the upper atmospheric limit, weighsabout 14.7 pounds. [Figure 10-3] A person standing atsea level also experiences the pressure of the atmosphere; however, the pressure is not a downwardforce, but rather a force of pressure over the entire surface of the skin.

The actual pressure at a given place and time will differwith altitude, temperature, and density of the air. Theseconditions also affect aircraft performance, especiallywith regard to takeoff, rate of climb, and landings.

MEASUREMENT OF ATMOSPHERIC PRESSUREAtmospheric pressure is typically measured in inchesof mercury (in. Hg.) by a mercurial barometer. [Figure10-4] The barometer measures the height of a columnof mercury inside a glass tube. A section of the mercuryis exposed to the pressure of the atmosphere, whichexerts a force on the mercury. An increase in pressureforces the mercury to rise inside the tube; as pressuredrops, mercury drains out of the tube, decreasing theheight of the column. This type of barometer is typically used in a lab or weather observation station, isnot easily transported, and is a bit difficult to read.

An aneroid barometer is an alternative to a mercurialbarometer; it is easier to read and transport. [Figure 10-5] The aneroid barometer contains a closed vessel,called an aneroid cell, that contracts or expands withchanges in pressure. The aneroid cell attaches to a pressure indicator with a mechanical linkage to providepressure readings. The pressure sensing part of an aircraft altimeter is essentially an aneroid barometer. Itis important to note that due to the linkage mechanismof an aneroid barometer, it is not as accurate as a mercurial barometer.

14.7 lbs.

Area =1Square Inch

Figure 10-3. One square inch of atmosphere weighs approximately 14.7 pounds.

At sea level in astandard atmosphere,the weight of theatmosphere supportsa column of mercury29.92 inches high.

Heightof

Barometer29.92 inches

(760 mm)

Atmospheric Pressure

SeaLevel

29.92 in. Hg. = 1013.2 mb (hPa) = 14.7 lbs./in2

Figure 10-4. Mercurial barometer.

Figure 10-5. Aneroid barometer.

Lower

Higher

SealedAneroid

Cell

AtmosphericPressure

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To provide a common reference for temperature andpressure the International Standard Atmosphere (ISA)has been established. These standard conditions are thebasis for certain flight instruments and most airplaneperformance data. Standard sea level pressure isdefined as 29.92 in. Hg. at 59°F (15°C). Atmosphericpressure is also reported in millibars, with 1 inch ofmercury equaling approximately 34 millibars and standard sea level equaling 1013.2 millibars. Typicalmillibar pressure readings range from 950.0 to 1040.0millibars. Constant pressure charts and hurricane pressure reports are written using millibars.

Since weather stations are located around the globe, alllocal barometric pressure readings are converted to asea level pressure to provide a standard for records andreports. To achieve this, each station converts its barometric pressure by adding approximately 1 inch ofmercury for every 1,000 feet of elevation gain. Forexample, a station at 5,000 feet above sea level, with areading of 24.92 inches of mercury, reports a sea levelpressure reading of 29.92 inches. [Figure 10-6] Usingcommon sea level pressure readings helps ensure aircraft altimeters are set correctly, based on the currentpressure readings.

By tracking barometric pressure trends across a largearea, weather forecasters can more accurately predictmovement of pressure systems and the associatedweather. For example, tracking a pattern of rising pressure at a single weather station generally indicatesthe approach of fair weather. Conversely, decreasing orrapidly falling pressure usually indicates approachingbad weather and possibly, severe storms.

EFFECT OF ALTITUDE ON ATMOSPHERICPRESSUREAs altitude increases, pressure diminishes, as theweight of the air column decreases. On average, withevery 1,000 feet of altitude increase, the atmosphericpressure decreases 1 inch of mercury. This decrease inpressure (increase in density altitude) has a pronouncedeffect on aircraft performance.

EFFECT OF ALTITUDE ON FLIGHTAltitude affects every aspect of flight from aircraft performance to human performance. At higher altitudes, with a decreased atmospheric pressure, takeoff and landing distances are increased, as areclimb rates.

When an aircraft takes off, lift must be developed bythe flow of air around the wings. If the air is thin, morespeed is required to obtain enough lift for takeoff;therefore, the ground run is longer. An aircraft thatrequires a 1,000-foot ground run at sea level willrequire almost double that at an airport 5,000 feetabove sea level [Figure 10-7]. It is also true that athigher altitudes, due to the decreased density of the air,aircraft engines and propellers are less efficient. Thisleads to reduced rates of climb and a greater ground runfor obstacle clearance.

Station Pressure (New Orleans) 29.92"

Standard Atmosphere

Station Pressure(Denver) 24.92"

New Orleans 29.92"Sea Level PressureDenver 29.92"

Figure 10-6. Station pressure is converted to, and reported in, sea level pressure.

ISA—International Standard Atmosphere: Standard atmosphericconditions consisting of a temperature of 59°F (15°C), and a baromet-ric pressure of 29.92 in. Hg. (1013.2 mb) at sea level. ISA values canbe calculated for various altitudes using standard lapse rate.

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EFFECT OF DIFFERENCES IN AIR DENSITYDifferences in air density caused by changes in temperature result in changes in pressure. This, in turn, creates motion in the atmosphere, both vertically andhorizontally, in the form of currents and wind. Motionin the atmosphere, combined with moisture, producesclouds and precipitation otherwise known as weather.

WINDPressure and temperature changes produce two kindsof motion in the atmosphere—vertical movement ofascending and descending currents, and horizontalmovement in the form of wind. Both types of motion inthe atmosphere are important as they affect the takeoff,landing, and cruise flight operations. More important, however, is that these motions in the atmosphere, otherwise called atmospheric circulation,cause weather changes.

THE CAUSE OF ATMOSPHERIC CIRCULATIONAtmospheric circulation is the movement of air aroundthe surface of the Earth. It is caused by uneven heatingof the Earth’s surface and upsets the equilibrium of theatmosphere, creating changes in air movement andatmospheric pressure. Because the Earth has a curved

surface that rotates on a tilted axis while orbiting thesun, the equatorial regions of the Earth receive a greateramount of heat from the sun than the polar regions. Theamount of sun that heats the Earth depends upon thetime of day, time of year, and the latitude of the specificregion. All of these factors affect the length of time andthe angle at which sunlight strikes the surface.

In general circulation theory, areas of low pressureexist over the equatorial regions, and areas of highpressure exist over the polar regions due to a differencein temperature. Solar heating causes air to become lessdense and rise in equatorial areas. The resulting lowpressure allows the high-pressure air at the poles toflow along the planet’s surface toward the equator. Asthe warm air flows toward the poles, it cools, becomingmore dense, and sinks back toward the surface. [Figure10-8] This pattern of air circulation is correct in theory;however, the circulation of air is modified by severalforces, most importantly the rotation of the Earth.

The force created by the rotation of the Earth is knownas Coriolis force. This force is not perceptible to us aswe walk around because we move so slowly and travelrelatively short distances compared to the size and rotation rate of the Earth. However, it does significantlyaffect bodies that move over great distances, such as an

TAKEOFF DISTANCE

0°C0°CPRESS

ALTFT

PRESSALTFT

GRNDROLL

FT

GRNDROLL

FT

TOTAL FTTO CLEAR50 FT OBS

TOTAL FTTO CLEAR50 FT OBS

5000 1185 2125 6000 1305 2360 7000 1440 2635 8000 1590 2960

S.L. 745 1320 1000 815 1445 2000 895 1585 3000 980 1740 4000 1075 1920

1590 ft.

745 ft.

Pressure Altitude:8,000 ft.

Pressure Altitude:Sea Level

Figure 10-7.Takeoff distance increases with increased altitude.

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air mass or body of water. The Coriolis force deflectsair to the right in the Northern Hemisphere, causing itto follow a curved path instead of a straight line. Theamount of deflection differs depending on the latitude.It is greatest at the poles, and diminishes to zero at theequator. The magnitude of Coriolis force also differswith the speed of the moving body—the faster thespeed, the greater the deviation. In the NorthernHemisphere, the rotation of the Earth deflects movingair to the right and changes the general circulation pattern of the air.

The speed of the Earth’s rotation causes the generalflow to break up into three distinct cells in each hemisphere. [Figure 10-9] In the Northern Hemisphere,the warm air at the equator rises upward from the surface, travels northward, and is deflected eastwardby the rotation of the Earth. By the time it has traveledone-third of the distance from the equator to the NorthPole, it is no longer moving northward, but eastward.This air cools and sinks in a belt-like area at about 30°latitude, creating an area of high pressure as it sinkstoward the surface. Then it flows southward along thesurface back toward the equator. Coriolis force bendsthe flow to the right, thus creating the northeasterlytrade winds that prevail from 30° latitude to the equator. Similar forces create circulation cells thatencircle the Earth between 30° and 60° latitude, andbetween 60° and the poles. This circulation patternresults in the prevailing westerly winds in the conterminous United States.

Circulation patterns are further complicated by seasonal changes, differences between the surfaces ofcontinents and oceans, and other factors.

Frictional forces caused by the topography of theEarth’s surface modify the movement of the air in theatmosphere. Within 2,000 feet of the ground, the friction between the surface and the atmosphere slowsthe moving air. The wind is diverted from its pathbecause the frictional force reduces the Coriolis force.This is why the wind direction at the surface variessomewhat from the wind direction just a few thousandfeet above the Earth.

WIND PATTERNSAir flows from areas of high pressure into those of lowpressure because air always seeks out lower pressure.In the Northern Hemisphere, this flow of air from areasof high to low pressure is deflected to the right; producing a clockwise circulation around an area ofhigh pressure. This is also known as anti-cyclonic circulation. The opposite is true of low-pressure areas;the air flows toward a low and is deflected to create acounter-clockwise or cyclonic circulation. [Figure 10-10]

High-pressure systems are generally areas of dry, stable, descending air. Good weather is typically associated with high-pressure systems for this reason.Conversely, air flows into a low-pressure area toreplace rising air. This air tends to be unstable, and usually brings increasing cloudiness and precipitation.Thus, bad weather is commonly associated with areasof low pressure.

A good understanding of high- and low-pressure windpatterns can be of great help when planning a flight,because a pilot can take advantage of beneficial tailwinds. [Figure 10-11] When planning a flight fromwest to east, favorable winds would be encountered

Surface Flow

Equator

Figure 10-8. Circulation pattern in a static environment.

60° N

30° N

60° S

30° S

0°

Figure 10-9. Three-cell circulation pattern due to the rotationof the Earth.

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along the northern side of a high-pressure system or thesouthern side of a low-pressure system. On the returnflight, the most favorable winds would be along thesouthern side of the same high-pressure system or thenorthern side of a low-pressure system. An addedadvantage is a better understanding of what type ofweather to expect in a given area along a route of flightbased on the prevailing areas of highs and lows.

The theory of circulation and wind patterns is accuratefor large-scale atmospheric circulation; however, itdoes not take into account changes to the circulation ona local scale. Local conditions, geological features, andother anomalies can change the wind direction andspeed close to the Earth’s surface.

CONVECTIVE CURRENTSDifferent surfaces radiate heat in varying amounts.Plowed ground, rocks, sand, and barren land give off alarge amount of heat; water, trees, and other areas ofvegetation tend to absorb and retain heat. The resultinguneven heating of the air creates small areas of localcirculation called convective currents.

Convective currents cause the bumpy, turbulent airsometimes experienced when flying at lower altitudesduring warmer weather. On a low altitude flight overvarying surfaces, updrafts are likely to occur over pavement or barren places, and downdrafts often occurover water or expansive areas of vegetation like agroup of trees. Typically, these turbulent conditions canbe avoided by flying at higher altitudes, even abovecumulus cloud layers. [Figure 10-12]

Convective currents are particularly noticeable in areaswith a landmass directly adjacent to a large body ofwater, such as an ocean, large lake, or other appreciablearea of water. During the day, land heats faster thanwater, so the air over the land becomes warmer and lessdense. It rises and is replaced by cooler, denser airflowing in from over the water. This causes an onshorewind, called a sea breeze. Conversely, at night landcools faster than water, as does the corresponding air.In this case, the warmer air over the water rises and isreplaced by the cooler, denser air from the land,creating an offshore wind called a land breeze. Thisreverses the local wind circulation pattern. Convectivecurrents can occur anywhere there is an uneven heatingof the Earth’s surface. [Figure 10-13]

High

Low

Figure 10-10. Circulation pattern about areas of high and lowpressure.

High

Low

Figure 10-11. Favorable winds near a high-pressure system.

Sea Breeze—A coastal breeze blowing from sea to land caused by thetemperature difference when the land surface is warmer than the seasurface. The sea breeze usually occurs during the day.

Land Breeze—A coastal breeze flowing from land to sea caused by thetemperature difference when the sea surface is warmer than the adja-cent land. The land breeze usually occurs at night.

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Convection currents close to the ground can affect apilot’s ability to control the aircraft. On final approach,for example, the rising air from terrain devoid of vegetation sometimes produces a ballooning effect thatcan cause a pilot to overshoot the intended landingspot. On the other hand, an approach over a large bodyof water or an area of thick vegetation tends to create asinking effect that can cause an unwary pilot to landshort of the intended landing spot. [Figure 10-14]

EFFECT OF OBSTRUCTIONS ON WINDAnother atmospheric hazard exists that can create problems for pilots. Obstructions on the ground affectthe flow of wind and can be an unseen danger. Groundtopography and large buildings can break up the flowof the wind and create wind gusts that change rapidlyin direction and speed. These obstructions range frommanmade structures like hangars to large naturalobstructions, such as mountains, bluffs, or canyons. It

10-8

Thermals

Figure 10-12. Convective turbulence avoidance.

Return Flow

Sea BreezeWarm Cool

WarmCool

Return Flow

Land Breeze

Figure 10-13. Sea breeze and land breeze wind circulation patterns.

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is especially important to be vigilant when flying in orout of airports that have large buildings or naturalobstructions located near the runway. [Figure 10-15]

The intensity of the turbulence associated with groundobstructions depends on the size of the obstacle and theprimary velocity of the wind. This can affect the takeoff and landing performance of any aircraft and canpresent a very serious hazard. During the landing phaseof flight, an aircraft may “drop in” due to the turbulentair and be too low to clear obstacles during theapproach.

This same condition is even more noticeable when flying in mountainous regions. [Figure 10-16] Whilethe wind flows smoothly up the windward side of themountain and the upward currents help to carry an aircraft over the peak of the mountain, the wind on theleeward side does not act in a similar manner. As the airflows down the leeward side of the mountain, the airfollows the contour of the terrain and is increasinglyturbulent. This tends to push an aircraft into the side ofa mountain. The stronger the wind, the greater thedownward pressure and turbulence become.

Due to the effect terrain has on the wind in valleys orcanyons, downdrafts can be severe. Thus, a prudentpilot is well advised to seek out a mountain qualifiedflight instructor and get a mountain checkout beforeconducting a flight in or near mountainous terrain.

LOW-LEVEL WIND SHEARWind shear is a sudden, drastic change in windspeedand/or direction over a very small area. Wind shear cansubject an aircraft to violent updrafts and downdraftsas well as abrupt changes to the horizontal movementof the aircraft. While wind shear can occur at any altitude, low-level wind shear is especially hazardousdue to the proximity of an aircraft to the ground.Directional wind changes of 180° and speed changes of50 knots or more are associated with low-level windshear. Low-level wind shear is commonly associatedwith passing frontal systems, thunderstorms, and temperature inversions with strong upper level winds(greater than 25 knots).

Wind shear is dangerous to an aircraft for several reasons. The rapid changes in wind direction and velocity changes the wind’s relation to the aircraft disrupting the normal flight attitude and performanceof the aircraft. During a wind shear situation, the effectscan be subtle or very dramatic depending on windspeedand direction of change. For example, a tailwind thatquickly changes to a headwind will cause an increasein airspeed and performance. Conversely, when a headwind changes to a tailwind, the airspeed will rapidly decrease and there will be a correspondingdecrease in performance. In either case, a pilot must beprepared to react immediately to the changes to maintain control of the aircraft.

Figure 10-14. Currents generated by varying surface conditions.

CoolSinking

Air

Intended Flight Path

WarmRising

Air

Wind ShearA sudden, drastic shift in windspeed, direction, or boththat may occur in the horizontal or vertical plane.

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In general, the most severe type of low-level windshear is associated with convective precipitation or rainfrom thunderstorms. One critical type of shear associated with convective precipitation is known as amicroburst. A typical microburst occurs in a space ofless than 1 mile horizontally and within 1,000 feet vertically. The lifespan of a microburst is about 15 minutes during which it can produce downdrafts of upto 6,000 feet per minute. It can also produce a hazardous wind direction change of 45 knots or more,in a matter of seconds. When encountered close to theground, these excessive downdrafts and rapid changes

in wind direction can produce a situation in which it isdifficult to control the aircraft. [Figure 10-17] Duringan inadvertent takeoff into a microburst, the plane firstexperiences a performance-increasing headwind (#1),followed by performance-decreasing downdrafts (#2).Then the wind rapidly shears to a tailwind (#3), and canresult in terrain impact or flight dangerously close tothe ground (#4).

Figure 10-15.Turbulence caused by manmade obstructions.

Figure 10-16.Turbulence encountered over and around mountainous regions.

WIND

MicroburstΑ strong downdraft which normally occurs over horizontaldistances of 1 NM or less and vertical distances of less than 1,000 feet. Inspite of its small horizontal scale, an intense microburst could inducewindspeeds greater than 100 knots and downdrafts as strong as 6,000feet per minute.

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Microbursts are often difficult to detect because theyoccur in a relatively confined area. In an effort to warnpilots of low-level wind shear, alert systems have beeninstalled at several airports around the country. A seriesof anemometers, placed around the airport, form a netto detect changes in windspeeds. When windspeedsdiffer by more than 15 knots, a warning for wind shearis given to pilots. This system is known as the low-levelwind shear alert system, or LLWAS.

It is important to remember that wind shear can affectany flight and any pilot at any altitude. While windshear may be reported, it often remains undetected andis a silent danger to aviation. Always be alert to the possibility of wind shear, especially when flying in andaround thunderstorms and frontal systems.

WIND AND PRESSURE REPRESENTATIONON SURFACE WEATHER MAPSSurface weather maps provide information aboutfronts, areas of high and low pressure, and surfacewinds and pressures for each station. This type ofweather map allows pilots to see the locations of frontsand pressure systems, but more importantly, it depictsthe wind and pressure at the surface for each location.For more information on surface analysis and weatherdepiction charts see Chapter 11.

Wind conditions are reported by an arrow attached tothe station location circle. [Figure 10-18] The stationcircle represents the head of the arrow, with the arrowpointing in the direction from which the wind is blowing. Winds are described by the direction fromwhich they blow, thus a northwest wind means that thewind is blowing from the northwest toward the southeast. The speed of the wind is depicted by barbs

or pennants placed on the wind line. Each barb represents a speed of 10 knots, while half a barb isequal to 5 knots and a pennant is equal to 50 knots.

The pressure for each station is recorded on the weatherchart and is shown in millibars. Isobars are lines drawnon the chart to depict areas of equal pressure. Theselines result in a pattern that reveals the pressure gradient or change in pressure over distance. [Figure10-19] Isobars are similar to contour lines on a topographic map that indicate terrain altitudes andslope steepness. For example, isobars that are closelyspaced indicate a steep wind gradient and strong windsprevail. Shallow gradients, on the other hand, are represented by isobars that are spaced far apart, and areindicative of light winds. Isobars help identify low- andhigh-pressure systems as well as the location of ridges,troughs, and cols. A high is an area of high pressure

Strong Downdraft

Increasing Headwind Increasing Tailwind

Outflow Outflow

1

2

34

Figure 10-17. Effect of a microburst wind.

NW / 5 kts SW / 20 kts

E / 35 kts N / 50 kts W / 105 kts

Calm

Examples of wind speed and direction plots

Figure 10-18. Depiction of winds on a surface weather chart.

Isobars—Lines which connect points of equal barometric pressure.

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surrounded by lower pressure; a low is an area of lowpressure surrounded by higher pressure. A ridge is anelongated area of high pressure, and a trough is an elongated area of low pressure. A col is the intersectionbetween a ridge and a trough, or an area of neutralitybetween two highs or two lows.

Isobars furnish valuable information about winds in thefirst few thousand feet above the surface. Close to theground, wind direction is modified by the surface andwindspeed decreases due to friction with the surface. At levels 2,000 to 3,000 feet above the surface, however, the speed is greater and the directionbecomes more parallel to the isobars. Therefore, thesurface winds are shown on the weather map as well asthe winds at a slightly higher altitude.

Generally, the wind 2,000 feet above the ground will be20° to 40° to the right of surface winds, and the wind-speed will be greater. The change of wind direction isgreatest over rough terrain and least over flat surfaces,such as open water. In the absence of winds aloft information, this rule of thumb allows for a rough estimate of the wind conditions a few thousand feetabove the surface.

ATMOSPHERIC STABILITYThe stability of the atmosphere depends on its ability toresist vertical motion. A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear. In an unstableatmosphere, small vertical air movements tend tobecome larger, resulting in turbulent airflow and convective activity. Instability can lead to significantturbulence, extensive vertical clouds, and severeweather.

Rising air expands and cools due to the decrease in airpressure as altitude increases. The opposite is true ofdescending air; as atmospheric pressure increases, thetemperature of descending air increases as it is compressed. Adiabatic heating, or adiabatic cooling,are the terms used to describe this temperature change.

The adiabatic process takes place in all upward anddownward moving air. When air rises into an area oflower pressure, it expands to a larger volume. As themolecules of air expand, the temperature of the air lowers. As a result, when a parcel of air rises, pressuredecreases, volume increases, and temperaturedecreases. When air descends, the opposite is true. Therate at which temperature decreases with an increase inaltitude is referred to as its lapse rate. As air ascendsthrough the atmosphere, the average rate of temperature change is 2°C (3.5°F) per 1,000 feet.

Since water vapor is lighter than air, moisture decreasesair density, causing it to rise. Conversely, as moisturedecreases, air becomes denser and tends to sink. Sincemoist air cools at a slower rate, it is generally less sta-ble than dry air since the moist air must rise higherbefore its temperature cools to that of the surroundingair. The dry adiabatic lapse rate (unsaturated air) is 3°C(5.4°F) per 1,000 feet. The moist adiabatic lapse ratevaries from 1.1°C to 2.8°C (2°F to 5°F) per 1,000 feet.

The combination of moisture and temperature determine the stability of the air and the resultingweather. Cool, dry air is very stable and resists verticalmovement, which leads to good and generally clearweather. The greatest instability occurs when the air ismoist and warm, as it is in the tropical regions in thesummer. Typically, thunderstorms appear on a dailybasis in these regions due to the instability of the surrounding air.

Isobars

Closely spaced isobars meana steep pressure gradient andstrong winds.

552

558

564

570

576

582

Widely spaced isobarsmean a shallow pressuregradient and relativelylight winds.

Figure 10-19. Isobars reveal the pressure gradient of an areaof high- or low-pressure areas.

Adiabatic heating—A process of heating dry air through compression.As air moves downward it is compressed, resulting in a temperatureincrease.

Adiabatic cooling—A process of cooling the air through expansion. Forexample, as air moves upward, it expands with the reduction of atmos-pheric pressure and cools as it expands.

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INVERSIONAs air rises and expands in the atmosphere, the temperature decreases. There is an atmospheric anomaly that can occur, however, that changes this typical pattern of atmospheric behavior. When the temperature of the air rises with altitude, a temperatureinversion exists. Inversion layers are commonly shallow layers of smooth, stable air close to the ground.The temperature of the air increases with altitude to acertain point, which is the top of the inversion. The airat the top of the layer acts as a lid, keeping weather andpollutants trapped below. If the relative humidity of theair is high, it can contribute to the formation of clouds,fog, haze, or smoke, resulting in diminished visibilityin the inversion layer.

Surface based temperature inversions occur on clear,cool nights when the air close to the ground is cooledby the lowering temperature of the ground. The airwithin a few hundred feet of the surface becomescooler than the air above it. Frontal inversions occurwhen warm air spreads over a layer of cooler air, orcooler air is forced under a layer of warmer air.

MOISTURE AND TEMPERATUREThe atmosphere, by nature, contains moisture in theform of water vapor. The amount of moisture present inthe atmosphere is dependent upon the temperature ofthe air. Every 20°F increase in temperature doubles theamount of moisture the air can hold. Conversely, adecrease of 20°F cuts the capacity in half.

Water is present in the atmosphere in three states: liquid, solid, and gaseous. All three forms can readilychange to another, and all are present within the temperature ranges of the atmosphere. As waterchanges from one state to another, an exchange of heattakes place. These changes occur through the processesof evaporation, sublimation, condensation, deposition, melting, or freezing. However, water vaporis added into the atmosphere only by the processes ofevaporation and sublimation.

Evaporation is the changing of liquid water to watervapor. As water vapor forms, it absorbs heat from thenearest available source. This heat exchange is knownas the latent heat of evaporation. A good example ofthis is when the body’s perspiration evaporates. The neteffect is a cooling sensation as heat is extracted fromthe body. Similarly, sublimation is the changing of icedirectly to water vapor, completely bypassing the liquid stage. Though dry ice is not made of water, butrather carbon dioxide, it demonstrates the principle ofsublimation, when a solid turns directly into vapor.

RELATIVE HUMIDITYHumidity refers to the amount of water vapor presentin the atmosphere at a given time. Relative humidity is

the actual amount of moisture in the air compared tothe total amount of moisture the air could hold at thattemperature. For example, if the current relativehumidity is 65 percent, the air is holding 65 percent ofthe total amount of moisture that it is capable of holding at that temperature and pressure. While muchof the western United States rarely sees days of highhumidity, relative humidity readings of 75 to 90 percent are not uncommon in the southern UnitedStates during warmer months. [Figure 10-20]

TEMPERATURE/DEWPOINT RELATIONSHIPThe relationship between dewpoint and temperaturedefines the concept of relative humidity. The dewpoint,given in degrees, is the temperature at which the air canhold no more moisture. When the temperature of theair is reduced to the dewpoint, the air is completely saturated and moisture begins to condense out of theair in the form of fog, dew, frost, clouds, rain, hail, orsnow.

As moist, unstable air rises, clouds often form at thealtitude where temperature and dewpoint reach thesame value. When lifted, unsaturated air cools at a rateof 5.4°F per 1,000 feet and the dewpoint temperaturedecreases at a rate of 1°F per 1,000 feet. This results ina convergence of temperature and dewpoint at a rate of4.4°F. Apply the convergence rate to the reported temperature and dewpoint to determine the height ofthe cloud base.

Given:

Temperature (T) = 85°FDewpoint (DP) = 71°FConvergence Rate (CR) = 4.4°T – DP = Temperature Dewpoint Spread (TDS)TDS ÷ CR = X X × 1,000 feet = height of cloud base AGL

Example:

85ºF – 71ºF = 14ºF14ºF ÷ 4.4°F = 3.183.18 × 1,000 = 3,180 feet AGLThe height of the cloud base is 3,180 feet AGL.

Inversion—An increase in temperature with altitude.

Evaporation—The transformation of a liquid to a gaseous state, such asthe change of water to water vapor.

SublimationProcess by which a solid is changed to a gas without goingthrough the liquid state.

CondensationA change of state of water from a gas (water vapor) to aliquid.

DepositionThe direct transformation of a gas to a solid state, in whichthe liquid state is bypassed. Some sources use the term sublimation todescribe this process instead of deposition.

Dewpoint—The temperature at which air reaches a state where it canhold no more water.

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Explanation:

With an outside air temperature (OAT) of 85°F at thesurface, and dewpoint at the surface of 71°F, the spreadis 14°. Divide the temperature dewpoint spread by theconvergence rate of 4.4°F, and multiply by 1,000 todetermine the approximate height of the cloud base.

METHODS BY WHICH AIR REACHES THESATURATION POINTIf air reaches the saturation point while temperatureand dewpoint are close together, it is highly likely thatfog, low clouds, and precipitation will form. There arefour methods by which air can reach the complete saturation point. First, when warm air moves over acold surface, the air’s temperature drops and reachesthe saturation point. Second, the saturation point maybe reached when cold air and warm air mix. Third,when air cools at night through contact with the coolerground, air reaches its saturation point. The fourthmethod occurs when air is lifted or is forced upward inthe atmosphere.

As air rises, it uses heat energy to expand. As a result,the rising air loses heat rapidly. Unsaturated air losesheat at a rate of 3.0°C (5.4°F) for every 1,000 feet of

altitude gain. No matter what causes the air to reach itssaturation point, saturated air brings clouds, rain, andother critical weather situations.

DEW AND FROSTOn cool, calm nights, the temperature of the groundand objects on the surface can cause temperatures ofthe surrounding air to drop below the dewpoint. Whenthis occurs, the moisture in the air condenses anddeposits itself on the ground, buildings, and otherobjects like cars and aircraft. This moisture is known asdew and sometimes can be seen on grass in the morning. If the temperature is below freezing, themoisture will be deposited in the form of frost. Whiledew poses no threat to an aircraft, frost poses a definiteflight safety hazard. Frost disrupts the flow of air overthe wing and can drastically reduce the production oflift. It also increases drag, which, when combined withlowered lift production, can eliminate the ability to takeoff. An aircraft must be thoroughly cleaned and free offrost prior to beginning a flight.

FOGFog, by definition, is a cloud that begins within 50 feetof the surface. It typically occurs when the temperatureof air near the ground is cooled to the air’s dewpoint.

A cubic meter of air with 17g of water vaporat 20°C is at saturation, or 100% relativehumidity. Any further cooling will causecondensation (fog, clouds, dew) to form.Thus, 20°C is the dewpoint for this situation.

If the temperature is loweredto 10°C, the air can only hold9g of water vapor, and 8g ofwater will condense as waterdroplets. The relative humiditywill still be at 100%.

If the same cubic meter of air warmsto 30°C, the 17g of water vapor will produce a relative humidity of 56%.(17g is 56% of the 30g the air could hold at this temperature.)

CCC

Figure 10-20.The relationship between relative humidity, temperature, and dewpoint.

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At this point, water vapor in the air condenses andbecomes visible in the form of fog. Fog is classifiedaccording to the manner in which it forms and isdependent upon the current temperature and theamount of water vapor in the air.

On clear nights, with relatively little to no wind present, radiation fog may develop. [Figure 10-21]Usually, it forms in low-lying areas like mountain valleys. This type of fog occurs when the ground coolsrapidly due to terrestrial radiation, and the surroundingair temperature reaches its dewpoint. As the sun risesand the temperature increases, radiation fog will liftand eventually burn off. Any increase in wind will alsospeed the dissipation of radiation fog. If radiation fog isless than 20 feet thick, it is known as ground fog.

When a layer of warm, moist air moves over a cold surface, advection fog is likely to occur. Unlike radiation fog, wind is required to form advection fog.Winds of up to 15 knots allow the fog to form andintensify; above a speed of 15 knots, the fog usuallylifts and forms low stratus clouds. Advection fog iscommon in coastal areas where sea breezes can blowthe air over cooler landmasses.

In these same coastal areas, upslope fog is likely aswell. Upslope fog occurs when moist, stable air isforced up sloping land features like a mountain range.This type of fog also requires wind for formation andcontinued existence. Upslope and advection fog, unlikeradiation fog, may not burn off with the morning sun,but instead can persist for days. They also can extendto greater heights than radiation fog.

Steam fog, or sea smoke, forms when cold, dry airmoves over warm water. As the water evaporates, itrises and resembles smoke. This type of fog is commonover bodies of water during the coldest times of theyear. Low-level turbulence and icing are commonlyassociated with steam fog.

Ice fog occurs in cold weather when the temperature ismuch below freezing and water vapor forms directlyinto ice crystals. Conditions favorable for its formationare the same as for radiation fog except for cold temperature, usually –25°F or colder. It occurs mostlyin the arctic regions, but is not unknown in middle latitudes during the cold season.

CLOUDSClouds are visible indicators and are often indicative offuture weather. For clouds to form, there must be adequate water vapor and condensation nuclei, as wellas a method by which the air can be cooled. When theair cools and reaches its saturation point, the invisiblewater vapor changes into a visible state. Through theprocesses of deposition (also referred to as sublimation) and condensation, moisture condenses orsublimates onto miniscule particles of matter like dust,salt, and smoke known as condensation nuclei. Thenuclei are important because they provide a means forthe moisture to change from one state to another.

Cloud type is determined by its height, shape, andbehavior. They are classified according to the height oftheir bases as low, middle, or high clouds, as well asclouds with vertical development. [Figure 10-22]

Low clouds are those that form near the Earth’s surfaceand extend up to 6,500 feet AGL. They are made primarily of water droplets, but can include supercooled water droplets that induce hazardous aircraft icing. Typical low clouds are stratus, stratocumulus, and nimbostratus. Fog is also classifiedas a type of low cloud formation. Clouds in this familycreate low ceilings, hamper visibility, and can changerapidly. Because of this, they influence flight planningand can make VFR flight impossible.

Middle clouds form around 6,500 feet AGL and extendup to 20,000 feet AGL. They are composed of water,ice crystals, and supercooled water droplets. Typicalmiddle-level clouds include altostratus and altocumulus. These types of clouds may be encountered on cross-country flights at higher altitudes. Altostratus clouds can produce turbulenceand may contain moderate icing. Altocumulus clouds,which usually form when altostratus clouds are breaking apart, also may contain light turbulence andicing.

Figure 10-21. Radiation fog.

Condensation Nuclei—Small particles of solid matter in the air onwhich water vapor condenses.

Supercooled Water Droplets—Water droplets that have been cooledbelow the freezing point, but are still in a liquid state.

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High clouds form above 20,000 feet AGL and usuallyform only in stable air. They are made up of ice crystalsand pose no real threat of turbulence or aircraft icing.Typical high-level clouds are cirrus, cirrostratus, andcirrocumulus.

Clouds with extensive vertical development are cumulus clouds that build vertically into toweringcumulus or cumulonimbus clouds. The bases of theseclouds form in the low to middle cloud base region butcan extend into high altitude cloud levels. Towering cumulus clouds indicate areas of instability in theatmosphere, and the air around and inside them is turbulent. These types of clouds often developinto cumulonimbus clouds or thunderstorms.Cumulonimbus clouds contain large amounts of moisture and unstable air, and usually produce hazardous weather phenomena such as lightning, hail,tornadoes, gusty winds, and wind shear. These extensive vertical clouds can be obscured by othercloud formations and are not always visible from theground or while in flight. When this happens, theseclouds are said to be embedded, hence the term,embedded thunderstorms.

Cloud classification can be further broken down intospecific cloud types according to the outward

appearance and cloud composition. Knowing theseterms can help identify visible clouds.

The following is a list of cloud classifications:

• Cumulus—Heaped or piled clouds.

• Stratus—Formed in layers.

• Cirrus—Ringlets; fibrous clouds; also high-levelclouds above 20,000 feet.

• Castellanus—Common base with separate vertical development; castle-like.

• Lenticularus—Lens shaped; formed over mountains in strong winds.

• Nimbus—Rain bearing clouds.

• Fracto—Ragged or broken.

• Alto—Meaning high; also middle-level cloudsexisting at 5,000 to 20,000 feet.

To pilots, the cumulonimbus cloud is perhaps the mostdangerous cloud type. It appears individually or ingroups and is known as either an air mass or orographicthunderstorm. Heating of the air near the Earth’s surface creates an air mass thunderstorm; the upslope

Cumulonimbus

Cumulus

Clouds withVertical

Development

Cirrocumulus

Cirrus

Cirrostratus

High Clouds

Middle Clouds

Low Clouds

Stratocumulus

NimbostratusStratus

20,000 AGL

6,500 AGL

Altocumulus

Altostratus

Figure 10-22. Basic cloud types.

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motion of air in the mountainous regions causes orographic thunderstorms. Cumulonimbus clouds thatform in a continuous line are nonfrontal bands of thunderstorms or squall lines.

Since rising air currents cause cumulonimbus clouds,they are extremely turbulent and pose a significant hazard to flight safety. For example, if an aircraft entersa thunderstorm, the aircraft could experience updraftsand downdrafts that exceed 3,000 feet per minute. Inaddition, thunderstorms can produce large hailstones,damaging lightning, tornadoes, and large quantities ofwater, all of which are potentially hazardous to aircraft.

A thunderstorm makes its way through three distinctstages before dissipating. It begins with the cumulusstage, in which lifting action of the air begins. If sufficient moisture and instability are present, theclouds continue to increase in vertical height.Continuous, strong updrafts prohibit moisture fromfalling. The updraft region grows larger than the individual thermals feeding the storm. Within approximately 15 minutes, the thunderstorm reachesthe mature stage, which is the most violent time periodof the thunderstorm’s life cycle. At this point, drops ofmoisture, whether rain or ice, are too heavy for thecloud to support and begin falling in the form of rain orhail. This creates a downward motion of the air. Warm,rising air; cool, precipitation-induced descending air;and violent turbulence all exist within and near thecloud. Below the cloud, the down-rushing air increasessurface winds and decreases the temperature. Once the

vertical motion near the top of the cloud slows down,the top of the cloud spreads out and takes on an anvil-like shape. At this point, the storm enters the dissipating stage. This is when the downdrafts spreadout and replace the updrafts needed to sustain thestorm. [Figure 10-23]

It is impossible to fly over thunderstorms in light aircraft. Severe thunderstorms can punch through thetropopause and reach staggering heights of 50,000 to60,000 feet depending on latitude. Flying under thunderstorms can subject aircraft to rain, hail, damaging lightning, and violent turbulence. A goodrule of thumb is to circumnavigate thunderstorms by atleast 5 nautical miles (NM) since hail may fall for milesoutside of the clouds. If flying around a thunderstormis not an option, stay on the ground until it passes.

CEILINGA ceiling, for aviation purposes, is the lowest layer ofclouds reported as being broken or overcast, or the vertical visibility into an obscuration like fog or haze.Clouds are reported as broken when five-eighths toseven-eighths of the sky is covered with clouds.Overcast means the entire sky is covered with clouds.Current ceiling information is reported by the aviationroutine weather report (METAR) and automatedweather stations of various types.

Ceiling—The height above the Earth’s surface of the lowest layer ofclouds reported as broken or overcast, or the vertical visibility into anobscuration.

40

30

20

10

5

0

Alti

tude

(T

hous

ands

of f

eet)

32°F 0°C

Equilibrium Level

32°F 32°F0°C

3-5 mi.Cumulus Stage

5-10 mi.Mature Stage

5-7 mi.Dissipating Stage

Horizontal Distance

0°C

Figure 10-23. Life cycle of a thunderstorm.

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VISIBILITYClosely related to cloud cover and reported ceilings isvisibility information. Visibility refers to the greatesthorizontal distance at which prominent objects can beviewed with the naked eye. Current visibility is alsoreported in METAR and other aviation weather reports,as well as automated weather stations. Visibility information, as predicted by meteorologists, is available during a preflight weather briefing.

PRECIPITATIONPrecipitation refers to any form of water particles thatform in the atmosphere and fall to the ground. It has aprofound impact on flight safety. Depending on theform of precipitation, it can reduce visibility, createicing situations, and affect landing and takeoff performance of an aircraft.

Precipitation occurs because water or ice particles inclouds grow in size until the atmosphere can no longersupport them. It can occur in several forms as it fallstoward the Earth, including drizzle, rain, ice pellets,hail, and ice.

Drizzle is classified as very small water droplets,smaller than 0.02 inches in diameter. Drizzle usuallyaccompanies fog or low stratus clouds. Water dropletsof larger size are referred to as rain. Rain that fallsthrough the atmosphere but evaporates prior to strikingthe ground is known as virga. Freezing rain and freezing drizzle occur when the temperature of the surface is below freezing; the rain freezes on contactwith the cooler surface.

If rain falls through a temperature inversion, it mayfreeze as it passes through the underlying cold air andfall to the ground in the form of ice pellets. Ice pelletsare an indication of a temperature inversion and thatfreezing rain exists at a higher altitude. In the case ofhail, freezing water droplets are carried up and downby drafts inside clouds, growing larger in size as theycome in contact with more moisture. Once the updraftscan no longer hold the freezing water, it falls to theEarth in the form of hail. Hail can be pea-sized, or itcan grow as large as 5 inches in diameter, larger than asoftball.

Snow is precipitation in the form of ice crystals thatfalls at a steady rate or in snow showers that begin,change in intensity, and end rapidly. Falling snow alsovaries in size, being very small grains or large flakes.Snow grains are the equivalent of drizzle in size.

Precipitation in any form poses a threat to safety offlight. Often, precipitation is accompanied by low ceilings and reduced visibility. Aircraft that have ice,snow, or frost on their surfaces must be carefully

cleaned prior to beginning a flight because of the possible airflow disruption and loss of lift. Rain cancontribute to water in the fuel tanks. Precipitation cancreate hazards on the runway surface itself, makingtakeoffs and landings difficult, if not impossible, due tosnow, ice, or pooling water and very slick surfaces.

AIR MASSESAir masses are large bodies of air that take on the characteristics of the surrounding area, or sourceregion. A source region is typically an area in which theair remains relatively stagnant for a period of days orlonger. During this time of stagnation, the air masstakes on the temperature and moisture characteristicsof the source region. Areas of stagnation can be foundin polar regions, tropical oceans, and dry deserts. Airmasses are classified based on their region of origination:

• Polar or Tropical

• Maritime or Continental

A continental polar air mass forms over a polar regionand brings cool, dry air with it. Maritime tropical airmasses form over warm tropical waters like theCaribbean Sea and bring warm, moist air. As the airmass moves from its source region and passes overland or water, the air mass is subjected to the varyingconditions of the land or water, and these modify thenature of the air mass. [Figure 10-24]

An air mass passing over a warmer surface will bewarmed from below, and convective currents form,causing the air to rise. This creates an unstable air masswith good surface visibility. Moist, unstable air causescumulus clouds, showers, and turbulence to form.Conversely, an air mass passing over a colder surfacedoes not form convective currents, but instead creates astable air mass with poor surface visibility. The poorsurface visibility is due to the fact that smoke, dust, andother particles cannot rise out of the air mass and areinstead trapped near the surface. A stable air mass canproduce low stratus clouds and fog.

FRONTSAs air masses move across bodies of water and land,they eventually come in contact with another air masswith different characteristics. The boundary layerbetween two types of air masses is known as a front.An approaching front of any type always meanschanges to the weather are imminent.

Air Mass—An extensive body of air having fairly uniform properties oftemperature and moisture.

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There are four types of fronts, which are named according to the temperature of the advancing air as itrelates to the temperature of the air it is replacing.[Figure 10-25]

• Warm Front

• Cold Front

• Stationary Front

• Occluded Front

Any discussion of frontal systems must be temperedwith the knowledge that no two fronts are the same.However, generalized weather conditions are associated with a specific type of front that helps identify the front.

WARM FRONTA warm front occurs when a warm mass of airadvances and replaces a body of colder air. Warm frontsmove slowly, typically 10 to 25 miles per hour (m.p.h.).The slope of the advancing front slides over the top ofthe cooler air and gradually pushes it out of the area.Warm fronts contain warm air that often has very highhumidity. As the warm air is lifted, the temperaturedrops and condensation occurs.

Generally, prior to the passage of a warm front, cirriform or stratiform clouds, along with fog, can beexpected to form along the frontal boundary. In the summer months, cumulonimbus clouds (thunderstorms) are likely to develop. Light to moderate precipitation is probable, usually in the formof rain, sleet, snow, or drizzle, punctuated by poor visibility. The wind blows from the south-southeast,and the outside temperature is cool or cold, withincreasing dewpoint. Finally, as the warm frontapproaches, the barometric pressure continues to falluntil the front passes completely.

North American air mass source regions. Note standard air mass abbreviations: arctic (A), continental polar (cP), maritime polar (mP), continental tropical (cT), and maritime tropical (mT).cP

A

mP

mP

mT

mTmT

cT

Figure 10-24. Air mass source regions.

(red/blue)*

Cold Front (blue)*

Symbols for Surface Fronts and Other Significant Lines Shown on the Surface Analysis Chart

Warm Front (red)*

(purple)*

Table A

Occluded Front

Stationary Front

* Note : Fronts may be black and white or color, depending on their source. Also, fronts shown in color code will not necessarily show frontal symbols.

Figure 10-25. Common chart symbology to depict weatherfront location.

Warm Front—The boundary between two air masses where warm air isreplacing cold air.

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During the passage of a warm front, stratiform cloudsare visible and drizzle may be falling. The visibility isgenerally poor, but improves with variable winds. Thetemperature rises steadily from the inflow of relativelywarmer air. For the most part, the dewpoint remainssteady and the pressure levels off.

After the passage of a warm front, stratocumulusclouds predominate and rain showers are possible. Thevisibility eventually improves, but hazy conditions mayexist for a short period after passage. The wind blowsfrom the south-southwest. With warming temperatures,the dewpoint rises and then levels off. There is generally a slight rise in barometric pressure, followedby a decrease of barometric pressure.

FLIGHT TOWARD AN APPROACHING WARMFRONTBy studying a typical warm front, much can be learnedabout the general patterns and atmospheric conditionsthat exist when a warm front is encountered in flight.Figure 10-26 depicts a warm front advancing eastwardfrom St. Louis, Missouri, toward Pittsburgh,Pennsylvania.

At the time of departure from Pittsburgh, the weather isgood VFR with a scattered layer of cirrus clouds at15,000 feet. As the flight progresses westward toColumbus and closer to the oncoming warm front, the

clouds deepen and become increasingly stratiform inappearance with a ceiling of 6,000 feet. The visibilitydecreases to 6 miles in haze with a falling barometricpressure. Approaching Indianapolis, the weather deteriorates to broken clouds at 2,000 feet with 3 milesvisibility and rain. With the temperature and dewpointthe same, fog is likely. At St. Louis, the sky is overcastwith low clouds and drizzle and the visibility is 1 mile.Beyond Indianapolis, the ceiling and visibility wouldbe too low to continue VFR. Therefore, it would bewise to remain in Indianapolis until the warm front hadpassed, which might require a day or two.

COLD FRONTA cold front occurs when a mass of cold, dense, andstable air advances and replaces a body of warmer air.Cold fronts move more rapidly than warm fronts, progressing at a rate of 25 to 30 m.p.h. However,extreme cold fronts have been recorded moving atspeeds of up to 60 m.p.h. A typical cold front moves ina manner opposite that of a warm front; because it is sodense, it stays close to the ground and acts like a snowplow, sliding under the warmer air and forcing theless dense air aloft. The rapidly ascending air causes

COLD AIR

WARM AIR

ST. LOUIS INDIANAPOLIS COLUMBUS PITTSBURGH200 MILES 400 MILES 600 MILES

NIMBOSTRATUS

ALTOSTRATUS

CIRROSTRATUS

CIRRUS

METAR KSTL 1950Z 21018KT 1SM –RA 0VC010 18/18 A2960

METAR KCMH 1950Z 13018KT 6SM HZ 0VC060 14/10 A2990

METAR KPIT 1950Z 13012KT 10SM SCT150 12/01 A3002

METAR KIND 1950Z 16012KT 3SM RA BKN020 15/15 A2973 St. Louis

Indianapolis

1005

1002

999

999 1002 1005 1008 1011 1014

1008 1011 1014 1017

1017

Columbus Pittsburgh

651

1065

593

59 56

606

50

53103420

06802010

40 12526

16618

Figure 10-26. Warm front cross-section with surface weather chart depiction and associated METAR.

Cold Front—The boundary between two air masses where cold air isreplacing warm air.

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the temperature to decrease suddenly, forcing the creation of clouds. The type of clouds that formdepends on the stability of the warmer air mass. A coldfront in the Northern Hemisphere is normally orientedin a northeast to southwest manner and can be several hundred miles long, encompassing a large area of land.

Prior to the passage of a typical cold front, cirriform or towering cumulus clouds are present, and cumulonimbus clouds are possible. Rain showers andhaze are possible due to the rapid development ofclouds. The wind from the south-southwest helps toreplace the warm temperatures with the relative colderair. A high dewpoint and falling barometric pressureare indicative of imminent cold front passage.

As the cold front passes, towering cumulus or cumulonimbus clouds continue to dominate the sky.Depending on the intensity of the cold front, heavy rainshowers form and might be accompanied by lightning,thunder, and/or hail. More severe cold fronts can alsoproduce tornadoes. During cold front passage, the visibility will be poor, with winds variable and gusty,and the temperature and dewpoint drop rapidly. Aquickly falling barometric pressure bottoms out duringfrontal passage, then begins a gradual increase.

After frontal passage, the towering cumulus and cumulonimbus clouds begin to dissipate to cumulusclouds with a corresponding decrease in the precipitation. Good visibility eventually prevails withthe winds from the west-northwest. Temperaturesremain cooler and the barometric pressure continues torise.

FAST-MOVING COLD FRONTFast-moving cold fronts are pushed by intense pressuresystems far behind the actual front. The frictionbetween the ground and the cold front retards themovement of the front and creates a steeper frontal surface. This results in a very narrow band of weather,concentrated along the leading edge of the front. If thewarm air being overtaken by the cold front is relativelystable, overcast skies and rain may occur for some distance ahead of the front. If the warm air is unstable,scattered thunderstorms and rain showers may form. Acontinuous line of thunderstorms, or a squall line, mayform along or ahead of the front. Squall lines present aserious hazard to pilots as squall type thunderstormsare intense and move quickly. Behind a fast movingcold front, the skies usually clear rapidly and the frontleaves behind gusty, turbulent winds and colder temperatures.

FLIGHT TOWARD AN APPROACHING COLDFRONTLike warm fronts, not all cold fronts are the same.Examining a flight toward an approaching cold front,

pilots can get a better understanding of the type of conditions that can be encountered in flight. Figure 10-27 shows a flight from Pittsburgh, Pennsylvania,toward St. Louis, Missouri.

At the time of departure from Pittsburgh, the weather isVFR with 3 miles visibility in smoke and a scatteredlayer of clouds at 3,500 feet. As the flight progresseswestward to Columbus and closer to the oncoming coldfront, the clouds show signs of vertical developmentwith a broken layer at 2,500 feet. The visibility is 6miles in haze with a falling barometric pressure.Approaching Indianapolis, the weather has deterioratedto overcast clouds at 1,000 feet, and 3 miles visibilitywith thunderstorms and heavy rain showers. At St.Louis, the weather gets better with scattered clouds at1,000 feet and a 10 mile visibility.

A pilot using sound judgment based on the knowledgeof frontal conditions, would most likely remain inIndianapolis until the front had passed. Trying to flybelow a line of thunderstorms or a squall line is hazardous and foolish, and flight over the top of oraround the storm is not an option. Thunderstorms canextend up to well over the capability of small airplanesand can extend in a line for 300 to 500 miles.

COMPARISON OF COLD AND WARM FRONTSWarm fronts and cold fronts are very different in natureas are the hazards associated with each front. They varyin speed, composition, weather phenomenon, and prediction. Cold fronts, which move at 20 to 35 m.p.h.,move very quickly in comparison to warm fronts,which move at only 10 to 25 m.p.h. Cold fronts alsopossess a steeper frontal slope. Violent weather activityis associated with cold fronts and the weather usuallyoccurs along the frontal boundary, not in advance.However, squall lines can form during the summermonths as far as 200 miles in advance of a severe coldfront. Whereas warm fronts bring low ceilings, poorvisibility, and rain, cold fronts bring sudden storms,gusty winds, turbulence, and sometimes hail or tornadoes.

Cold fronts are fast approaching with little or no warning, and they make a complete weather change injust a few hours. The weather clears rapidly after passage and drier air with unlimited visibilities prevail.Warm fronts, on the other hand, provide advance warning of their approach and can take days to passthrough a region.

WIND SHIFTSWind around a high-pressure system rotates in a clockwise fashion, while low-pressure winds rotate in acounter-clockwise manner. When two high-pressuresystems are adjacent, the winds are almost in direct

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opposition to each other at the point of contact. Frontsare the boundaries between two areas of pressure, andtherefore, wind shifts are continually occurring withina front. Shifting wind direction is most pronounced inconjunction with cold fronts.

STATIONARY FRONTWhen the forces of two air masses are relatively equal,the boundary or front that separates them remains stationary and influences the local weather for days.This front is called a stationary front. The weatherassociated with a stationary front is typically a mixturethat can be found in both warm and cold fronts.

OCCLUDED FRONTAn occluded front occurs when a fast-moving coldfront catches up with a slow-moving warm front. Asthe occluded front approaches, warm front weather prevails, but is immediately followed by cold frontweather. There are two types of occluded fronts thatcan occur, and the temperatures of the colliding frontalsystems play a large part in defining the type of frontand the resulting weather. A cold front occlusion occurswhen a fast-moving cold front is colder than the airahead of the slow-moving warm front. When thisoccurs, the cold air replaces the cool air and forces thewarm front aloft into the atmosphere. Typically, thecold front occlusion creates a mixture of weather foundin both warm and cold fronts, providing the air is

relatively stable. A warm front occlusion occurs whenthe air ahead of the warm front is colder than the air ofthe cold front. When this is the case, the cold front ridesup and over the warm front. If the air forced aloft bythe warm front occlusion is unstable, the weather willbe more severe than the weather found in a cold frontocclusion. Embedded thunderstorms, rain, and fog arelikely to occur.

Figure 10-28 depicts a cross-section of a typical coldfront occlusion. The warm front slopes over the prevailing cooler air and produces the warm front typeweather. Prior to the passage of the typical occludedfront, cirriform and stratiform clouds prevail, light toheavy precipitation is falling, visibility is poor, dewpoint is steady, and barometric pressure is falling. During the passage of the front, nimbostratusand cumulonimbus clouds predominate, and toweringcumulus may also be possible. Light to heavy precipitation is falling, visibility is poor, winds are variable, and the barometric pressure is leveling off.After the passage of the front, nimbostratus and altostratus clouds are visible, precipitation is decreasing and clearing, and visibility is improving.

Stationary Front—A boundary between two air masses that are relatively balanced.

Occluded Front—A frontal occlusion occurs when a fast-moving coldfront catches up with a slow-moving warm front. The difference in temperature within each frontal system is a major factor in determiningwhether a cold or warm front occlusion occurs.

1011

1008100510051008

1011

1011 1011 1014

1014

COLD AIR

METAR KSTL 1950Z 30018KT 10SM SCT010 08/02 A2979

METAR KIND 1950Z 20024KT 3SM +TSRA OVC 010 24/23 A2974

METAR KCMH 1950Z 20012KT 6SM HZ BKN025 25/24 A2983

METAR KPIT 1950Z 20012KT 3SM FU SCT035 24/22 A2989

ST. LOUIS INDIANAPOLIS COLUMBUS PITTSBURGH200 MILES 400 MILES 600 MILES

WARM AIR

CUMULONIMBUS

St. Louis Indianapolis Columbus Pittsburgh

4642

10

0661033

74 0713

71 776

7375

370

35

48

12

102122

10

25

Figure 10-27. Cold front cross-section with surface weather chart depiction and associated METAR.

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St. Louis IndianapolisColumbus Pittsburgh

1023

1020101710141011100610051002999999100210051006

1011

1011 1011 1014 1017 1020 1023

COLD AIR

WARM AIR

COLD AIR

CUMULONIMBUS

NIMBOSTRATUS

ALTOSTRATUS

CIRROSTRATUS

CIRRUS

METAR KSTL 1950Z 31023G40KT 8SM SCT035 05/M03 A2976

METAR KCMH 1950Z 16017KT 2SM BR 0VC080 11/10 A2970

METAR KPIT 1950Z 13012KT 75M BKN130 08/04 A3012

METAR KIND 1950Z 29028G45KT 1/2 SM TSRAGR VV005 18/16 A2970

ST. LOUIS INDIANAPOLIS COLUMBUS PITTSBURGH200 MILES 400 MILES 600 MILES

428 32

076

26

522

51

477

402

058 1428 342002066

6212

Figure 10-28. Occluded front cross-section with a weather chart depiction and associated METAR.

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In aviation, weather service is a combined effort of theNational Weather Service (NWS), the Federal AviationAdministration (FAA), the Department of Defense(DOD), and other aviation groups and individuals.Because of the increasing need for worldwide weatherservices, foreign weather organizations also providevital input.

While weather forecasts are not 100 percent accurate,meteorologists, through careful scientific study andcomputer modeling, have the ability to predict theweather patterns, trends, and characteristics withincreasing accuracy. Through a complex system ofweather services, government agencies, andindependent weather observers, pilots and other aviation professionals receive the benefit of this vastknowledge base in the form of up-to-date weatherreports and forecasts. These reports and forecastsenable pilots to make informed decisions regardingweather and flight safety.

OBSERVATIONSThe data gathered from surface and upper altitudeobservations form the basis of all weather forecasts,advisories, and briefings. There are three types ofweather observations: surface, upper air, and radar.

SURFACE AVIATION WEATHER OBSERVATIONSSurface aviation weather observations (METARs) are acompilation of weather elements of the current weatherat ground stations across the United States. The network is made up of government run facilities and privately contracted facilities that provide up-to-date

weather information. Automated weather sources suchas automated weather observing systems (AWOS)and automated surface observing systems (ASOS),as well as other automated facilities, also play a majorrole in the gathering of surface observations.

Surface observations provide local weather conditionsand other relevant information. This informationincludes the type of report, station identifier, date andtime, modifier (as required), wind, visibility, runwayvisual range (RVR), weather phenomena, sky condition, temperature/dewpoint, altimeter reading,and applicable remarks. The information gathered forthe surface observation may be from a person, an automated station, or an automated station that isupdated or enhanced by a weather observer. In anyform, the surface observation provides valuable information about airports around the country.

UPPER AIR OBSERVATIONSObservations of upper air weather prove to be morechallenging than surface observations. There are onlytwo methods by which upper air weather phenomenacan be observed: radiosonde observations and pilot

Automated Weather Observing System (AWOS)—Automated weatherreporting system consisting of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcastweather data.

Automated Surface Observation System (ASOS)—Weather reportingsystem which provides surface observations every minute via digitizedvoice broadcasts and printed reports.

Radiosonde—A weather instrument that observes and reports meteorological conditions from the upper atmosphere. This instrumentis typically carried into the atmosphere by some form of weather balloon.

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weather reports (PIREPs). Using radio telemetry,radiosonde observations are made by sounding balloons from which weather data is received twicedaily. These upper air observations provide temperature, humidity, pressure, and wind data forheights up to and above 100,000 feet. In addition tothis, pilots provide vital information regarding upperair weather observations. Pilots remain the only real-time source of information regarding turbulence,icing, and cloud heights, which is gathered from pilotsin flight, through the filing of pilot weather reports orPIREPs. Together, pilot reports and radiosonde observations provide information on upper air conditions important for flight planning. Many U.S.and international airlines have equipped their aircraftwith instrumentation that automatically transmits in-flight weather observations through the DataLinksystem to the airline dispatcher who disseminates thedata to appropriate weather forecasting authorities.

RADAR OBSERVATIONSWeather observers use three types of radar to provideinformation about precipitation, wind, and weather systems. The WSR-88D NEXRAD radar, commonlycalled Doppler radar, provides in-depth observationsthat inform surrounding communities of impendingweather. FAA terminal doppler weather radar (TDWR),installed at some major airports around the country,also aids in providing severe weather alerts and warnings to airport traffic controllers. Terminal radarensures pilots are aware of wind shear, gust fronts, andheavy precipitation, all of which are dangerous to arriving and departing aircraft. The third type of radarcommonly used in the detection of precipitation is theFAA airport surveillance radar. This radar is used primarily to detect aircraft; however, it also detects thelocation and intensity of precipitation which is used toroute aircraft traffic around severe weather in an airportenvironment.

SERVICE OUTLETSService outlets are government or private facilities thatprovide aviation weather services. Several differentgovernment agencies, including the Federal AviationAdministration (FAA), National Oceanic andAtmospheric Administration (NOAA), and theNational Weather Service (NWS) work in conjunctionwith private aviation companies to provide differentmeans of accessing weather information.

FAA FLIGHT SERVICE STATIONThe FAA Flight Service Station (FSS) is the primarysource for preflight weather information. A preflightweather briefing from an automated FSS (AFSS) canbe obtained 24 hours a day by calling 1-800-WXBRIEF almost anywhere in the U.S. In areas not servedby an AFSS, National Weather Service facilities may

provide pilot weather briefings. Telephone numbers forNWS facilities and additional numbers forFSSs/AFSSs can be found in the Airport/FacilityDirectory (A/FD) or in the U.S. Government section ofthe telephone book.

Flight Service Stations also provide in-flight weatherbriefing services, as well as scheduled and unscheduledweather broadcasts. An FSS may also furnish weatheradvisories to flights within the FSS region of authority.

TRANSCRIBED INFORMATION BRIEFING SERVICE (TIBS)The Transcribed Information Briefing Service (TIBS)is a service which is prepared and disseminated byselected Automated Flight Service Stations. It providescontinuous telephone recordings of meteorological andaeronautical information. Specifically, TIBS providesarea and route briefings, airspace procedures, and special announcements. It is designed to be a preliminary briefing tool and is not intended to replacea standard briefing from an FSS specialist.

The TIBS service is available 24 hours a day and isupdated when conditions change, but it can only beaccessed by a TOUCH-TONE phone. The phonenumbers for the TIBS service are listed in the A/FD.

DIRECT USER ACCESS TERMINAL SERVICE (DUATS)The Direct User Access Terminal Service, which isfunded by the FAA, allows any pilot with a currentmedical certificate to access weather information andfile a flight plan via computer. Two methods of accessare available to connect with DUATS. The first is onthe Internet through DynCorp at http://www.duats.comor Data Transformation Corporation athttp://www.duat.com. The second method requires amodem and a communications program supplied by aDUATS provider. To access the weather informationand file a flight plan by this method, pilots use a tollfree telephone number to connect the user’s computerdirectly to the DUATS computer. The current vendorsof DUATS service and the associated phone numbersare listed in Chapter 7 of the Aeronautical InformationManual (AIM).

ENROUTE FLIGHT ADVISORY SERVICEA service specifically designed to provide timelyenroute weather information upon pilot request isknown as the enroute flight advisory service (EFAS),or Flight Watch. EFAS provides a pilot with weatheradvisories tailored to the type of flight, route, and cruis-ing altitude. EFAS can be one of the best sources forcurrent weather information along the route of flight.

A pilot can usually contact an EFAS specialist from 6a.m. to 10 p.m. anywhere in the conterminous U.S. and

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Puerto Rico. The common EFAS frequency, 122.0MHz, is established for pilots of aircraft flying between5,000 feet AGL and 17,500 feet MSL.

HAZARDOUS IN-FLIGHT WEATHER ADVISORY (HIWAS)HIWAS is a national program for broadcasting haz-ardous weather information continuously over selectednavaids. The broadcasts include advisories such asAIRMETS, SIGMETS, convective SIGMETS, andurgent PIREPs. These broadcasts are only a summaryof the information, and pilots should contact an FSS orEFAS for detailed information. Navaids that haveHIWAS capability are depicted on sectional charts withan “H” in the upper right corner of the identificationbox. [Figure 11-1]

TRANSCRIBED WEATHER BROADCAST(TWEB)A transcribed weather broadcast is a weather reporttransmitted continuously over selected navaids. On asectional chart, a “T” in the upper right-hand corner ofthe navaid box indicates TWEB availability. TWEBweather usually consists of route-orientated data

including route forecasts, forecast outlook, winds aloft,and other selected weather reports for an area within 50nautical miles (NM) of the FSS or for a 50-mile widecorridor along a specific route. A TWEB forecast isvalid for 12 hours and is updated four times a day.

WEATHER BRIEFINGSPrior to every flight, pilots should gather all information vital to the nature of the flight. Thisincludes an appropriate weather briefing obtained froma specialist at an FSS, AFSS, or NWS.

For weather specialists to provide an appropriateweather briefing, they need to know which of the threetypes of briefings is needed—a standard briefing, anabbreviated briefing, or an outlook briefing. Otherhelpful information is whether the flight is visual flightrule (VFR) or instrument flight rule (IFR), aircraftidentification and type, departure point, estimated timeof departure (ETD), flight altitude, route of flight, destination, and estimated time en route (ETE).

This information is recorded in the flight plan system,and a note is made regarding the type of weather briefing provided. If necessary, it can be referencedlater to file or amend a flight plan. It is also used whenan aircraft is overdue or is reported missing.

STANDARD BRIEFINGA standard briefing is the most complete report and provides the overall weather picture. This type of briefing should be obtained prior to the departure ofany flight and should be used during flight planning. Astandard briefing provides the following information insequential order if it is applicable to the route of flight.

1. Adverse Conditions—This includes informa-tion about adverse conditions that may influence a decision to cancel or alter the routeof flight. Adverse conditions includes significant weather, such as thunderstorms oraircraft icing, or other important items such asairport closings.

2. VFR Flight NOT RECOMMENDED—Ifthe weather for the route of flight is belowVFR minimums, or if it is doubtful the flightcould be made under VFR conditions due tothe forecast weather, the briefer may state thatVFR is not recommended. It is the pilot’s decision whether or not to continue the flightunder VFR, but this advisory should beweighed carefully.

3. Synopsis—The synopsis is an overview of thelarger weather picture. Fronts and majorweather systems that affect the general areaare provided.

HSymbol Indicates HIWAS

Figure 11-1. HIWAS availability is shown on sectional chart.

AIRMET—In-flight weather advisory concerning moderate icing,moderate turbulence, sustained winds of 30 knots or more at the surface, and widespread areas of ceilings less than 1,000 feet and/or visibility less than 3 miles.

SIGMET—An in-flight weather advisory that is considered significantto all aircraft. SIGMET criteria include severe icing, severe andextreme turbulence, duststorms, sandstorms, volcanic eruptions, andvolcanic ash that lower visibility to less than 3 miles.

Convective SIGMET—A weather advisory concerning convectiveweather significant to the safety of all aircraft. Convective SIGMETsare issued for tornadoes, lines of thunderstorms, thunderstorms over awide area, embedded thunderstorms, wind gusts to 50 knots or greater,and/or hail 3/4 inch in diameter or greater.

Urgent PIREP—Any pilot report that contains any of the followingweather phenomena: tornadoes, funnel clouds, or waterspouts; severeor extreme turbulence, including clear air turbulence; severe icing; hail;volcanic ash; or low-level wind shear.

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4. Current Conditions—This portion of the briefing contains the current ceilings, visibility, winds, and temperatures. If thedeparture time is more than 2 hours away, current conditions will not be included in thebriefing.

5. En Route Forecast—The en route forecast isa summary of the weather forecast for the proposed route of flight.

6. Destination Forecast—The destination forecast is a summary of the expected weatherfor the destination airport at the estimated timeof arrival (ETA).

7. Winds and Temperatures Aloft—Winds andtemperatures aloft is a report of the winds atspecific altitudes for the route of flight.However, the temperature information is provided only on request.

8. Notices to Airmen—This portion suppliesNOTAM information pertinent to the route offlight which has not been published in theNotice to Airmen publication. PublishedNOTAM information is provided during thebriefing only when requested.

9. ATC Delays—This is an advisory of anyknown air traffic control (ATC) delays thatmay affect the flight.

10. Other Information—At the end of the standard briefing, the FSS specialist will provide the radio frequencies needed to open aflight plan and to contact en route flight advisory service (EFAS). Any additional information requested is also provided at thistime.

ABBREVIATED BRIEFINGAn abbreviated briefing is a shortened version of thestandard briefing. It should be requested when a departure has been delayed or when specific weatherinformation is needed to update the previous briefing.When this is the case, the weather specialist needs toknow the time and source of the previous briefing sothe necessary weather information will not be omittedinadvertently.

OUTLOOK BRIEFINGAn outlook briefing should be requested when aplanned departure is 6 or more hours away. It providesinitial forecast information that is limited in scope dueto the timeframe of the planned flight. This type ofbriefing is a good source of flight planning informationthat can influence decisions regarding route of flight,altitude, and ultimately the go, no-go decision. A

follow-up briefing prior to departure is advisable sincean outlook briefing generally only contains information based on weather trends and existingweather in geographical areas at or near the departureairport.

AVIATION WEATHER REPORTSAviation weather reports are designed to give accuratedepictions of current weather conditions. Each reportprovides current information that is updated at different times. Some typical reports are aviation routine weather reports (METAR), pilot weatherreports (PIREPs), and radar weather reports (SDs).

AVIATION ROUTINE WEATHER REPORT(METAR)An aviation routine weather report, or METAR, is anobservation of current surface weather reported in astandard international format. While the METAR codehas been adopted worldwide, each country is allowedto make modifications to the code. Normally, these differences are minor but necessary to accommodatelocal procedures or particular units of measure. Thisdiscussion of METAR will cover elements used in theUnited States.

Example:

METAR KGGG 161753Z AUTO 14021G26 3/4SM+TSRA BR BKN008 OVC012CB 18/17 A2970 RMKPRESFR

A typical METAR report contains the following information in sequential order:

1. Type of Report—There are two types ofMETAR reports. The first is the routineMETAR report that is transmitted every hour.The second is the aviation selected specialweather report (SPECI). This is a specialreport that can be given at any time to updatethe METAR for rapidly changing weather conditions, aircraft mishaps, or other criticalinformation.

2. Station Identifier—Each station is identifiedby a four-letter code as established by theInternational Civil Aviation Organization(ICAO). In the 48 contiguous states, a uniquethree-letter identifier is preceded by the letter“K.” For example, Gregg County Airport inLongview, Texas, is identified by the letters“KGGG,” K being the country designationand GGG being the airport identifier. In otherregions of the world, including Alaska andHawaii, the first two letters of the four-letterICAO identifier indicate the region, country,

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or state. Alaska identifiers always begin withthe letters “PA” and Hawaii identifiers alwaysbegin with the letters “PH.” A list of stationidentifiers can be found at an FSS or NWSoffice.

3. Date and Time of Report—The date and time(161753Z) are depicted in a six-digit group.The first two digits of the six-digit group arethe date. The last four digits are the time of theMETAR, which is always given inCoordinated Universal Time (UTC). A “Z” isappended to the end of the time to denote thetime is given in Zulu time (UTC) as opposedto local time.

4. Modifier—Modifiers denote that the METARcame from an automated source or that thereport was corrected. If the notation “AUTO”is listed in the METAR, the report came froman automated source. It also lists “AO1” or“AO2” in the remarks section to indicate thetype of precipitation sensors employed at theautomated station.

When the modifier “COR” is used, it identifies a corrected report sent out to replacean earlier report that contained an error.

Example:

METAR KGGG 161753Z COR

5. Wind—Winds are reported with five digits(14021) unless the speed is greater than 99knots, in which case the wind is reported withsix digits. The first three digits indicate thedirection the wind is blowing in tens ofdegrees. If the wind is variable, it is reportedas “VRB.” The last two digits indicate thespeed of the wind in knots (KT) unless thewind is greater than 99 knots, in which case itis indicated by three digits. If the winds aregusting, the letter “G” follows the windspeed(G26). After the letter “G,” the peak gustrecorded is provided. If the wind varies morethan 60° and the windspeed is greater than 6knots, a separate group of numbers, separatedby a “V,” will indicate the extremes of thewind directions.

6. Visibility—The prevailing visibility (3/4 SM)is reported in statute miles as denoted by the letters “SM.” It is reported in both miles andfractions of miles. At times, RVR, or runwayvisual range is reported following the

prevailing visibility. RVR is the distance apilot can see down the runway in a moving aircraft. When RVR is reported, it is shownwith an R, then the runway number followedby a slant, then the visual range in feet. Forexample, when the RVR is reported asR17L/1400FT, it translates to a visual range of1,400 feet on runway 17 left.

7. Weather—Weather can be broken down intotwo different categories: qualifiers andweather phenomenon (+TSRA BR). First, thequalifiers of intensity, proximity, and thedescriptor of the weather will be given. Theintensity may be light (-), moderate ( ), orheavy (+). Proximity only depicts weatherphenomena that are in the airport vicinity. Thenotation “VC” indicates a specific weatherphenomenon is in the vicinity of 5 to 10 milesfrom the airport. Descriptors are used todescribe certain types of precipitation andobscurations. Weather phenomena may bereported as being precipitation, obscurations,and other phenomena such as squalls or funnelclouds. Descriptions of weather phenomena asthey begin or end, and hailstone size are alsolisted in the remarks sections of the report.[Figure 11-2]

8. Sky Condition—Sky condition (BKN008OVC012CB) is always reported in thesequence of amount, height, and type or indefinite ceiling/height (vertical visibility).The heights of the cloud bases are reportedwith a three-digit number in hundreds of feetabove the ground. Clouds above 12,000 feetare not detected or reported by an automatedstation. The types of clouds, specifically towering cumulus (TCU) or cumulonimbus(CB) clouds, are reported with their height.Contractions are used to describe the amountof cloud coverage and obscuring phenomena.The amount of sky coverage is reported ineighths of the sky from horizon to horizon.[Figure 11-3]

9. Temperature and Dewpoint—The air temperature and dewpoint are always given indegrees Celsius (18/17). Temperatures below0°C are preceded by the letter “M” to indicateminus.

10. Altimeter Setting—The altimeter setting isreported as inches of mercury in a four-digitnumber group (A2970). It is always precededby the letter “A.” Rising or falling pressuremay also be denoted in the remarks sections as“PRESRR” or “PRESFR” respectively.

Zulu Time—A term used in aviation for coordinated universal time(UTC) which places the entire world on one time standard.

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11-6

11. Remarks—Comments may or may not appearin this section of the METAR. The informationcontained in this section may include winddata, variable visibility, beginning and endingtimes of particular phenomenon, pressureinformation, and various other informationdeemed necessary. An example of a remarkregarding weather phenomenon that does notfit in any other category would be: OCNLLTGICCG. This translates as occasional lightning in the clouds, and from cloud toground. Automated stations also use theremarks section to indicate the equipmentneeds maintenance. The remarks sectionalways begins with the letters “RMK.”

Example:

METAR BTR 161753Z 14021G26 3/4SM -RA BR BKN008 OVC012 18/17 A2970 RMK PRESFR

Explanation:Type of Report: ...............Routine METARLocation: ........................Baton Rouge, LouisianaDate: ...............................16th day of the monthTime: ..............................1753 ZuluModifier: ........................None shownWind Information: ..........Winds 140° at 21 knots

gusting to 26 knotsVisibility: ........................3/4 statute mileWeather: .........................light rain and mistSky Conditions: ..............Skies broken 800 feet,

overcast 1,200Temperature: ..................Temperature 18°C, dewpoint

17°CAltimeter: .......................29.70 in. Hg.Remarks: ........................Barometric pressure is

falling.

Qualifier Weather PhenomenaIntensity

orProximity

1

Descriptor

2

Precipitation

3

Obscuration

4

Other

5

- Light

Moderate (no qualifier)

+ Heavy

VC in the vicinity

MI Shallow

BC Patches

DR Low Drifting

BL Blowing

SH Showers

TS Thunderstorms

FZ Freezing

PR Partial

DZ Drizzle

RA Rain

SN Snow

SG Snow grains

IC Ice Crystals (diamond dust)

PL Ice Pellets

GR Hail

GS Small hail or snow pellets

UP *Unknown Precipitation

BR Mist

FG Fog

FU Smoke

DU Dust

SA Sand

HZ Haze

PY Spray

VA Volcanic ash

PO Dust/sand whirls

SQ Squalls

FC Funnel cloud

+FC Tornado or Waterspout

SS Sandstorm

DS Dust storm

The weather groups are constructed by considering columns 1-5 in this table, in sequence;i.e., intensity, followed by descriptor, followed by weather phenomena; i.e., heavy rain showers(s)is coded as +SHRA. * Automated stations only

Figure 11-2. Descriptors and weather phenomena used in a typical METAR.

Figure 11-3. Reportable contractions for sky condition.

Sky Cover Less than 1/8(Clear)

1/8 - 2/8(Few)

3/8 - 4/8(Scattered)

5/8 - 7/8(Broken)

8/8 or Overcast(Overcast)

ContractionSKCCLRFEW

FEW SCT BKN OVC

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11-7

PILOT WEATHER REPORTS (PIREPs)Pilot weather reports provide valuable informationregarding the conditions as they actually exist in theair, which cannot be gathered from any other source.Pilots can confirm the height of bases and tops ofclouds, locations of wind shear and turbulence, and thelocation of in-flight icing. If the ceiling is below 5,000feet, or visibility is at or below 5 miles, ATC facilitiesare required to solicit PIREPs from pilots in the area.When unexpected weather conditions are encountered,pilots are encouraged to make a report to an FSS orATC. When a pilot weather report is filed, the ATCfacility or FSS will add it to the distribution system tobrief other pilots and provide in-flight advisories.

PIREPs are easy to file and a standard reporting formoutlines the manner in which they should be filed.Figure 11-4 shows the elements of a PIREP form. Itemnumbers one through five are required informationwhen making a report, as well as at least one weatherphenomenon encountered. PIREPs are normally transmitted as an individual report, but may be

appended to a surface report. Pilot reports are easilydecoded and most contractions used in the reports areself-explanatory.

Example:

UA/OV GGG 090025/ M 1450/ FL 060/ TP C182/ SK080 OVC/ WX FV 04R/ TA 05/ WV 270030/ TB LGT/ RM HVY RAIN

Explanation: Type: ...............................Routine pilot reportLocation: ........................25 NM out on the 090°

radial, Gregg County VORTime: ..............................1450 ZuluAltitude or Flight Level: 6,000 feetAircraft Type: .................Cessna 182Sky Cover: ......................8,000 overcastVisibility/Weather: ..........4 miles in rainTemperature: ..................5° CelsiusWind: ..............................270° at 30 knotsTurbulence: ....................LightIcing: ..............................None reportedRemarks: ........................Rain is heavy.

Figure 11-4. PIREP encoding and decoding.

Pilot Weather Report—A report, generated by pilots, concerning meteorological phenomenon encountered in flight.

Ch 11.qxd 10/24/03 8:17 AM Page 11-7

RADAR WEATHER REPORTS (SD)Areas of precipitation and thunderstorms are observedby radar on a routine basis. Radar weather reports areissued by radar stations at 35 minutes past the hour,with special reports issued as needed.

Radar weather reports provide information on the type,intensity, and location of the echo top of the precipitation. [Figure 11-5] These reports may alsoinclude direction and speed of the area of precipitationas well as the height and base of the precipitation inhundreds of feet MSL. RAREPs are especially valuable for preflight planning to help avoid areas ofsevere weather. However, radar only detects objects inthe atmosphere that are large enough to be consideredprecipitation. Cloud bases and tops, ceilings, and visibility are not detected by radar.

A typical RAREP will include:

• Location identifier and time of radar observation.

• Echo pattern:

1. Line (LN)—A line of precipitationechoes at least 30 miles long, at least fourtimes as long as it is wide, and at least 25 per-cent coverage within the line.

2. Area (AREA)—A group of echoes ofsimilar type and not classified as a line.

3. Single Cell (CELL)—A single isolated convective echo such as a rain shower.

• Area coverage in tenths.

• Type and intensity of weather.

• Azimuth, referenced to true north, and range, innautical miles, from the radar site, of points defining the echo pattern. For lines and areas,there will be two azimuth and range sets thatdefine the pattern. For cells, there will be only oneazimuth and range set.

• Dimension of echo pattern—The dimension of anecho pattern is given when the azimuth and rangedefine only the center line of the pattern.

• Cell movement—Movement is only coded forcells; it will not be coded for lines or areas.

• Maximum top of precipitation and location.Maximum tops may be coded with the symbols“MT” or “MTS.” If it is coded with “MTS,” itmeans that satellite data as well as radar information was used to measure the top of theprecipitation.

• If the word “AUTO” appears in the report, itmeans the report is automated from WSR-88Dweather radar data.

• The last section is primarily used to prepare radarsummary charts, but can be used during preflightto determine the maximum precipitation intensitywithin a specific grid box. The higher the number,the greater the intensity. Two or more numbersappearing after a grid box reference, such asPM34, indicates precipitation in consecutive gridboxes.

Example:

TLX 1935 LN 8 TRW++ 86/40 199/115 20W C2425 MTS 570 AT 159/65 AUTO^MO1 NO2 ON3 PM34 QM3 RL2=

11-8

Radar is operating normally but there are no echoes being detected.

SYMBOL MEANING

R Rain

RW Rain Shower

S Snow

SW Snow Shower

T Thunderstorm

SYMBOL INTENSITY

- Light

(none) Moderate

+ Heavy

++ Very Heavy

X Intense

XX Extreme

CONTRACTION OPERATIONAL STATUS

PPINE

PPINA

PPIOM

AUTO

Radar observation is not available.

Radar is inoperative or out of service.

Automated radar report from WSR-88D.

Figure 11-5. Radar weather report codes.

Ch 11.qxd 10/24/03 8:17 AM Page 11-8

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Explanation:

The radar report gives the following information: Thereport is automated from Oklahoma City and was madeat 1935 UTC. The echo pattern for this radar reportindicates a line of echos covering 8/10ths of the area.Thunderstorms and very heavy rain showers are indicated. The next set of numbers indicate the azimuththat defines the echo (86° at 40 NM and 199° at 115NM). Next, the dimension of this echo is given as 20nautical miles wide (10 nautical miles on either side ofthe line defined by the azimuth and range). The cellswithin the line are moving from 240° at 25 knots. Themaximum top of the precipitation, as determined byradar and satellite, is 57,000 feet and it is located on the159° radial, 65 NM out. The last line indicates theintensity of the precipitation, for example in grid QMthe intensity is 3 or heavy precipitation. (1 is light and6 is extreme.)

AVIATION FORECASTSObserved weather condition reports are often used inthe creation of forecasts for the same area. A variety ofdifferent forecast products are produced and designedto be used in the preflight planning stage. The printedforecasts that pilots need to be familiar with are the terminal aerodrome forecast (TAF), aviation area forecast (FA), in-flight weather advisories (SIGMET,AIRMET), and the winds and temperatures aloft forecast (FD).

TERMINAL AERODROME FORECASTS (TAF)A terminal aerodrome forecast is a report establishedfor the 5 statute mile radius around an airport. TAFreports are usually given for larger airports. Each TAFis valid for a 24-hour time period, and is updated fourtimes a day at 0000Z, 0600Z, 1200Z, and 1800Z. TheTAF utilizes the same descriptors and abbreviations asused in the METAR report.

The terminal forecast includes the following information in sequential order:

1. Type of Report—A TAF can be either a routine forecast (TAF) or an amended forecast(TAF AMD).

2. ICAO Station Identifier—The station identifier is the same as that used in a METAR.

3. Date and Time of Origin—Time and date ofTAF origination is given in the six-numbercode with the first two being the date, the lastfour being the time. Time is always given inUTC as denoted by the Z following the number group.

4. Valid Period Date and Time—The validforecast time period is given by a six-digitnumber group. The first two numbers indicatethe date, followed by the two-digit beginningtime for the valid period, and the last two digits are the ending time.

5. Forecast Wind—The wind direction andspeed forecast are given in a five-digit numbergroup. The first three indicate the direction ofthe wind in reference to true north. The lasttwo digits state the windspeed in knots asdenoted by the letters “KT.” Like the METAR,winds greater than 99 knots are given in threedigits.

6. Forecast Visibility—The forecast visibility isgiven in statute miles and may be in wholenumbers or fractions. If the forecast is greaterthan 6 miles, it will be coded as “P6SM.”

7. Forecast Significant Weather—Weatherphenomenon is coded in the TAF reports in thesame format as the METAR. If no significantweather is expected during the forecast timeperiod, the denotation “NSW” will be includedin the “becoming” or “temporary” weathergroups.

8. Forecast Sky Condition—Forecast sky con-ditions are given in the same manner as theMETAR. Only cumulonimbus (CB) clouds areforecast in this portion of the TAF report asopposed to CBs and towering cumulus in theMETAR.

9. Forecast Change Group—For any significant weather change forecast to occurduring the TAF time period, the expected conditions and time period are included in thisgroup. This information may be shown asFrom (FM), Becoming (BECMG), andTemporary (TEMPO). “From” is used when arapid and significant change, usually within anhour, is expected. “Becoming” is used when agradual change in the weather is expected overa period of no more than 2 hours. “Temporary”is used for temporary fluctuations of weather,expected to last for less than an hour.

10. Probability Forecast—The probability forecast is given percentage that describes theprobability of thunderstorms and precipitationoccurring in the coming hours. This forecast isnot used for the first 6 hours of the 24-hourforecast.

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Example:

TAFKPIR 111130Z 111212 15012KT P6SM BKN090TEMPO 1214 5SM BRFM1500 16015G25KT P6SM SCT040 BKN250FM0000 14012KT P6SM BKN080 OVC150 PROB400004 3SM TSRA BKN030CBFM0400 1408KT P6SM SCT040 OVC080 TEMPO0408 3SM TSRA OVC030CBBECMG 0810 32007KT=

Explanation:

Routine TAF for Pierre, South Dakota…on the 11th dayof the month, at 1130Z…valid for 24 hours from 1200Zon the 11th to 1200Z on the 12th …wind from 150° at 12knots…visibility greater than 6 statute miles…brokenclouds at 9,000 feet…temporarily, between 1200Z and1400Z, visibility 5 statute miles in mist…from 1500Zwinds from 160° at 15 knots, gusting to 25 knotsvisibility greater than 6 statute miles…clouds scatteredat 4,000 feet and broken at 25,000 feet…from 0000Zwind from 140° at 12 knots…visibility greater than 6statute miles…clouds broken at 8,000 feet, overcast at15,000 feet…between 0000Z and 0400Z, there is 40percent probability of visibility 3 statute miles…thunderstorm with moderate rain showers…clouds broken at 3,000 feet with cumulonimbus clouds…from0400Z…winds from 140° at 8 knots…visibility greaterthan 6 miles…clouds at 4,000 scattered and overcast at8,000…temporarily between 0400Z and 0800Z…visibility 3 miles…thunderstorms with moderate rainshowers…clouds overcast at 3,000 feet with cumulonimbus clouds…becoming between 0800Z and1000Z…wind from 320° at 7 knots…end of report (=).

AREA FORECASTS (FA)The aviation area forecast (FA) gives a picture ofclouds, general weather conditions, and visual meteorological conditions (VMC) expected over alarge area encompassing several states. There are sixareas for which area forecasts are published in the contiguous 48 states. Area forecasts are issued threetimes a day and are valid for 18 hours. This type offorecast gives information vital to en route operationsas well as forecast information for smaller airports thatdo not have terminal forecasts.

Area forecasts are typically disseminated in four sections and include the following information:

1. Header—This gives the location identifier ofthe source of the FA, the date and time ofissuance, the valid forecast time, and the areaof coverage.

Example:

DFWC FA 120945SYNOPSIS AND VFR CLDS/WXSYNOPSIS VALID UNTIL 130400CLDS/WX VALID UNTIL 122200…OTLK VALID122200-130400OK TX AR LA MS AL AND CSTL WTRS

Explanation:

The area forecast shows information given by DallasFort Worth, for the region of Oklahoma, Texas,Arkansas, Louisiana, Mississippi, and Alabama, aswell as a portion of the gulf coastal waters. It wasissued on the 12th day of the month at 0945. The synopsis is valid from the time of issuance until 0400hours on the 13th. VFR clouds and weather informationon this area forecast is valid until 2200 hours on the12th and the outlook is valid until 0400 hours on the13th.

2. Precautionary Statements—IFR conditions,mountain obscurations, and thunderstorm hazards are described in this section.Statements made here regarding height aregiven in MSL, and if given otherwise, AGL orCIG (ceiling) will be noted.

Example:

SEE AIRMET SIERRA FOR IFR CONDS ANDMTN OBSCN.TS IMPLY SEV OR GTR TURB SEV ICE LLWSAND IFR CONDS.NON MSL HGTS DENOTED BY AGL OR CIG.

Explanation:

The area forecast covers VFR clouds and weather, sothe precautionary statement warns that AIRMET Sierrashould be referenced for IFR conditions and mountainobscuration. The code TS indicates the possibility ofthunderstorms and implies there may be an occurrenceof severe or greater turbulence, severe icing, low-levelwind shear, and IFR conditions. The final line of theprecautionary statement alerts the user that heights, forthe most part, are mean sea level (MSL). Those that arenot MSL will be above ground level (AGL) or ceiling(CIG).

3. Synopsis—The synopsis gives a brief summary identifying the location and movement of pressure systems, fronts, and circulation patterns.

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Example:

SYNOPSIS…LOW PRES TROF 10Z OK/TX PNHDLAREA FCST MOV EWD INTO CNTRL-SWRN OKBY 04Z. WRMFNT 10Z CNTRL OK-SRN AR-NRNMS FCST LIFT NWD INTO NERN OK-NRN AREXTRM NRN MS BY 04Z.

Explanation:

As of 1000 Zulu, there is a low pressure trough overthe Oklahoma and Texas panhandle area, which is forecast to move eastward into central southwesternOklahoma by 0400 Zulu. A warm front located overcentral Oklahoma, southern Arkansas, and northernMississippi at 1000 Zulu is forecast to lift northwest-ward into northeastern Oklahoma, northern Arkansas,and extreme northern Mississippi by 0400 Zulu.

4. VFR Clouds and Weather—This sectionlists expected sky conditions, visibility, andweather for the next 12 hours and an outlookfor the following 6 hours.

Example:

S CNTRL AND SERN TXAGL SCT-BKN010. TOPS 030. VIS 3-5SM BR. 14-16Z BECMG AGL SCT030. 19Z AGL SCT050. OTLK…VFR

OKPNDL AND NW…AGL SCT030 SCT-BKN100.TOPS FL200. 15Z AGL SCT040 SCT100. AFT 20Z SCT TSRADVLPG..FEW POSS SEV. CB TOPS FL450.OTLK…VFR

Explanation:

In south central and southeastern Texas, there is a scattered to broken layer of clouds from 1,000 feetAGL with tops at 3,000 feet, visibility is 3 to 5 statutemiles in mist. Between 1400 Zulu and 1600 Zulu, thecloud bases are expected to increase to 3,000 feet AGL.After 1900 Zulu, the cloud bases are expected to continue to increase to 5,000 feet AGL and the outlookis VFR.

In northwestern Oklahoma and panhandle, the cloudsare scattered at 3,000 feet with another scattered to broken layer at 10,000 feet AGL, with the tops at20,000 feet. At 1500 Zulu, the lowest cloud base isexpected to increase to 4,000 feet AGL with a scatteredlayer at 10,000 feet AGL. After 2000 Zulu, the forecastcalls for scattered thunderstorms with rain developingand a few becoming severe; the cumulonimbus cloudswill have tops at flight level 450 or 45,000 feet MSL.

It should be noted that when information is given in thearea forecast, locations may be given by states, regions,or specific geological features such as mountainranges. Figure 11-6 shows an area forecast chart with

SouthDelta Area

NW NENorth

Central Low

er

Mis

siss

ippi V

alle

y

SW SE

NW NE

Ozarks

Boot

Hee

l

SW MissouriLakes Area

Lake of theOzarks Area

ExtremeSRN

IL

SW SE

Central

NW NE

NW NE

SW SECentra

l

Iowa

SW SEExtrm

SE

NW NE

Northeast LakesRegion

UpperMississippi

Valley

Arrowhead

Lake Superior

Shoreline

WRNUpper

MI

CntrlUpper

MI

ERNUpper

MI

Doo

r Pe

nnin

sula

Mackinac Area

NR

N H

ighl

ands

La

keM

ich

Sh

ore

line The

Thumb

Saginaw

Valley

GrandValley

Irish

Hill

s

Near Lake

Mi ExtrmN

NW NE

SW SE

Near Ohio R

iver

SW

SEWest

NCntrl

NorthernSouthern C

ntr

lE

ast

NE

West

MiddleEast

App

alac

hian

Mou

ntai

ns

SE

NENWAlong

Ohi

o

River

ExtrmNW

SWRNSouthern

WCntrl

ECntrl

N Third

SThird

Near Lake Erie

LeeLakeErie

Lower Great

Lakes Basin

ExtrmNW

Alle

gh

en

yP

late

au

NW

SWS

Cntrl

NE

SE

NCntrl

Lee

Lak

e Ont a rio

NRN

SRNNE

Eastern

Shore CoastalWaters

NENW

SW

SE

Co

ast

al

Pla

in

NE

SE

Pie

dmon

t

West

Mtnsof

SC

Coast

alP

lain

NWMtns

Hillsof

Alabama

West

Cntrl

East

Cntrl

ExtrmSE

Extrm SouthernGeorgiaM

obile

Area FL W 85° Extrm

North

North

Central

ApalacheeBay

South

Extrm

South

UpperKeys

Lower Keys

Gul

fS

trea

m

Florida Straits

CoastalWaters

Catskill

Mtns

E Cntrl Cape Cod

Coasta

l Plains

Hu

dso

n V

alle

y

MohawkValley

West of

Catskills

AdirondackMtns

ChamplainValley

Gre

en

Mtn

s

N of Catskills Wh

ite

Mtn

s

NWNE

Coa

stal

SectionSE

SW

MN

IA

MI

IL IN

MO

AR

LA

MSAL

TN

GA

FL

SC

NC

VA

MD

DC

NJ

OH

WI

WV

PA

NY

ME

VTNH MA

RICT

CHIChicago

BOSBoston

MIA Miami

Coastal Waters- From Coast Outward to the Flight Information Region Border

SWSE

Northern

NEMtns

Central

Strait of Juan De Fuca

Olympic Mtns

Sac

ram

ento

Val

ley

NorthWest

North Central

South Central

LowerRio

GrandeValley

LowerCoastal

Plain

Mid

Coast

al

Plain

Upper Coastal

Plain

NorthWest

Texas

Puget

Sound

Casca

de M

tns

Cas

cade

Mtn

s

of C

asca

des

MtnsNE WA

ColumbiaBasin

InteriorValley

Columbia GorgeBlue

Mtns

Wallowa

Mtns

Mtns of

NE OR

Cos

tal R

ange

Will

amet

te V

alle

y

Coast andCostal Valley

High Plateau

Eas

t Slo

pes

WA

OR

Sha

sta

Sis

kiyo

us

NE CA

NRNSierraMtns

Co

ast

al M

tns

an

d V

alle

ys

San

Joa

quin

Val

ley

SRN

Sierra

Mtns

Coa

stal

Mtn

s an

d V

alle

ys

WesternNevadaEasternNevada

CoastalAreas

DeathValley

LakeTahoe

LakeMead

LakeMojave

Mojave

DesertAntelopeValleyCoastal Range

SRNDeserts

SantaBarbaraChannel

Santa MonicaBay

Coastal Plain

Gulf ofSanta Catalina

Coacnellaand

ImperialValleys

GreatBasin

Col

orad

oR

iver

Valle

y

Gilariver Valley

Mogollon Rim

Chiricahua

Mtns

WhiteMtns

LittleColorado

Valley

Grand Canyon

Four

Corners

Area

Lake

Powell

ExtrmSW

Uinta Basin

S CntrlMtns

GreatSaltLake

Was

atch

Mtn

s

West CenrtalValleys

San JuanMtns

NW

CntrlColorado

MtnsSo Platte Valley

NE

Palmer Lake Ridgeor Divide

Eastern PlainsLower Arkansas

Valley

SE

San LuisValley

North Park

Rio

Gra

nde

Val

leyC

ontin

en

tal Divid

e

Sac

rem

ento

Mtn

sSa

ngre

De

Cris

to

Mtn

s

Eas

tern

New

Mex

ico

EasternPlains

Gre

en R

iver

Bas

in

So CentralMtns

SW WY

Laramie M

tns

NPlatte River ValleySE

WY

BlackHills

NE WY

Big HornMtns

Big HornBasin

Wind River M

tns

Teto

nM

tnsSnake River Valley

CentralMtns(Sawtooth)

YellowstonePark

Bitt

ero

ot

Ra

ng

e

Fla

the

ad

Va

lley

EastSlopes ofCont Dvd

SWRNMtns

Fort Peck Reservoir

Wind RiverBasin

E of Cont Dvd

Pec os River

West ofPecos

Big BendArea

East ofPecos

SouthWest

Pan Handle

NorthEast

SouthEast

Coastal Bend

SouthWestSouthEast

Pan Handle NorthEast

High PlainsFlintHills

Marias DesCygne Basin

KansasRiver Valley

Blue RiverValleyLower

RepublicanValley

Chyenne

River

JamesRiver

NE Lakes

Region

RosebudCountry

PineRidge Area

Big Bend

Reservoir

North ofBlackHills

LakeL

ewis and

FrancisC

ase

Clark

Dame Reservoir

MissouriSlope

SourisRiver Valley

Sand Hills

Central Nebraska

Nebraskapan

Handle

Pl atte River Ba sin

SE

NE

SFOSan Francisco

DFWDallas/Fort Worth

SLCSalt Lake City

CA

NV

ID

MTND

SD

NE

KS

OK

TX

WY

UT

CO

AZ

NM

Re

dR

ive

rV

alle

y

Figure 11-6. Area forecast region map.

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six regions of forecast, states, regional areas, and common geographical features.

IN-FLIGHT WEATHER ADVISORIESIn-flight weather advisories, which are provided to enroute aircraft, are forecasts that detail potentially hazardous weather. These advisories are also availableto pilots prior to departure for flight planning purposes.An in-flight weather advisory is issued in the form ofeither an AIRMET, SIGMET, or Convective SIGMET.

AIRMAN’S METEOROLOGICAL INFORMATION(AIRMET)AIRMETs (WAs) are examples of in-flight weatheradvisories that are issued every 6 hours with intermediate updates issued as needed for a particulararea forecast region. The information contained in anAIRMET is of operational interest to all aircraft, butthe weather section concerns phenomena consideredpotentially hazardous to light aircraft and aircraft withlimited operational capabilities.

An AIRMET includes forecast of moderate icing, moderate turbulence, sustained surface winds of 30knots or greater, widespread areas of ceilings less than1,000 feet and/or visibilities less than 3 miles, andextensive mountain obscurement.

Each AIRMET bulletin has a fixed alphanumeric designator, numbered sequentially for easy identification, beginning with the first issuance of theday. SIERRA is the AIRMET code used to denoteinstrument flight rules (IFR) and mountain obscuration; TANGO is used to denote turbulence,strong surface winds, and low-level wind shear; andZULU is used to denote icing and freezing levels.

Example:

DFWT WA 241650AIRMET TANGO UPDT 3 FOR TURBC… STGSFC WINDS AND LLWS VALID UNTIL 242000

AIRMET TURBC… OK TX…UPDTFROM OKC TO DFW TO SAT TO MAF TO CDSTO OKC OCNL MDT TURBC BLO 60 DUE TOSTG AND GUSTY LOW LVL WINDS. CONDSCONTG BYD 2000Z

Explanation:

This AIRMET was issued by Dallas Fort Worth on the24th day of the month, at 1650 Zulu time. On this thirdupdate, the AIRMET Tango is issued for turbulence,strong surface winds, and low-level wind shear until2000 Zulu on the same day. The turbulence section ofthe AIRMET is an update for Oklahoma and Texas. It

defines an area from Oklahoma City to Dallas, Texas,to San Antonio, to Midland, Texas, to Childress, Texas,to Oklahoma City that will experience occasional moderate turbulence below 6,000 feet due to strong andgusty low-level winds. It also notes that these conditions are forecast to continue beyond 2000 Zulu.

SIGNIFICANT METEOROLOGICAL INFORMATION (SIGMET)SIGMETs (WSs) are in-flight advisories concerningnon-convective weather that is potentially hazardous toall aircraft. They report weather forecasts that includesevere icing not associated with thunderstorms, severeor extreme turbulence or clear air turbulence (CAT) notassociated with thunderstorms, dust storms or sandstorms that lower surface or in-flight visibilities tobelow 3 miles, and volcanic ash.

SIGMETs are unscheduled forecasts that are valid for4 hours, but if the SIGMET relates to hurricanes, it isvalid for 6 hours.

A SIGMET is issued under an alphabetic identifier,from November through Yankee, excluding Sierra andTango. The first issuance of a SIGMET is designated asa UWS, or Urgent Weather SIGMET. Re-issuedSIGMETs for the same weather phenomenon aresequentially numbered until the weather phenomenonends.

Example:

SFOR WS 100130SIGMET ROME02 VALID UNTIL 100530OR WAFROM SEA TO PDT TO EUG TO SEAOCNL MOGR CAT BTN 280 AND 350 EXPCDDUE TO JTSTR.CONDS BGNG AFT 0200Z CONTG BYD 0530Z .

Explanation:

This is SIGMET Romeo 2, the second issuance for thisweather phenomenon. It is valid until the 10th day ofthe month at 0530 Zulu time. This SIGMET is forOregon and Washington, for a defined area fromSeattle to Portland to Eugene to Seattle. It calls foroccasional moderate or greater clear air turbulencebetween 28,000 and 35,000 feet due to the location ofthe jetstream. These conditions will be beginning after0200 Zulu and will continue beyond the forecast scopeof this SIGMET of 0530 Zulu.

CONVECTIVE SIGNIFICANT METEOROLOGICALINFORMATION (WST)A Convective SIGMET (WST) is an in-flight weatheradvisory issued for hazardous convective weather thataffects the safety of every flight. Convective SIGMETs

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are issued for severe thunderstorms with surface windsgreater than 50 knots, hail at the surface greater than or equal to 3/4 inch in diameter, or tornadoes. They are also issued to advise pilots of embedded thunderstorms, lines of thunderstorms, or thunderstorms with heavy or greater precipitationthat affect 40 percent or more of a 3,000 square foot orgreater region.

Convective SIGMETs are issued for each area of thecontiguous 48 states but not Alaska or Hawaii.Convective SIGMETs are issued for the eastern (E),western (W), and central (C) United States. Each reportis issued at 55 minutes past the hour, but special reportscan be issued during the interim for any reason. Eachforecast is valid for 2 hours. They are numberedsequentially each day from 1-99, beginning at 00 Zulutime. If no hazardous weather exists, the ConvectiveSIGMET will still be issued; however, it will state“CONVECTIVE SIGMET…. NONE.”

Example:

MKCC WST 221855CONVECTIVE SIGMET 21CVALID UNTIL 2055KS OK TXVCNTY GLD-CDS LINENO SGFNT TSTMS RPRTDLINE TSTMS DVLPG BY 1955Z WILL MOV EWD30-35 KT THRU 2055ZHAIL TO 2 IN PSBL

Explanation:

This Convective SIGMET provides the followinginformation: The WST indicates this report is aConvective SIGMET. The current date is the 22nd ofthe month and it was issued at 1855 Zulu. It isConvective SIGMET number 21C, indicating that it isthe 21st consecutive report issued for the central UnitedStates. This report is valid for 2 hours until 2055 Zulutime. The Convective SIGMET is for an area fromKansas to Oklahoma to Texas, in the vicinity of a linefrom Goodland, Kansas, to Childress, Texas. No significant thunderstorms are being reported, but a lineof thunderstorms will develop by 1955 Zulu time andwill move eastward at a rate of 30-35 knots through2055 Zulu. Hail up to 2 inches in size is possible withthe developing thunderstorms.

WINDS AND TEMPERATURE ALOFT FORECAST (FD)Winds and temperatures aloft forecasts provide windand temperature forecasts for specific locations in thecontiguous United States, including network locationsin Hawaii and Alaska. The forecasts are made twice aday based on the radiosonde upper air observationstaken at 0000Z and 1200Z.

Through 12,000 feet are true altitudes and above18,000 feet are pressure altitudes. Wind direction isalways in reference to true north and windspeed isgiven in knots. The temperature is given in degreesCelsius. No winds are forecast when a given level iswithin 1,500 feet of the station elevation. Similarly,temperatures are not forecast for any station within2,500 feet of the station elevation.

If the windspeed is forecast to be greater than 100 knotsbut less than 199 knots, the computer adds 50 to thedirection and subtracts 100 from the speed. To decodethis type of data group, the reverse must be accomplished. For example, when the data appears as“731960,” subtract 50 from the 73 and add 100 to the19, and the wind would be 230° at 119 knots with atemperature of –60°C. If the windspeed is forecast tobe 200 knots or greater, the wind group is coded as 99knots. For example, when the data appears as “7799,”subtract 50 from 77 and add 100 to 99, and the wind is270° at 199 knots or greater. When the forecast windspeed is calm or less than 5 knots, the data groupis coded “9900,” which means light and variable.[Figure 11-7]

Explanation of figure 11-7:

The heading indicates that this FD was transmitted onthe 15th of the month at 1640Z and is based on the 1200Zulu radiosonde. The valid time is 1800 Zulu on thesame day and should be used for the period between1700Z and 2100Z. The heading also indicates that thetemperatures above 24,000 feet MSL are negative.Since the temperatures above 24,000 feet are negative,the minus sign is omitted.

A 4-digit data group shows the wind direction in reference to true north, and the windspeed in knots. Theelevation at Amarillo, TX (AMA) is 3,605 feet, so thelowest reportable altitude is 6,000 feet for the forecastwinds. In this case, “2714” means the wind is forecastto be from 270° at a speed of 14 knots.

A 6-digit group includes the forecast temperature aloft.The elevation at Denver (DEN) is 5,431 feet, so thelowest reportable altitude is 9,000 feet for the windsand temperature forecast. In this case, “2321-04” indicates the wind is forecast to be from 230° at a speedof 21 knots with a temperature of –4°C.

FD KWBC 151640BASED ON 151200Z DATAVALID 151800Z FOR USE 1700-2100Z TEMPS NEGATIVE ABV 24000FD 3000 6000 9000 12000 18000 24000 30000AMA 2714 2725+00 2625-04 2531-15 2542-27 265842DEN 2321-04 2532-08 2434-19 2441-31 235347

Figure 11-7. Winds and temperatures aloft forecast.

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WEATHER CHARTSWeather charts are graphic charts that depict current orforecast weather. They provide an overall picture of theUnited States and should be used in the beginningstages of flight planning. Typically, weather chartsshow the movement of major weather systems andfronts. Surface analysis, weather depiction, and radarsummary charts are sources of current weather information. Significant weather prognostic charts provide an overall forecast weather picture.

SURFACE ANALYSIS CHARTThe surface analysis chart, depicts an analysis of thecurrent surface weather. [Figure 11-8] This chart is acomputer prepared report that is transmitted every 3hours and covers the contiguous 48 states and adjacentareas. A surface analysis chart shows the areas of highand low pressure, fronts, temperatures, dewpoints,wind directions and speeds, local weather, and visualobstructions.

Surface weather observations for reporting pointsacross the United States are also depicted on this chart.Each of these reporting points is illustrated by a stationmodel. [Figure 11-9] A station model will include:

• Type of Observation—A round model indicatesan official weather observer made the observation. A square model indicates the

observation is from an automated station.Stations located offshore give data from ships,buoys, or offshore platforms.

• Sky Cover—The station model depicts total skycover and will be shown as clear, scattered, broken, overcast, or obscured/partially obscured.

• Clouds—Cloud types are represented by specificsymbols. Low cloud symbols are placed beneaththe station model, while middle and high cloudsymbols are placed directly above the stationmodel. Typically, only one type of cloud will bedepicted with the station model.

• Sea Level Pressure—Sea level pressure given inthree digits to the nearest tenth of a millibar. For1000 mbs or greater, prefix a 10 to the three digits. For less than 1000 mbs, prefix a 9 to thethree digits.

• Pressure Change/Tendency—Pressure changein tenths of millibars over the past 3 hours. Thisis depicted directly below the sea level pressure.

• Precipitation—A record of the precipitation thathas fallen over the last 6 hours to the nearest hundredth of an inch.

• Dewpoint—Dewpoint is given in degreesFahrenheit.

Figure 11-8. Surface analysis chart.

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• Present Weather—Over 100 different weathersymbols are used to describe the current weather.

• Temperature—Temperature is given in degreesFahrenheit.

• Wind—True direction of wind is given by thewind pointer line, indicating the direction fromwhich the wind is coming. A short barb is equalto 5 knots of wind, a long barb is equal to 10knots of wind, and a pennant is equal to 50 knots.

WEATHER DEPICTION CHARTA weather depiction chart details surface conditions asderived from METAR and other surface observations.

The weather depiction chart is prepared and transmitted by computer every 3 hours beginning at0100 Zulu time, and is valid at the time of the plotteddata. It is designed to be used for flight planning bygiving an overall picture of the weather across theUnited States. [Figure 11-10]

This type of chart typically displays major fronts orareas of high and low pressure. The weather depictionchart also provides a graphic display of IFR, VFR, andMVFR (marginal VFR) weather. Areas of IFR conditions (ceilings less than 1,000 feet and visibilityless than 3 miles) are shown by a hatched area outlinedby a smooth line. MVFR regions (ceilings 1,000 to3,000 feet, visibility 3 to 5 miles) are shown by a

Figure 11-9. Sample station model and weather chart symbols.

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non-hatched area outlined by a smooth line. Areas ofVFR (no ceiling or ceiling greater than 3,000 feet and visibility greater than 5 miles) are not outlined.

Weather depiction charts show a modified stationmodel that provides sky conditions in the form of totalsky cover, cloud height or ceiling, weather, andobstructions to visibility, but does not include winds orpressure readings like the surface analysis chart. Abracket ( ] ) symbol to the right of the station indicatesthe observation was made by an automated station. Adetailed explanation of a station model is depicted inthe previous discussion of surface analysis charts.

RADAR SUMMARY CHARTA radar summary chart is a graphically depicted collection of radar weather reports (SDs). [Figure 11-11] The chart is published hourly at 35 minutes pastthe hour. It displays areas of precipitation as well as information regarding the characteristics of the precipitation. [Figure 11-12] A radar summary chartincludes:

• No information—If information is not reported,the chart will say “NA.” If no echoes aredetected, the chart will say “NE.”

• Precipitation intensity contours—Intensity canbe described as one of six levels and is shown onthe chart by three contour intervals.

• Height of tops—The heights of the echo tops aregiven in hundreds of feet MSL.

• Movement of cells—Individual cell movementis indicated by an arrow pointing in the directionof movement. The speed of movement in knots isthe number at the top of the arrow head. “LM”indicates little movement.

• Type of precipitation—The type of precipitationis marked on the chart using specific symbols.These symbols are not the same as used on theMETAR charts.

• Echo configuration—Echoes are shown asbeing areas, cells, or lines.

• Weather watches—Severe weather watch areasfor tornadoes and severe thunderstorms aredepicted by boxes outlined with heavy dashedlines.

The radar summary chart is a valuable tool for preflightplanning. It does, however, contain several limitationsfor the usage of the chart. This chart depicts only areasof precipitation. It will not show areas of clouds andfog with no appreciable precipitation, or the height ofthe tops and bases of the clouds. Radar summary chartsare a depiction of current precipitation and should beused in conjunction with current METAR and weatherforecasts.

Figure 11-10. Weather depiction chart.

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Figure 11-11. Radar summary chart.

Figure 11-12. Intensity levels and contours, and precipitation type symbols.

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SIGNIFICANT WEATHER PROGNOSTICCHARTS

Significant Weather Prognostic Charts are available forlow-level significant weather from the surface toFL240 (24,000 feet), also referred to as the 400 millibar level, and high-level significant weather fromFL250 to FL600 (25,000 to 60,000 feet). The primaryconcern of this discussion is the low-level significantweather prognostic chart.

The low-level chart comes in two forms: the 12- and24-hour forecast chart, and the 36 and 48 surface onlyforecast chart. The first chart is a four-panel chart thatincludes 12- and 24-hour forecasts for significantweather and surface weather. Charts are issued fourtimes a day at 0000Z, 0600Z, 1200Z, and 1800Z. Thevalid time for the chart is printed on the lower left-handcorner of each panel.

The upper two panels show forecast significantweather, which may include nonconvective turbulence,freezing levels, and IFR or MVFR weather. Areas ofmoderate or greater turbulence are enclosed in dashedlines. Numbers within these areas give the height of theturbulence in hundreds of feet MSL. Figures below theline show the anticipated base, while figures above theline show the top of the zone of turbulence. Also shownon this panel are areas of VFR, IFR, and MVFR. IFRareas are enclosed by solid lines, MVFR areas areenclosed by scalloped lines, and the remaining, unenclosed area is designated VFR. Zigzag lines andthe letters “SFC” indicate freezing levels in that area

are at the surface. Freezing level height contours forthe highest freezing level are drawn at 4,000-foot intervals with dashed lines.

The lower two panels show the forecast surfaceweather and depicts the forecast locations and characteristics of pressure systems, fronts, and precipitation. Standard symbols are used to show frontsand pressure centers. Direction of movement of thepressure center is depicted by an arrow. The speed, inknots, is shown next to the arrow. In addition, areas offorecast precipitation and thunderstorms are outlined.Areas of precipitation that are shaded indicate at leastone-half of the area is being affected by the precipita-tion. Unique symbols indicate the type of precipitationand the manner in which it occurs.

Figure 11-13 depicts a typical significant weather prognostic chart as well as the symbols typically usedto depict precipitation. Prognostic charts are an excellent source of information for preflight planning;however, this chart should be viewed in light of currentconditions and specific local area forecasts.

The 36- and 48-hour significant weather prognosticchart is an extension of the 12- and 24-hour forecast. Itprovides information regarding only surface weatherforecasts and includes a discussion of the forecast. Thischart is issued only two times a day. It typically contains forecast positions and characteristics of pressure patterns, fronts, and precipitation. An exampleof a 36- and 48-hour surface prognostic chart is shownin figure 11-14.

Figure 11-13. Significant weather prognostic chart.

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Figure 11-14. 36- and 48-hour surface prognostic chart.

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12-1

Each time a pilot operates an airplane, the flight nor-mally begins and ends at an airport. An airport maybe a small sod field or a large complex utilized by aircarriers. This chapter discusses airport operationsand identifies features of an airport complex, as wellas provides information on operating on or in thevicinity of an airport.

TYPES OF AIRPORTSThere are two types of airports.

• Controlled Airport

• Uncontrolled Airport

CONTROLLED AIRPORTA controlled airport has an operating control tower. Airtraffic control (ATC) is responsible for providing forthe safe, orderly, and expeditious flow of air traffic atairports where the type of operations and/or volume oftraffic requires such a service. Pilots operating from acontrolled airport are required to maintain two-wayradio communication with air traffic controllers, and toacknowledge and comply with their instructions.

Pilots must advise ATC if they cannot comply with theinstructions issued and request amended instructions.A pilot may deviate from an air traffic instruction in anemergency, but must advise ATC of the deviation assoon as possible.

UNCONTROLLED AIRPORTAn uncontrolled airport does not have an operatingcontrol tower. Two-way radio communications are notrequired, although it is a good operating practice forpilots to transmit their intentions on the specified fre-quency for the benefit of other traffic in the area. Figure12-1 lists recommended communication procedures.

More information on radio communications will bediscussed later in this chapter.

SOURCES FOR AIRPORT DATAWhen a pilot flies into a different airport, it isimportant to review the current data for that airport.This data can provide the pilot with information,such as communication frequencies, services avail-able, closed runways, or airport construction. Threecommon sources of information are:

• Aeronautical Charts

• Airport/Facility Directory (A/FD)

• Notices to Airmen (NOTAMs)

AERONAUTICAL CHARTSAeronautical charts provide specific information onairports. Chapter 14 contains an excerpt from an aero-nautical chart and an aeronautical chart legend, whichprovides guidance on interpreting the information onthe chart.

AIRPORT/FACILITY DIRECTORY The Airport/Facility Directory (A/FD) provides themost comprehensive information on a given airport. Itcontains information on airports, heliports, and sea-plane bases that are open to the public. The A/FDs arecontained in seven books, which are organized byregions. These A/FDs are revised every 8 weeks.Figure 12-2 contains an excerpt from a directory. For acomplete listing of information provided in an A/FDand how the information may be decoded, refer to the“Directory Legend Sample” located in the front of eachA/FD.

In the back of each A/FD, there is information such asspecial notices, parachute jumping areas, and facility

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FACILITY ATAIRPORT

FREQUENCY USECOMMUNICATION/BROADCAST PROCEDURES

OUTBOUND INBOUNDPRACTICE

INSTRUMENTAPPROACH

UNICOM(No Tower or FSS)

Communicate with UNICOM station on publishedCTAF frequency (122.7, 122.8, 122.725, 122.975,or 123.0). If unable to contact UNICOM station,use self-announce procedures on CTAF.

Before taxiing andbefore taxiing on therunway for departure.

10 miles out.Entering downwind,base, and final.Leaving the runway.

No Tower, FSS,or UNICOM

Self-announce on MULTICOM frequency 122.9 Departing finalapproach fix(name) or onfinal approachsegment inbound.

Approachcompleted/terminated.

No Tower in operation,FSS open

Communicate with FSS on CTAF frequency.

FSS closed(No Tower)

Self-announce on CTAF.

Self-announce on CTAF.Tower or FSSnot in operation

Before taxiing andbefore taxiing on therunway for departure.

Before taxiing andbefore taxiing on therunway for departure.

Before taxiing andbefore taxiing on therunway for departure.

Before taxiing andbefore taxiing on therunway for departure.

10 miles out.Entering downwind,base, and final.Leaving the runway.

10 miles out.Entering downwind,base, and final.Leaving the runway.

10 miles out.Entering downwind,base, and final.Leaving the runway.

10 miles out.Entering downwind,base, and final.Leaving the runway.

Figure 12-1. Recommended communication procedures.

Figure 12-2. Airport/Facility Directory excerpt.

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telephone numbers. It would be helpful to review anA/FD to become familiar with the information itcontains.

NOTICES TO AIRMENNotices to Airmen (NOTAMs) provide the most currentinformation available. They provide time-critical infor-mation on airports and changes that affect the nationalairspace system and are of concern to instrument flightrule (IFR) operations. NOTAM information is classifiedinto three categories. These are NOTAM-D or distant,NOTAM-L or local, and flight data center (FDC)NOTAMs. NOTAM-Ds are attached to hourly weatherreports and are available at flight service stations(AFSS/FSS). NOTAM-Ls include items of a local nature,such as taxiway closures or construction near a runway.These NOTAMs are maintained at the FSS nearest theairport affected. NOTAM-Ls must be requested from anFSS other than the one nearest the local airport for whichthe NOTAM was issued. FDC NOTAMs are issued bythe National Flight Data Center and contain regulatoryinformation, such as temporary flight restrictions or anamendment to instrument approach procedures. TheNOTAM-Ds and FDC NOTAMs are contained in theNotices to Airmen publication, which is issued every 28days. Prior to any flight, pilots should check for anyNOTAMs that could affect their intended flight.

AIRPORT MARKINGS AND SIGNSThere are markings and signs used at airports, whichprovide directions and assist pilots in airport opera-tions. Some of the most common markings and signswill be discussed. Additional information may be foundin the Aeronautical Information Manual (AIM).

RUNWAY MARKINGSRunway markings vary depending on the type of oper-ations conducted at the airport. Figure 12-3 shows arunway that is approved as a precision instrumentapproach runway and also shows some other commonrunway markings. A basic VFR runway may only havecenterline markings and runway numbers.

Since aircraft are affected by the wind during takeoffsand landings, runways are laid out according to thelocal prevailing winds. Runway numbers are in refer-ence to magnetic north. Certain airports have two oreven three runways laid out in the same direction.These are referred to as parallel runways and are distin-guished by a letter being added to the runway number.Examples are runway 36L (left), 36C (center), and 36R(right).

Another feature of some runways is a displaced thresh-old. A threshold may be displaced because of anobstruction near the end of the runway. Although this

portion of the runway is not to be used for landing, itmay be available for taxiing, takeoff, or landing rollout.

Some airports may have a blast pad/stopway area. Theblast pad is an area where a propeller or jet blast candissipate without creating a hazard. The stopway areais paved in order to provide space for an airplane todecelerate and stop in the event of an aborted takeoff.These areas cannot be used for takeoff or landing.

TAXIWAY MARKINGSAirplanes use taxiways to transition from parkingareas to the runway. Taxiways are identified by a con-tinuous yellow centerline stripe. A taxiway mayinclude edge markings to define the edge of the taxi-way. This is usually done when the taxiway edge doesnot correspond with the edge of the pavement. If anedge marking is a continuous line, the paved shoulderis not intended to be used by an airplane. If it is adashed marking, an airplane may use that portion ofthe pavement. Where a taxiway approaches a runway,there may be a holding position marker. These consistof four yellow lines (two solid and two dashed). Thesolid lines are where the airplane is to hold. At somecontrolled airports, holding position markings may befound on a runway. They are used when there areintersecting runways, and air traffic control issuesinstructions such as “cleared to land—hold short ofrunway 30.”

OTHER MARKINGSSome of the other markings found on the airportinclude vehicle roadway markings, VOR receivercheckpoint markings, and non-movement area bound-ary markings.

Vehicle roadway markings are used when necessary todefine a pathway for vehicle crossing areas that are alsointended for aircraft. These markings usually consist ofa solid white line to delineate each edge of the roadwayand a dashed line to separate lanes within the edges ofthe roadway.

A VOR receiver checkpoint marking consists of apainted circle with an arrow in the middle. The arrow isaligned in the direction of the checkpoint azimuth. Thisallows pilots to check aircraft instruments with naviga-tional aid signals.

A non-movement area boundary marking delineates amovement area under air traffic control. These mark-ings are yellow and located on the boundary betweenthe movement and non-movement area. They normallyconsist of two yellow lines (one solid and one dashed).

AIRPORT SIGNSThere are six types of signs that may be found at air-ports. The more complex the layout of an airport, the

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more important the signs become to pilots. Figure 12-4shows examples of signs, their purpose, and appropri-ate pilot action. The six types of signs are:

• Mandatory Instruction Signs—have a redbackground with a white inscription. These signsdenote an entrance to a runway, a critical area, ora prohibited area.

• Location Signs—are black with yellow inscrip-tion and a yellow border and do not have arrows.They are used to identify a taxiway or runwaylocation, to identify the boundary of the runway,

or identify an instrument landing system (ILS)critical area.

• Direction Signs—have a yellow backgroundwith black inscription. The inscription identifiesthe designation of the intersecting taxiway(s)leading out of an intersection.

• Destination Signs—have a yellow backgroundwith black inscription and also contain arrows.These signs provide information on locatingthings, such as runways, terminals, cargo areas,and civil aviation areas.

19

A

A

4

LEGENDIn-Pavement Runway Guard Lights

Elevated Runway Guard Lights

Stop BarCenterline/Lead-On Lights

Clearance Bar Lights

Position Marking4

Stop Bar/ILS Hold

VehicleLanes

(Zipper Style)

SurfacePaintedRunwayMarking

Taxiway EdgeMarking

(Do Not Cross)

Taxiway/Taxiway

HoldMarking

HoldMarkingFor LandAnd Hold

ShortOperations

Term

inal}

Non-Movement Area

Figure 12-3. Selected airport markings and surface lighting.

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• Information Signs—have a yellow backgroundwith black inscription. These signs are used toprovide the pilot with information on such thingsas areas that cannot be seen from the controltower, applicable radio frequencies, and noiseabatement procedures. The airport operator deter-mines the need, size, and location of these signs.

• Runway Distance Remaining Signs—have ablack background with white numbers. Thenumbers indicate the distance of the remainingrunway in thousands of feet.

AIRPORT LIGHTINGThe majority of airports have some type of lightingfor night operations. The variety and type of lightingsystems depends on the volume and complexity ofoperations at a given airport. Airport lighting is stan-dardized so that airports use the same light colors forrunways and taxiways.

AIRPORT BEACONAirport beacons help a pilot identify an airport at night.The beacons are operated from dusk till dawn andsometimes they are turned on if the ceiling is less than1,000 feet and/or the ground visibility is less than 3statute miles (visual flight rules minimums). However,there is no requirement for this, so a pilot has theresponsibility of determining if the weather is VFR.

The beacon has a vertical light distribution to make itmost effective from 1-10° above the horizon, althoughit can be seen well above or below this spread. The bea-con may be an omnidirectional capacitor-dischargedevice, or it may rotate at a constant speed, which pro-duces the visual effect of flashes at regular intervals.The combination of light colors from an airport beaconindicates the type of airport. [Figure 12-5]

Some of the most common beacons are:

• Flashing white and green for civilian landairports.

• Flashing white and yellow for a water airport.

• Flashing white, yellow, and green for a heliport.

• Two quick white flashes followed by a greenflash identifies a military airport.

4-22

8-APCH

ILS

4

B

22

J

L

22

MIL

Hold short of runway on taxiway

Exit boundary of ILS critical area

Defines directions to takeoff runways

Defines directions for arriving aircraft

Provides remaining runway lengthin 1,000 feet increments

Indicates taxiway does not continue

Defines direction & designation of exit taxiwayfrom runway

Runway Exit:.

Defines direction & designation of intersectingtaxiway(s)

Taxiway Direction:

Hold short of aircraft on approach

Hold short of ILS approach critical area

Identifies paved areas where aircraft entry isprohibited

Identifies taxiway on which aircraft is located

Identifies runway on which aircraft is located

Taxiway/Runway Hold Position:

Runway Approach Hold Position:

ILS Critical Area Hold Position:

Exit boundary of runway protected areas

Runway Safety Area/Obstacle FreeZone Boundary:

ILS Critical Area Boundary:

No Entry:

Taxiway Location:

Outbound Destination:

Inbound Destination:

Taxiway Ending MarkerRunway Location:

Runway Distance Remaining

TYPE OF SIGN AND ACTION OR PURPOSETYPE OF SIGN AND ACTION OR PURPOSE

AIRPORT SIGN SYSTEMS

26-8 Runway/Runway Hold Position:

Hold short of intersecting runway

A LGDirection Sign Array:

Identifies location in conjunction withmultiple intersecting taxiways

Figure 12-4. Airport signs.

WhiteWhite

White

GreenGreen

Figure 12-5. Airport rotating beacons.

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12-6

APPROACH LIGHT SYSTEMSApproach light systems are primarily intended toprovide a means to transition from instrument flightto visual flight for landing. The system configura-tion depends on whether the runway is a precision ornonprecision instrument runway. Some systemsinclude sequenced flashing lights, which appear tothe pilot as a ball of light traveling toward the run-way at high speed. Approach lights can also aidpilots operating under VFR at night.

VISUAL GLIDESLOPE INDICATORSVisual glideslope indicators provide the pilot withglidepath information that can be used for day or nightapproaches. By maintaining the proper glidepath asprovided by the system, a pilot should have adequateobstacle clearance and should touch down within aspecified portion of the runway.

VISUAL APPROACH SLOPE INDICATORVisual approach slope indicator (VASI) installationsare the most common visual glidepath systems in use.The VASI provides obstruction clearance within 10°of the runway extended runway centerline, and to 4nautical miles (NM) from the runway threshold.

A VASI consists of light units arranged in bars. Thereare 2-bar and 3-bar VASIs. The 2-bar VASI has nearand far light bars and the 3-bar VASI has near, middle,and far light bars. Two-bar VASI installations provideone visual glidepath which is normally set at 3°. The3-bar system provides two glidepaths with the lowerglidepath normally set at 3° and the upper glidepathone-fourth degree above the lower glidepath.

The basic principle of the VASI is that of color differen-tiation between red and white. Each light unit projects abeam of light having a white segment in the upper partof the beam and a red segment in the lower part of thebeam. The lights are arranged so the pilot will see thecombination of lights shown in figure 12-6 to indicatebelow, on, or above the glidepath.

OTHER GLIDEPATH SYSTEMSA precision approach path indicator (PAPI) uses lightssimilar to the VASI system except they are installed ina single row, normally on the left side of the runway.[Figure 12-7]

A tri-color system consists of a single light unit pro-jecting a three-color visual approach path. A below theglidepath indication is red, on the glidepath color isgreen, and above the glidepath is indicated by amber.When descending below the glidepath, there is a smallarea of dark amber. Pilots should not mistake this areafor an “above the glidepath” indication. [Figure 12-8]

There are also pulsating systems, which consist of asingle light unit projecting a two-color visual approachpath. A below the glidepath indication is shown by asteady red light, slightly below is indicated by pulsat-ing red, on the glidepath is indicated by a steady whitelight, and a pulsating white light indicates above theglidepath. [Figure 12-9]

RUNWAY LIGHTINGThere are various lights that identify parts of the runwaycomplex. These assist a pilot in safely making a takeoffor landing during night operations.

RUNWAY END IDENTIFIER LIGHTSRunway end identifier lights (REIL) are installed atmany airfields to provide rapid and positive identifi-

High(More Than

3.5 Degrees)

Slightly High(3.2 Degrees)

On Glidepath(3 Degrees)

Slightly Low(2.8 Degrees)

Low(Less Than

2.5 Degrees)

Below Glidepath

Near Bar

Far Bar

On Glidepath Above Glidepath

Figure 12-6. 2-Bar VASI system.

Figure 12-7. Precision approach path indicator.

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cation of the approach end of a particular runway. Thesystem consists of a pair of synchronized flashinglights located laterally on each side of the runwaythreshold. REILs may be either omnidirectional orunidirectional facing the approach area.

RUNWAY EDGE LIGHTSRunway edge lights are used to outline the edges ofrunways at night or during low visibility conditions.These lights are classified according to the intensitythey are capable of producing. They are classified ashigh intensity runway lights (HIRL), medium intensityrunway lights (MIRL), or low intensity runway lights(LIRL). The HIRL and MIRL have variable intensitysettings. These lights are white, except on instrumentrunways, where amber lights are used on the last 2,000feet or half the length of the runway, whichever is less.The lights marking the end of the runway are red.

IN-RUNWAY LIGHTINGTouchdown zone lights (TDZL), runway centerlinelights (RCLS), and taxiway turnoff lights are installed

on some precision runways to facilitate landing underadverse visibility conditions. TDZLs are two rows oftransverse light bars disposed symmetrically about therunway centerline in the runway touchdown zone.RCLS consists of flush centerline lights spaced at 50foot intervals beginning 75 feet from the landingthreshold. Taxiway turnoff lights are flush lights, whichemit a steady green color.

CONTROL OF AIRPORT LIGHTINGAirport lighting is controlled by air traffic controllersat controlled airports. At uncontrolled airports, thelights may be on a timer, or where an FSS is located atan airport, the FSS personnel may control the light-ing. A pilot may request various light systems beturned on or off and also request a specified intensity,if available, from ATC or FSS personnel. At selecteduncontrolled airports, the pilot may control the light-ing by using the radio. This is done by selecting aspecified frequency and clicking the radio micro-phone. For information on pilot controlled lighting at

Amber

Green

Red

AmberAbove Glidepath

On Glidepath

Below Glidepath

Figure 12-8.Tri-color visual approach slope indicator.

PULSATING WHITEPULSATING WHITE

PULSATING RED

STEADY REDSlightly Below Glidepath

Below Glidepath

Threshold

PULSATING WHITE

Above Glidepath STEADY WHITE

On Glidepath

Figure 12-9. Pulsating visual approach slope indicator.

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various airports, refer to the Airport/FacilityDirectory. [Figure 12-10]

TAXIWAY LIGHTSOmnidirectional taxiway lights outline the edges of thetaxiway and are blue in color. At many airports, theseedge lights may have variable intensity settings thatmay be adjusted by an air traffic controller whendeemed necessary or when requested by the pilot.Some airports also have taxiway centerline lights thatare green in color.

OBSTRUCTION LIGHTSObstructions are marked or lighted to warn pilots oftheir presence during daytime and nighttime condi-tions. Obstruction lighting can be found both on andoff an airport to identify obstructions. They may bemarked or lighted in any of the following conditions.

• Red Obstruction Lights—either flash or emit asteady red color during nighttime operations, andthe obstructions are painted orange and white fordaytime operations.

• High Intensity White Obstruction Light—flashes high intensity white lights during thedaytime with the intensity reduced for nighttime.

• Dual Lighting—is a combination of flashing redbeacons and steady red lights for nighttime oper-ation, and high intensity white lights for daytimeoperations.

WIND DIRECTION INDICATORSIt is important for a pilot to know the direction of thewind. At facilities with an operating control tower,this information is provided by ATC. Informationmay also be provided by FSS personnel located at aparticular airport or by requesting information on acommon traffic advisory frequency (CTAF) at air-ports that have the capacity to receive and broadcaston this frequency.

When none of these services is available, it is possibleto determine wind direction and runway in use byvisual wind indicators. A pilot should check these windindicators even when information is provided on theCTAF at a given airport because there is no assurancethat the information provided is accurate.

Wind direction indicators include a wind sock, windtee, or tetrahedron. These are usually located in a cen-tral location near the runway and may be placed in thecenter of a segmented circle, which will identify thetraffic pattern direction, if it is other than the standardleft-hand pattern. [Figures 12-11 and 12-12]

The wind sock is a good source of information since itnot only indicates wind direction, but allows the pilotto estimate the wind velocity and gusts or factor. Thewind sock extends out straighter in strong winds andwill tend to move back and forth when the wind isgusty. Wind tees and tetrahedrons can swing freely, andwill align themselves with the wind direction. The windtee and tetrahedron can also be manually set to alignwith the runway in use; therefore, a pilot should alsolook at the wind sock, if available.

RADIO COMMUNICATIONSOperating in and out of a controlled airport, as wellas in a good portion of the airspace system, requiresthat an aircraft have two-way radio communicationcapability. For this reason, a pilot should be knowl-edgeable of radio station license requirements andradio communications equipment and procedures.

RADIO LICENSEThere is no license requirement for a pilot operatingin the United States; however, a pilot who operatesinternationally is required to hold a restrictedradiotelephone permit issued by the FederalCommunications Commission (FCC). There is alsono station license requirement for most general avia-tion aircraft operating in the United States. A stationlicense is required however for an aircraft which isoperating internationally, which uses other than a veryhigh frequency (VHF) radio, and which meets othercriteria.

RADIO EQUIPMENTIn general aviation, the most common types of radiosare VHF. A VHF radio operates on frequenciesbetween 118.0 and 136.975 and is classified as 720 or760 depending on the number of channels it canaccommodate. The 720 and 760 uses .025 spacing(118.025, 118.050) with the 720 having a frequencyrange up to 135.975 and the 760 going up to 136.975.VHF radios are limited to line of sight transmissions;

7 times within 5seconds

5 times within 5seconds

3 times within 5seconds

Highest intensity available

Medium or lower intensity(Lower REIL or REIL off)

Lowest intensity available(Lower REIL or REIL off)

KEY MIKE FUNCTION

Figure 12-10. Radio control runway lighting.

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therefore, aircraft at higher altitudes are able to trans-mit and receive at greater distances.

Using proper radio phraseology and procedures willcontribute to a pilot’s ability to operate safely andefficiently in the airspace system. A review of thePilot/Controller Glossary contained in theAeronautical Information Manual (AIM) will assist apilot in the use and understanding of standard termi-nology. The AIM also contains many examples ofradio communications, which should be helpful.

The International Civil Aviation Organization (ICAO)has adopted a phonetic alphabet, which should be usedin radio communications. When communicating with

ATC, pilots should use this alphabet to identify theiraircraft. [Figure 12-13]

LOST COMMUNICATION PROCEDURESIt is possible that a pilot might experience a malfunc-tion of the radio. This might cause the transmitter,receiver, or both to become inoperative. If a receiverbecomes inoperative and a pilot needs to land at a con-trolled airport, it is advisable to remain outside orabove Class D airspace until the direction and flow oftraffic is determined. A pilot should then advise thetower of the aircraft type, position, altitude, andintention to land. The pilot should continue, enter thepattern, report a position as appropriate, and watch

TETRAHEDRON

WIND TEE

WIND SOCK OR CONE

Application of Traffic PatternIndicators

Legend:Recommended Standard Left-HandTraffic pattern (depicted)(Standard Right-hand TrafficPattern would be the opposite)

DOWNWIND

DEPARTURE

FINAL

DEPARTURE

BASE

DEPARTURE

RUNWAY

HAZARD ORPOPULATED AREA

LANDING DIRECTIONINDICATOR

WINDCONE

LANDING RUNWAY(OR LANDING STRIP)INDICATORS

SEGMENTED CIRCLE

TRAFFIC PATTERN INDICATORS

CROSS- WIND

ENTRY

Figure 12-12. Segmented circle and airport traffic pattern.

Figure 12-11. Wind direction indicators.

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for light signals from the tower. Light signal colorsand their meanings are contained in figure 12-14.

If the transmitter becomes inoperative, a pilot shouldfollow the previously stated procedures and also moni-tor the appropriate air traffic control frequency. Duringdaylight hours air traffic control transmissions may beacknowledged by rocking the wings, and at night byblinking the landing light.

When both receiver and transmitter are inoperative, thepilot should remain outside of Class D airspace untilthe flow of traffic has been determined and then enterthe pattern and watch for light signals.

If a radio malfunctions prior to departure, it is advisableto have it repaired, if possible. If this is not possible, a

call should be made to air traffic control and the pilotshould request authorization to depart without two-wayradio communications. If authorization is given todepart, the pilot will be advised to monitor the appro-priate frequency and/or watch for light signals asappropriate.

AIR TRAFFIC CONTROL SERVICESBesides the services provided by FSS as discussed inChapter 11, there are numerous other services providedby ATC. In many instances a pilot is required to have con-tact with air traffic control, but even when not required, apilot will find it helpful to request their services.

PRIMARY RADARRadar is a method whereby radio waves are transmittedinto the air and are then received when they have beenreflected by an object in the path of the beam. Range is

AlfaBravoCharlieDeltaEchoFoxtrotGolfHotelIndiaJulietKiloLimaMikeNovemberOscarPapaQuebecRomeoSierraTangoUniformVictorWhiskeyXrayYankeeZuluOneTwoThreeFourFiveSixSevenEightNineZero

(AL-FAH)(BRAH-VOH)(CHAR-LEE) OR (SHAR-LEE)(DELL-TAH)(ECK-OH)(FOKS-TROT)(GOLF)(HOH-TEL)(IN-DEE-AH)(JEW-LEE-ETT)(KEY-LOH)(LEE-MAH)(MIKE)(NO-VEM-BER)(OSS-CAH)(PAH-PAH)(KEH-BECK)(ROW-ME-OH)(SEE-AIR-RAH)(TANG-GO)(YOU-NEE-FORM) OR (OO-NEE-FORM)(VIK-TAH)(WISS-KEY)(ECKS-RAY)(YANG-KEY)(ZOO-LOO)(WUN)(TOO)(TREE)(FOW-ER)(FIFE)(SIX)(SEV-EN)(AIT)(NIN-ER)(ZEE-RO)

TELEPHONY PHONIC (PRONUNCIATION)

ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890

CHARACTER MORSE CODE

•--•••-•-•-•••••-•--••••••••----•-•-••---•---•--•--•-•-••••-••-•••-•---••--•----•••----••---•••--••••-•••••-••••--•••---••----•-----

Figure 12-13. Phonetic alphabet.

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determined by measuring the time it takes (at the speedof light) for the radio wave to go out to the object andthen return to the receiving antenna. The direction of adetected object from a radar site is determined by theposition of the rotating antenna when the reflected por-tion of the radio wave is received.

Modern radar is very reliable and there are seldomoutages. This is due to reliable maintenance andimproved equipment. There are, however, some limi-tations which may affect air traffic control servicesand prevent a controller from issuing advisories con-cerning aircraft which are not under their control andcannot be seen on radar.

The characteristics of radio waves are such that theynormally travel in a continuous straight line unless theyare “bent” by atmospheric phenomena such as temper-ature inversions, reflected or attenuated by denseobjects such as heavy clouds and precipitation, orscreened by high terrain features.

AIR TRAFFIC CONTROL RADARBEACON SYSTEMThe air traffic control radar beacon system (ATCRBS) isoften referred to as “secondary surveillance radar.” Thissystem consists of three components and helps in allevi-ating some of the limitations associated with primaryradar. The three components are an interrogator,transponder, and radarscope. The advantages of ATCRBSare the reinforcement of radar targets, rapid target identi-fication, and a unique display of selected codes.

TRANSPONDERThe transponder is the airborne portion of the second-ary surveillance radar system and a system with whicha pilot should be familiar. The ATCRBS cannot displaythe secondary information unless an aircraft isequipped with a transponder. A transponder is alsorequired to operate in certain controlled airspace.Airspace is discussed in chapter 13.

A transponder code consists of four numbers fromzero to seven (4,096 possible codes). There are somestandard codes, or ATC may issue a four-digit code toan aircraft. When a controller requests a code or func-tion on the transponder, the word “squawk” may beused. Figure 12-15 lists some standard transponderphraseology.

RADAR TRAFFIC INFORMATION SERVICERadar equipped air traffic control facilities provideradar assistance to VFR aircraft provided the aircraftcan communicate with the facility and are within radarcoverage. This basic service includes safety alerts, traf-fic advisories, limited vectoring when requested, andsequencing at locations where this procedure has beenestablished. In addition to basic radar service, terminalradar service area (TRSA) has been implemented atcertain terminal locations. The purpose of this serviceis to provide separation between all participating VFRaircraft and all IFR aircraft operating within the TRSA.Class C service provides approved separation betweenIFR and VFR aircraft, and sequencing of VFR aircraftto the primary airport. Class B service providesapproved separation of aircraft based on IFR, VFR,

LIGHT GUN SIGNALS

COLOR AND TYPE OF SIGNAL

MOVEMENT OF VEHICLES,EQUIPMENT AND PERSONNEL

AIRCRAFT ONTHE GROUND

AIRCRAFTIN FLIGHT

STEADYGREEN

FLASHINGGREEN

STEADY RED

FLASHING RED

FLASHING WHITE

ALTERNATINGRED AND GREEN

Cleared to cross,proceed or go

Cleared for takeoff Cleared to land

Not applicable Cleared for taxi Return for landing(to be followed by steadygreen at the proper time)

STOP STOP Give way to other aircraftand continue circling

Clear the taxiway/runway Taxi clear of therunway in use

Airport unsafe, donot land

Return to starting point on airport Return to starting point on airport

Not applicable

Exercise Extreme Caution!!!! Exercise Extreme Caution!!!! Exercise Extreme Caution!!!!

Figure 12-14. Light gun signals.

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and/or weight, and sequencing of VFR arrivals to theprimary airport(s).

ATC issues traffic information based on observed radartargets. The traffic is referenced by azimuth from theaircraft in terms of the 12-hour clock. Also the distancein nautical miles, direction in which the target is mov-ing, and the type and altitude of the aircraft, if known,are given. An example would be: “Traffic 10 o’clock 5miles east bound, Cessna 152, 3,000 feet.” The pilotshould note that traffic position is based on the aircrafttrack, and that wind correction can affect the clockposition at which a pilot locates traffic. [Figure 12-16]

WAKE TURBULENCEAll aircraft generate a wake while in flight. This distur-bance is caused by a pair of counter-rotating vorticestrailing from the wingtips. The vortices from larger air-craft pose problems to encountering aircraft. The wake ofthese aircraft can impose rolling moments exceeding theroll-control authority of the encountering aircraft. Also,the turbulence generated within the vortices can damage

aircraft components and equipment if encountered atclose range. For this reason, a pilot must envision thelocation of the vortex wake and adjust the flightpathaccordingly.

During ground operations and during takeoff, jet-engine blast (thrust stream turbulence) can causedamage and upsets at close range. For this reason,pilots of small aircraft should consider the effects of

TRACK TRACK

Traffic information would be issued to the pilot of aircraft "A" as 12 o'clock. The actual position of the traffic as seen by the pilot of aircraft "A" would be 2 o'clock. Traffic information issued to aircraft "B" would also be given as 12 o'clock, but in this case, the pilot of "B" would see traffic at 10 o'clock.

Figure 12-16.Traffic advisories.

SQUAWK (number)

IDENT

SQUAWK (number) and IDENT

SQUAWK STANDBY

SQUAWK LOW/NORMAL

SQUAWK ALTITUDE

STOP ALTITUDE SQUAWK

STOP SQUAWK (mode in use)

STOP SQUAWK

SQUAWK MAYDAY

SQUAWK VFR

Operate radar beacon transponder on designated code in MODE A/3

Engage the "IDENT" feature (military I/P) of the transponder.

Operate transponder on specified code in MODE A/3 and engagethe "IDENT" (military I/P) feature.

Switch transponder to standby position.

Operate transponder on low or normal sensitivity as specified.Transponder is operated in "NORMAL" position unless ATCspecifies "LOW" ("ON" is used instead of "NORMAL" as amaster control label on some types of transponders).

Activate MODE C with automatic altitude reporting.

Turn off altitude reporting switch and continue transmittingMODE C framing pulses. If your equipment does not have thiscapability, turn off MODE C.

Switch off specified mode. (Used for military aircraft when thecontroller is unaware of military service requirements for theaircraft to continue operation on another MODE.)

Switch off transponder.

Operate transponder in the emergency position (MODE A Code7700 for civil transponder. MODE 3 Code 7700 and emergencyfeature for military transponder.)

Operate radar beacon transponder on Code 1200 in the MODEA/3, or other appropriate VFR code.

RADAR BEACON PHRASEOLOGY

Figure 12-15.Transponder phraseology.

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jet-engine blast and maintain adequate separation.Also, pilots of larger aircraft should consider theeffects of their aircraft’s jet-engine blast on other air-craft and equipment on the ground.

VORTEX GENERATIONLift is generated by the creation of a pressure differentialover the wing surface. The lowest pressure occurs overthe upper wing surface, and the highest pressure underthe wing. This pressure differential triggers the rollup ofthe airflow aft of the wing resulting in swirling airmasses trailing downstream of the wingtips. After therollup is completed, the wake consists of two counter-rotating cylindrical vortices. Most of the energy is withina few feet of the center of each vortex, but pilots shouldavoid a region within about 100 feet of the vortex core.[Figure 12-17]

VORTEX STRENGTHThe strength of the vortex is governed by the weight,speed, and shape of the wing of the generating aircraft.The vortex characteristics of any given aircraft can alsobe changed by the extension of flaps or other wing con-figuration devices as well as by a change in speed. Thegreatest vortex strength occurs when the generating air-craft is heavy, clean, and slow.

VORTEX BEHAVIORTrailing vortices have certain behavioral characteristicsthat can help a pilot visualize the wake location and takeavoidance precautions.

Vortices are generated from the moment an aircraftleaves the ground, since trailing vortices are the by-product of wing lift. The vortex circulation is outward,upward, and around the wingtips when viewed fromeither ahead or behind the aircraft. Tests have shownthat vortices remain spaced a bit less than a wingspanapart, drifting with the wind, at altitudes greater than awingspan from the ground. Tests have also shown thatthe vortices sink at a rate of several hundred feet perminute, slowing their descent and diminishing instrength with time and distance behind the generatingaircraft. [Figure 12-18]

When the vortices of larger aircraft sink close to theground (within 100 to 200 feet), they tend to move lat-erally over the ground at a speed of 2 or 3 knots. Acrosswind will decrease the lateral movement of theupwind vortex and increase the movement of the down-wind vortex. A tailwind condition can move the vorticesof the preceding aircraft forward into the touchdownzone.

VORTEX AVOIDANCE PROCEDURES

• Landing behind a larger aircraft on the samerunway—stay at or above the larger aircraft’sapproach flightpath and land beyond its touch-down point.

• Landing behind a larger aircraft on a parallelrunway closer than 2,500 feet—consider thepossibility of drift and stay at or above the largeraircraft’s final approach flightpath and note itstouchdown point.

• Landing behind a larger aircraft on crossing run-way—cross above the larger aircraft’s flightpath.

Figure 12-17. Vortex generation.

Touchdown Rotation

Wake Ends Wake Begins

Figure 12-18. Vortex behavior.

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• Landing behind a departing aircraft on the samerunway—land prior to the departing aircraft’srotating point.

• Landing behind a larger aircraft on a crossingrunway—note the aircraft’s rotation point and ifpast the intersection, continue and land prior tothe intersection. If the larger aircraft rotates priorto the intersection, avoid flight below its flight-path. Abandon the approach unless a landing isensured well before reaching the intersection.

• Departing behind a large aircraft, rotate prior tothe large aircraft’s rotation point and climb aboveits climb path until turning clear of the wake.

• For intersection takeoffs on the same runway, bealert to adjacent larger aircraft operations, partic-ularly upwind of the runway of intended use. Ifan intersection takeoff clearance is received,avoid headings that will cross below the largeraircraft’s path.

• If departing or landing after a large aircraft execut-ing a low approach, missed approach, or touch andgo landing (since vortices settle and move laterallynear the ground, the vortex hazard may exist alongthe runway and in the flightpath, particularly in aquartering tailwind), it is prudent to wait 2 minutesprior to a takeoff or landing.

• En route it is advisable to avoid a path belowand behind a large aircraft, and if a large aircraftis observed above on the same track, change theaircraft position laterally and preferablyupwind.

COLLISION AVOIDANCETitle 14 of the Code of Federal Regulations (14 CFR)part 91 has established right-of-way rules, minimumsafe altitudes, and VFR cruising altitudes to enhanceflight safety. The pilot can contribute to collision avoid-ance by being alert and scanning for other aircraft. Thisis particularly important in the vicinity of an airport.

Effective scanning is accomplished with a series ofshort, regularly spaced eye movements that bring suc-cessive areas of the sky into the central visual field.Each movement should not exceed 10°, and eachshould be observed for at least 1 second to enabledetection. Although back and forth eye movementsseem preferred by most pilots, each pilot shoulddevelop a scanning pattern that is most comfortable andthen adhere to it to assure optimum scanning.

Even if entitled to the right-of-way, a pilot should giveway if it is felt another aircraft is too close.

CLEARING PROCEDURESThe following procedures and considerationsshould assist a pilot in collision avoidance undervarious situations.

• Before Takeoff—Prior to taxiing onto a runwayor landing area in preparation for takeoff, pilotsshould scan the approach area for possible land-ing traffic, executing appropriate maneuvers toprovide a clear view of the approach areas.

• Climbs and Descents—During climbs anddescents in flight conditions which permit visualdetection of other traffic, pilots should executegentle banks left and right at a frequency whichpermits continuous visual scanning of the air-space.

• Straight and Level—During sustained peri-ods of straight-and-level flight, a pilot shouldexecute appropriate clearing procedures atperiodic intervals.

• Traffic Patterns—Entries into traffic patternswhile descending should be avoided.

• Traffic at VOR Sites—Due to converging traffic,sustained vigilance should be maintained in thevicinity of VORs and intersections.

• Training Operations—Vigilance should bemaintained and clearing turns should be madeprior to a practice maneuver. During instruction,the pilot should be asked to verbalize the clearingprocedures (call out “clear left, right, above, andbelow”).

High-wing and low-wing aircraft have their respectiveblind spots. High-wing aircraft should momentarilyraise their wing in the direction of the intended turn andlook for traffic prior to commencing the turn. Low-wing aircraft should momentarily lower the wing.

RUNWAY INCURSION AVOIDANCEIt is important to give the same attention to operat-ing on the surface as in other phases of flights.Proper planning can prevent runway incursions andthe possibility of a ground collision. A pilot shouldbe aware of the airplane’s position on the surface atall times and be aware of other aircraft and vehicleoperations on the airport. At times controlled air-ports can be busy and taxi instructions complex. In

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this situation it may be advisable to write down taxiinstructions. The following are some practices tohelp prevent a runway incursion.

• Read back all runway crossing and/or holdinstructions.

• Review airport layouts as part of preflightplanning and before descending to land, andwhile taxiing as needed.

• Know airport signage.

• Review Notices to Airmen (NOTAM) for informa-tion on runway/taxiway closures and constructionareas.

• Request progressive taxi instructions from ATCwhen unsure of the taxi route.

• Check for traffic before crossing any RunwayHold Line and before entering a taxiway.

• Turn on aircraft lights and the rotating beacon orstrobe lights while taxing.

• When landing, clear the active runway as soon aspossible, then wait for taxi instructions beforefurther movement.

• Study and use proper phraseology in order tounderstand and respond to ground controlinstructions.

• Write down complex taxi instructions at unfamil-iar airports.

For more detailed information, refer to AdvisoryCircular (AC) 91-73, Part 91 Pilot and FlightcrewProcedures During Taxi Operations and Part 135Single-Pilot Operations.

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This chapter introduces the various classifications ofairspace and provides information on the requirementsto operate in such airspace. For further information,consult the Aeronautical Information Manual (AIM)and 14 CFR parts 71, 73, and 91.

The two categories of airspace are: regulatory and non-regulatory. Within these two categories there are fourtypes: controlled, uncontrolled, special use, and otherairspace.

Figure 13-1 presents a profile view of the dimen-sions of various classes of airspace. Figure 13-2gives the basic weather minimums for operating inthe different classes of airspace. Figure 13-3 lists theoperational and equipment requirements. It will behelpful to refer to these figures as this chapter isstudied. Also there are excerpts from sectional chartsin Chapter 14Navigation, that will show how air-space is depicted.

CONTROLLED AIRSPACEControlled airspace is a generic term that covers thedifferent classifications of airspace and defineddimensions within which air traffic control service isprovided in accordance with the airspace classifica-tion. Controlled airspace consists of:

• Class A

• Class B

• Class C

• Class D

• Class E

CLASS A AIRSPACEClass A airspace is generally the airspace from 18,000feet mean sea level (MSL) up to and including FL600,including the airspace overlying the waters within 12nautical miles (NM) of the coast of the 48 contiguousstates and Alaska. Unless otherwise authorized, alloperation in Class A airspace will be conducted underinstrument flight rules (IFR).

CLASS B AIRSPACEClass B airspace is generally the airspace from thesurface to 10,000 feet MSL surrounding the nation’sbusiest airports. The configuration of Class B airspaceis individually tailored to the needs of a particular areaand consists of a surface area and two or more layers.Some Class B airspace resembles an upside-downwedding cake. At least a private pilot certificate isrequired to operate in Class B airspace; however, thereis an exception to this requirement. Student pilots orrecreational pilots seeking private pilot certificationmay operate in the airspace and land at other thanspecified primary airports within the airspace if theyhave received training and had their logbook endorsedby a certified flight instructor in accordance with Title14 of the Code of Federal Regulations (14 CFR) part61.

CLASS C AIRSPACEClass C airspace generally extends from the surfaceto 4,000 feet above the airport elevation surroundingthose airports having an operational control tower,that are serviced by a radar approach control, andwith a certain number of IFR operations or passen-ger enplanements. This airspace is charted in feet

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13-2

NontoweredAirport 700 AGL

CLASS A

CLASS B

CLASS CCLASS D

1200 AGL

CLASS G CLASS G

CLASS E

CLASS G

FL 600MSL 18,000

14,500 MSL

MSL – mean sea level AGL – above ground level FL – flight level

Figure 13-1. Airspace profile.

BASIC VFR WEATHER MINIMUMS

Airspace Flight Visibility Distance from Clouds

Class A ......................................................................

Class B ......................................................................

Class C ......................................................................

Class D ......................................................................

Class E Less than 10,000 feet MSL ......................................

At or above 10,000 feet MSL .......................................

Not Applicable Not Applicable

3 statute miles Clear of Clouds

3 statute miles

3 statute miles

500 feet below1,000 feet above2,000 feet horizontal

500 feet below1,000 feet above2,000 feet horizontal

500 feet below1,000 feet above2,000 feet horizontal

3 statute miles

5 statute miles 1,000 feet below1,000 feet above1 statute mile horizontal

Class G 1,200 feet or less above the surface (regardless of MSL altitude). Day, except as provided in section 91.155(b). ...........

1 statute mile Clear of Clouds

Night, except as provided in section 91.155(b). ........... 3 statute miles 500 feet below1,000 feet above2,000 feet horizontal

More than 1,200 feet above the surface but less than10,000 feet MSL. Day ................................................................................

Night .............................................................................

More than 1,200 feet above the surface and at orabove 10,000 feet MSL. ..................................................

1 statute mile 500 feet below1,000 feet above2,000 feet horizontal

500 feet below1,000 feet above2,000 feet horizontal

3 statute miles

5 statute miles 1,000 feet below1,000 feet above1 statute mile horizontal

Figure 13-2. Visual flight rule weather minimums.

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MSL, and is generally of a 5 NM radius surface areathat extends from the surface to 4,000 feet above theairport elevation, and a 10 NM radius area thatextends from 1,200 feet to 4,000 feet above the air-port elevation. There is also an outer area with a 20NM radius, which extends from the surface to 4,000feet above the primary airport, and this area mayinclude one or more satellite airports.

CLASS D AIRSPACEClass D airspace generally extends from the surfaceto 2,500 feet above the airport elevation surround-ing those airports that have an operational controltower. The configuration of Class D airspace will betailored to meet the operational needs of the area.

CLASS E AIRSPACEClass E airspace is generally controlled airspace thatis not designated A, B, C, or D. Except for 18,000feet MSL, Class E airspace has no defined verticallimit, but rather it extends upward from either thesurface or a designated altitude to the overlying oradjacent controlled airspace.

UNCONTROLLED AIRSPACE

CLASS G AIRSPACEUncontrolled airspace or Class G airspace is theportion of the airspace that has not been designatedas Class A, B, C, D, or E. It is therefore designateduncontrolled airspace. Class G airspace extendsfrom the surface to the base of the overlying Class Eairspace. Although air traffic control (ATC) has noauthority or responsibility to control air traffic,

pilots should remember there are VFR minimumswhich apply to Class G airspace.

SPECIAL USE AIRSPACESpecial use airspace exists where activities mustbe confined because of their nature. In special useairspace, limitations may be placed on aircraft thatare not a part of the activities. Special use airspaceusually consists of:

• Prohibited Areas

• Restricted Areas

• Warning Areas

• Military Operation Areas

• Alert Areas

• Controlled Firing Areas

PROHIBITED AREASProhibited areas are established for security or otherreasons associated with the national welfare.Prohibited areas are published in the FederalRegister and are depicted on aeronautical charts.

RESTRICTED AREASRestricted areas denote the existence of unusual,often invisible hazards to aircraft such as artilleryfiring, aerial gunnery, or guided missiles. An aircraftmay not enter a restricted area unless permission hasbeen obtained from the controlling agency.Restricted areas are depicted on aeronautical chartsand are published in the Federal Register.

ClassAirspace

Entry Requirements Equipment Minimum PilotCertificate

A ATC Clearance IFR Equipped Instrument Rating

B ATC Clearance Two-Way Radio, Transponderwith Altitude Reporting Capability

Private—Except a student orrecreational pilot may operateat other than the primaryairport if seeking private pilotcertification and if regulatoryrequirements are met.

C Two-Way Radio CommunicationsPrior to Entry

Two-Way Radio, Transponderwith Altitude Reporting Capability

No Specific Requirement

D Two-Way Radio CommunicationsPrior to Entry

Two-Way Radio No Specific Requirement

No Specific Requirement No Specific Requirement

No Specific RequirementNo Specific Requirement

E

G

None for VFR

None

Figure 13-3. Requirements for airspace operations.

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WARNING AREASWarning areas consist of airspace which may containhazards to nonparticipating aircraft in internationalairspace. The activities may be much the same asthose for a restricted area. Warning areas are estab-lished beyond the 3-mile limit. Warning areas aredepicted on aeronautical charts.

MILITARY OPERATION AREASMilitary operation areas (MOA) consist of airspaceof defined vertical and lateral limits established forthe purpose of separating certain military trainingactivity from IFR traffic. There is no restrictionagainst a pilot operating VFR in these areas; how-ever, a pilot should be alert since training activitiesmay include acrobatic and abrupt maneuvers. MOAsare depicted on aeronautical charts.

ALERT AREASAlert areas are depicted on aeronautical charts and areto advise pilots that a high volume of pilot training orunusual aerial activity is taking place.

CONTROLLED FIRING AREASControlled firing areas contain activities, which, ifnot conducted in a controlled environment, could behazardous to nonparticipating aircraft. The differencebetween controlled firing areas and other special useairspace is that activities must be suspended when aspotter aircraft, radar, or ground lookout positionindicates an aircraft might be approaching the area.

OTHER AIRSPACE AREAS“Other airspace areas” is a general term referring tothe majority of the remaining airspace. It includes:

• Airport Advisory Areas

• Military Training Routes (MTR)

• Temporary Flight Restrictions

• Parachute Jump Areas

• Published VFR Routes

• Terminal Radar Service Areas

• National Security Areas

AIRPORT ADVISORY AREASAn airport advisory area is an area within 10 statutemiles (SM) of an airport where a control tower is notoperating, but where a flight service station (FSS) islocated. At these locations, the FSS provides advi-sory service to arriving and departing aircraft.

MILITARY TRAINING ROUTESMilitary training routes (MTR) are developed toallow the military to conduct low-altitude, high-speed training. The routes above 1,500 feet AGLare developed to be flown primarily under IFR, andthe routes 1,500 feet and less are for VFR flight.The routes are identified on sectional charts by thedesignation “instrument (IR) or visual (VR).”

TEMPORARY FLIGHT RESTRICTIONSAn FDC NOTAM will be issued to designate a tem-porary flight restriction (TFR). The NOTAM willbegin with the phrase “FLIGHT RESTRICTIONS”followed by the location of the temporary restriction,effective time period, area defined in statute miles,and altitudes affected. The NOTAM will also containthe FAA coordination facility and telephone number,the reason for the restriction, and any other informa-tion deemed appropriate. The pilot should check theNOTAMs as part of flight planning.

Some of the purposes for establishing a temporaryrestriction are:

• Protect persons and property in the air or on the surface from an existing or imminent hazard.

• Provide a safe environment for the operation of disaster relief aircraft.

• Prevent an unsafe congestion of sightseeingaircraft above an incident or event, which maygenerate a high degree of public interest.

• Protect declared national disasters for humanitarian reasons in the State of Hawaii.

• Protect the President, Vice President, or other public figures.

• Provide a safe environment for space agency operations.

PARACHUTE JUMP AREASParachute jump areas are published in theAirport/Facility Directory. Sites that are used fre-quently are depicted on sectional charts.

PUBLISHED VFR ROUTESPublished VFR routes are for transitioning around,under, or through some complex airspace. Termssuch as VFR flyway, VFR corridor, Class B airspace,VFR transition route, and terminal area VFR routehave been applied to such routes. These routes aregenerally found on VFR terminal area planningcharts.

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TERMINAL RADAR SERVICE AREASTerminal Radar Service Areas (TRSA) are areaswhere participating pilots can receive additional radarservices. The purpose of the service is to provide sep-aration between all IFR operations and participatingVFR aircraft.

The primary airport(s) within the TRSA become(s)Class D airspace. The remaining portion of the TRSAoverlies other controlled airspace, which is normallyClass E airspace beginning at 700 or 1,200 feet andestablished to transition to/from the en route terminalenvironment. TRSAs are depicted on VFR sectionalcharts and terminal area charts with a solid black line

and altitudes for each segment. The Class D portion ischarted with a blue segmented line.

Participation in TRSA services is voluntary; however,pilots operating under VFR are encouraged to contactthe radar approach control and take advantage ofTRSA service.

NATIONAL SECURITY AREASNational security areas consist of airspace ofdefined vertical and lateral dimensions establishedat locations where there is a requirement forincreased security and safety of ground facilities.Pilots are requested to voluntarily avoid flyingthrough these depicted areas. When necessary, flightmay be temporarily prohibited.

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This chapter provides an introduction to cross-country flying under visual flight rules (VFR). It contains practical information for planning and executing cross-country flights for the beginningpilot.

Air navigation is the process of piloting an airplanefrom one geographic position to another while monitor-ing one’s position as the flight progresses. It introducesthe need for planning, which includes plotting thecourse on an aeronautical chart, selecting checkpoints,measuring distances, obtaining pertinent weather infor-mation, and computing flight time, headings, and fuelrequirements. The methods used in this chapter includepilotage—navigating by reference to visible landmarks,dead reckoning—computations of direction and dis-tance from a known position, and radio navigation—byuse of radio aids.

AERONAUTICAL CHARTSAn aeronautical chart is the road map for a pilot flyingunder VFR. The chart provides information whichallows pilots to track their position and provides avail-able information which enhances safety. The threeaeronautical charts used by VFR pilots are:

• Sectional Charts

• VFR Terminal Area Charts

• World Aeronautical Charts

A free catalog listing aeronautical charts and relatedpublications including prices and instructions for

ordering is available at the National AeronauticalCharting Office (NACO) Web site: www.naco.faa.gov.

SECTIONAL CHARTSSectional charts are the most common charts usedby pilots today. The charts have a scale of 1:500,000(1 inch = 6.86 nautical miles or approximately 8statute miles) which allows for more detailed infor-mation to be included on the chart.

The charts provide an abundance of information,including airport data, navigational aids, airspace,and topography. Figure 14-1 on the next page is anexcerpt from the legend of a sectional chart. Byreferring to the chart legend, a pilot can interpretmost of the information on the chart. A pilot shouldalso check the chart for other legend information,which includes air traffic control frequencies andinformation on airspace. These charts are revisedsemiannually except for some areas outside theconterminous United States where they are revisedannually.

VISUAL FLIGHT RULETERMINAL AREA CHARTSVisual flight rule (VFR) terminal area charts are help-ful when flying in or near Class B airspace. Theyhave a scale of 1:250,000 (1 inch = 3.43 nauticalmiles or approximately 4 statute miles). These chartsprovide a more detailed display of topographicalinformation and are revised semiannually, except forseveral Alaskan and Caribbean charts.

WORLD AERONAUTICAL CHARTSWorld aeronautical charts are designed to provide astandard series of aeronautical charts, covering land

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areas of the world, at a size and scale convenient fornavigation by moderate speed aircraft. They are pro-duced at a scale of 1:1,000,000 (1 inch = 13.7 nauticalmiles or approximately 16 statute miles). These chartsare similar to sectional charts and the symbols are thesame except there is less detail due to the smaller scale.These charts are revised annually except severalAlaskan charts and the Mexican/Caribbean chartswhich are revised every 2 years.

LATITUDE AND LONGITUDE(MERIDIANS AND PARALLELS)The Equator is an imaginary circle equidistant from thepoles of the Earth. Circles parallel to the Equator (linesrunning east and west) are parallels of latitude. Theyare used to measure degrees of latitude north or southof the Equator. The angular distance from the Equator

to the pole is one-fourth of a circle or 90°. The 48 con-terminous states of the United States are locatedbetween 25° and 49° N. latitude. The arrows in figure14-2 labeled “LATITUDE” point to lines of latitude.

Meridians of longitude are drawn from the North Poleto the South Pole and are at right angles to the Equator.The “Prime Meridian” which passes throughGreenwich, England, is used as the zero line fromwhich measurements are made in degrees east and westto 180°. The 48 conterminous states of the UnitedStates are between 67° and 125° W. Longitude. Thearrows in figure 14-2 labeled “LONGITUDE” point tolines of longitude.

Any specific geographical point can thus be located byreference to its longitude and latitude. Washington, DCfor example, is approximately 39° N. latitude, 77° W.longitude. Chicago is approximately 42° N. latitude,88° W. longitude.

TIME ZONESThe meridians are also useful for designating timezones. A day is defined as the time required for theEarth to make one complete rotation of 360°. Since theday is divided into 24 hours, the Earth revolves at therate of 15° an hour. Noon is the time when the Sun isdirectly above a meridian; to the west of that meridianis morning, to the east is afternoon.

The standard practice is to establish a time zone foreach 15° of longitude. This makes a difference ofexactly 1 hour between each zone. In the United States,there are four time zones. The time zones are Eastern(75°), Central (90°), Mountain (105°), and Pacific(120°). The dividing lines are somewhat irregularFigure 14-1. Sectional chart legend.

E Q U A T O R

Longitude

Latit

ude

135°W120°

W 105°W

90°W

75°W

60°W

45°W

15°W

15°E

30°W

PR

IME

ME

RID

IAN

90°N

75°N

60°N

45°N

15°N

15°S

30°S

30°N

Figure 14-2. Meridians and parallels—the basis of measuringtime, distance, and direction.

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because communities near the boundaries often find itmore convenient to use time designations of neighbor-ing communities or trade centers.

Figure 14-3 shows the time zones in the United States.When the Sun is directly above the 90th meridian, it isnoon Central Standard Time. At the same time, it willbe 1 p.m. Eastern Standard Time, 11 a.m. MountainStandard Time, and 10 a.m. Pacific Standard Time.When “daylight saving” time is in effect, generallybetween the last Sunday in April and the last Sunday inOctober, the Sun is directly above the 75th meridian atnoon, Central Daylight Time.

These time zone differences must be taken into accountduring long flights eastward—especially if the flightmust be completed before dark. Remember, an hour islost when flying eastward from one time zone toanother, or perhaps even when flying from the westernedge to the eastern edge of the same time zone.Determine the time of sunset at the destination by con-sulting the flight service stations (AFSS/FSS) orNational Weather Service (NWS) and take this intoaccount when planning an eastbound flight.

In most aviation operations, time is expressed in termsof the 24-hour clock. Air traffic control instructions,weather reports and broadcasts, and estimated times ofarrival are all based on this system. For example: 9 a.m.is expressed as 0900, 1 p.m. is 1300, and 10 p.m. is2200.

Because a pilot may cross several time zones during aflight, a standard time system has been adopted. It iscalled Universal Coordinated Time (UTC) and is oftenreferred to as Zulu time. UTC is the time at the 0° lineof longitude which passes through Greenwich,

England. All of the time zones around the world arebased on this reference. To convert to this time, a pilotshould do the following:

Eastern Standard Time..........Add 5 hours

Central Standard Time..........Add 6 hours

Mountain Standard Time...... Add 7 hours

Pacific Standard Time.......... Add 8 hours

For daylight saving time, 1 hour should be subtractedfrom the calculated times.

MEASUREMENT OF DIRECTIONBy using the meridians, direction from one point toanother can be measured in degrees, in a clockwisedirection from true north. To indicate a course to be fol-lowed in flight, draw a line on the chart from the pointof departure to the destination and measure the anglewhich this line forms with a meridian. Direction isexpressed in degrees, as shown by the compass rose infigure 14-4.

Because meridians converge toward the poles, coursemeasurement should be taken at a meridian near themidpoint of the course rather than at the point of depar-ture. The course measured on the chart is known as thetrue course. This is the direction measured by referenceto a meridian or true north. It is the direction ofintended flight as measured in degrees clockwise fromtrue north.

11:00 AM 12: NOON 1:00 PM10:00 AM

120°

105°

90°

75°Pacific StandardTime Meridian

Mountain StandardTime Meridian

Central StandardTime Meridian

Eastern StandardTime Meridian

Figure 14-3.Time zones.

360

180

90270

10 2030

40

50

60

70

80

100

110

120

130

140150

160170190200210

220

230

240

250

260

280

290

300

310320

330340

350

N

S

NW

SE

NE

SW

EW

SS

E

ESE

ENE

NN

E

NN

W

WNW

WSW

SS

W

Figure 14-4. Compass rose.

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As shown in figure 14-5, the direction from A to Bwould be a true course of 065°, whereas the return trip(called the reciprocal) would be a true course of 245°.

The true heading is the direction in which the nose ofthe airplane points during a flight when measured indegrees clockwise from true north. Usually, it is neces-sary to head the airplane in a direction slightly differentfrom the true course to offset the effect of wind.Consequently, numerical value of the true heading maynot correspond with that of the true course. This will bediscussed more fully in subsequent sections in thischapter. For the purpose of this discussion, assume ano-wind condition exists under which heading andcourse would coincide. Thus, for a true course of 065°,the true heading would be 065°. To use the compassaccurately, however, corrections must be made formagnetic variation and compass deviation.

VARIATIONVariation is the angle between true north and magneticnorth. It is expressed as east variation or west variationdepending upon whether magnetic north (MN) is to theeast or west of true north (TN).

The north magnetic pole is located close to 71° N. lati-tude, 96° W. longitude and is about 1,300 miles fromthe geographic or true north pole, as indicated in figure14-6. If the Earth were uniformly magnetized, the com-pass needle would point toward the magnetic pole, inwhich case the variation between true north (as shownby the geographical meridians) and magnetic north (asshown by the magnetic meridians) could be measuredat any intersection of the meridians.

Actually, the Earth is not uniformly magnetized. In theUnited States, the needle usually points in the generaldirection of the magnetic pole, but it may vary in certaingeographical localities by many degrees. Consequently,the exact amount of variation at thousands of selectedlocations in the United States has been carefully deter-mined. The amount and the direction of variation, whichchange slightly from time to time, are shown on mostaeronautical charts as broken magenta lines, called iso-gonic lines, which connect points of equal magnetic

variation. (The line connecting points at which there isno variation between true north and magnetic north isthe agonic line.) An isogonic chart is shown in figure14-6. Minor bends and turns in the isogonic and agoniclines are caused by unusual geological conditionsaffecting magnetic forces in these areas.

On the west coast of the United States, the compassneedle points to the east of true north; on the east coast,the compass needle points to the west of true north.Zero degree variation exists on the agonic line, wheremagnetic north and true north coincide. This line runsroughly west of the Great Lakes, south throughWisconsin, Illinois, western Tennessee, and along theborder of Mississippi and Alabama. [Compare figures14-7 and 14-8.]

Because courses are measured in reference to geograph-ical meridians which point toward true north, and thesecourses are maintained by reference to the compasswhich points along a magnetic meridian in the generaldirection of magnetic north, the true direction must beconverted into magnetic direction for the purpose offlight. This conversion is made by adding or subtractingthe variation which is indicated by the nearest isogonicline on the chart. The true heading, when corrected forvariation, is known as magnetic heading.

If the variation is shown as “9°E,” this means that mag-netic north is 9° east of true north. If a true heading of360° is to be flown, 9° must be subtracted from 360°,which results in a magnetic heading of 351°. To fly

A x

x BCourse A to B 065°

Course B to A 245°

065°

245°

Figure 14-5. Courses are determined by reference to meridi-ans on aeronautical charts.

TN

MN

Figure 14-6. Isogonic chart. Magnetic meridians are in black;geographic meridians and parallels are in blue. Variation isthe angle between a magnetic and geographic meridian.

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east, a magnetic heading of 081° (090° – 9°) would beflown. To fly south, the magnetic heading would be171° (180° – 9°). To fly west, it would be 261° (270° –9°). To fly a true heading of 060°, a magnetic headingof 051° (060° – 9°) would be flown.

Remember, to convert true course or heading to mag-netic course or heading, note the variation shown bythe nearest isogonic line. If variation is west, add; ifeast, subtract. One method for remembering whether toadd or subtract variation is the phrase “east is least(subtract) and west is best (add).”

DEVIATIONDetermining the magnetic heading is an intermediatestep necessary to obtain the correct compass headingfor the flight. To determine compass heading, a correc-tion for deviation must be made. Because of magneticinfluences within the airplane such as electrical cir-cuits, radio, lights, tools, engine, and magnetized metalparts, the compass needle is frequently deflected fromits normal reading. This deflection is deviation. Thedeviation is different for each airplane, and it also mayvary for different headings in the same airplane. For

instance, if magnetism in the engine attracts the northend of the compass, there would be no effect when theplane is on a heading of magnetic north. On easterly orwesterly headings, however, the compass indicationswould be in error, as shown in figure 14-9. Magneticattraction can come from many other parts of the air-plane; the assumption of attraction in the engine ismerely used for the purpose of illustration.

Some adjustment of the compass, referred to as com-pensation, can be made to reduce this error, but theremaining correction must be applied by the pilot.

Proper compensation of the compass is best performedby a competent technician. Since the magnetic forceswithin the airplane change, because of landing shocks,vibration, mechanical work, or changes in equipment,the pilot should occasionally have the deviation of thecompass checked. The procedure used to check thedeviation (called “swinging the compass”) is brieflyoutlined.

The airplane is placed on a magnetic compass rose, theengine started, and electrical devices normally used(such as radio) are turned on. Tailwheel-type airplanesshould be jacked up into flying position. The airplane isaligned with magnetic north indicated on the compass

EASTERLY VARIATION WESTERLY VARIATION0°

0°5°

5°5°

5°

10°

10°10°

10°

15°

15°15°

15°

20°

20°20°

20°

Agonic Line

Figure 14-7. A typical isogonic chart. The black lines are iso-gonic lines which connect geographic points with identicalmagnetic variation.

West

VariationVariation

East

ZeroVariation

NP

MP

SPSP SP

MPMP

NPNP

Compass needle pointing east of true north Compass needle pointing to truenorth (along agonic line)

Compass needle pointing west of true north

Figure 14-8. Effect of variation on the compass.

Magnetic North Magnetic North

Magnetic North

CompassDeflectionDeviation

CompassDeflectionDeviation

MagnetizedEngine Magnetized

EngineCompass

No Deviation

Figure 14-9. Magnetized portions of the airplane cause thecompass to deviate from its normal indications.

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rose and the reading shown on the compass is recordedon a deviation card. The airplane is then aligned at 30°intervals and each reading is recorded. If the airplane isto be flown at night, the lights are turned on and anysignificant changes in the readings are noted. If so,additional entries are made for use at night.

The accuracy of the compass can also be checked bycomparing the compass reading with the known run-way headings.

A deviation card, similar to figure 14-10, is mountednear the compass, showing the addition or subtractionrequired to correct for deviation on various headings,usually at intervals of 30°. For intermediate readings,the pilot should be able to interpolate mentally withsufficient accuracy. For example, if the pilot needed thecorrection for 195° and noted the correction for 180° tobe 0° and for 210° to be +2°, it could be assumed thatthe correction for 195° would be +1°. The magneticheading, when corrected for deviation, is known ascompass heading.

The following method is used by many pilots to deter-mine compass heading: After the true course (TC) ismeasured, and wind correction applied resulting in a trueheading (TH), the sequence TH ± variation (V) = MH ±deviation (D) = compass heading (CH) is followed toarrive at compass heading. [Figure 14-11]

EFFECT OF WINDThe preceding discussion explained how to measure atrue course on the aeronautical chart and how to makecorrections for variation and deviation, but oneimportant factor has not been considered—wind. Asdiscussed in the study of the atmosphere, wind is amass of air moving over the surface of the Earth in adefinite direction. When the wind is blowing from thenorth at 25 knots, it simply means that air is movingsouthward over the Earth’s surface at the rate of 25nautical miles (NM) in 1 hour.

Under these conditions, any inert object free from con-tact with the Earth will be carried 25 NM southward in1 hour. This effect becomes apparent when such thingsas clouds, dust, and toy balloons are observed beingblown along by the wind. Obviously, an airplane flyingwithin the moving mass of air will be similarlyaffected. Even though the airplane does not float freely

with the wind, it moves through the air at the same timethe air is moving over the ground, thus is affected bywind. Consequently, at the end of 1 hour of flight, theairplane will be in a position which results from a com-bination of these two motions:

• the movement of the air mass in reference to theground, and

• the forward movement of the airplane through theair mass.

Actually, these two motions are independent. So far asthe airplane’s flight through the air is concerned, itmakes no difference whether the mass of air throughwhich the airplane is flying is moving or is stationary.A pilot flying in a 70-knot gale would be totallyunaware of any wind (except for possible turbulence)unless the ground were observed. In reference to theground, however, the airplane would appear to flyfaster with a tailwind or slower with a headwind, or todrift right or left with a crosswind.

As shown in figure 14-12, an airplane flying eastwardat an airspeed of 120 knots in still air, will have agroundspeed exactly the same—120 knots. If the massof air is moving eastward at 20 knots, the airspeed ofthe airplane will not be affected, but the progress of theairplane over the ground will be 120 plus 20, or agroundspeed of 140 knots. On the other hand, if themass of air is moving westward at 20 knots, the air-speed of the airplane still remains the same, butgroundspeed becomes 120 minus 20 or 100 knots.

Figure 14-10. Compass deviation card.

Figure 14-11. Relationship between true, magnetic, and com-pass headings for a particular instance.

FOR (MAGNETIC)..........STEER (COMPASS).......

FOR (MAGNETIC)..........STEER (COMPASS).......

N0S

180

3028

210212

6057

240243

E86W

274

120117300303

150148330332

TN MN CN

VAR

10° E DE

V 4

CH-074°MH-078°TH-088°

Heading

TN MN CN

DE

V 4

°

CH-074°MH-078°TH-088°

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Assuming no correction is made for wind effect, if theairplane is heading eastward at 120 knots, and the airmass moving southward at 20 knots, the airplane atthe end of 1 hour will be almost 120 miles east of itspoint of departure because of its progress through theair. It will be 20 miles south because of the motion ofthe air. Under these circumstances, the airspeedremains 120 knots, but the groundspeed is determinedby combining the movement of the airplane with thatof the air mass. Groundspeed can be measured as thedistance from the point of departure to the position ofthe airplane at the end of 1 hour. The groundspeed canbe computed by the time required to fly between twopoints a known distance apart. It also can be deter-mined before flight by constructing a wind triangle,which will be explained later in this chapter. [Figure14-13]

The direction in which the plane is pointing as it flies isheading. Its actual path over the ground, which is acombination of the motion of the airplane and themotion of the air, is track. The angle between the head-ing and the track is drift angle. If the airplane’s headingcoincides with the true course and the wind is blowingfrom the left, the track will not coincide with the truecourse. The wind will drift the airplane to the right, sothe track will fall to the right of the desired course ortrue course. [Figure 14-14]

By determining the amount of drift, the pilot cancounteract the effect of the wind and make the trackof the airplane coincide with the desired course. If themass of air is moving across the course from the left,the airplane will drift to the right, and a correctionmust be made by heading the airplane sufficiently tothe left to offset this drift. To state in another way, ifthe wind is from the left, the correction will be madeby pointing the airplane to the left a certain number ofdegrees, therefore correcting for wind drift. This iswind correction angle and is expressed in terms ofdegrees right or left of the true course. [Figure 14-15]

To summarize:

• COURSE—is the intended path of an airplaneover the ground; or the direction of a line drawnon a chart representing the intended airplane path,expressed as the angle measured from a specificreference datum clockwise from 0° through 360°to the line.

GROUNDSPEED 120 KTS

GROUNDSPEED 100 KTS

AIRSPEED120 KTS

AIR NOT MOVING

GROUNDSPEED 140 KTS

AIR MOVING 20 KNOTSAIRSPEED120 KTS

AIRSPEED120 KTS

AIR MOVING 20 KNOTS

Figure 14-12. Motion of the air affects the speed with whichairplanes move over the Earth’s surface. Airspeed, the rate atwhich an airplane moves through the air, is not affected by airmotion.

Distance Covered Over Ground (1 Hour)

Airspeed Effect (1 Hour)

20 Knots

Figure 14-13. Airplane flightpath resulting from its airspeedand direction, and the windspeed and direction.

Heading

TrackDesiredCourse

Wind

Drift Angle

Figure 14-14. Effects of wind drift on maintaining desiredcourse.

Heading

Track DesiredCourse

Wind

Wind Correction Angle

Figure 14-15. Establishing a wind correction angle that willcounteract wind drift and maintain the desired course.

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• HEADING—is the direction in which the noseof the airplane points during flight.

• TRACK—is the actual path made over theground in flight. (If proper correction has beenmade for the wind, track and course will be iden-tical.)

• DRIFT ANGLE—is the angle between headingand track.

• WIND CORRECTION ANGLE—is correctionapplied to the course to establish a heading so thattrack will coincide with course.

• AIRSPEED—is the rate of the airplane’sprogress through the air.

• GROUNDSPEED—is the rate of the airplane’sin-flight progress over the ground.

BASIC CALCULATIONSBefore a cross-country flight, a pilot should make com-mon calculations for time, speed, and distance, and theamount of fuel required.

CONVERTING MINUTES TO EQUIVALENTHOURSIt frequently is necessary to convert minutes into equiv-alent hours when solving speed, time, and distanceproblems. To convert minutes to hours, divide by 60(60 minutes = 1 hour). Thus, 30 minutes 30/60 = 0.5hour. To convert hours to minutes, multiply by 60.Thus, 0.75 hour equals 0.75 x 60 = 45 minutes.

Time T = D/GSTo find the time (T) in flight, divide the distance (D)by the groundspeed (GS). The time to fly 210 nauticalmiles at a groundspeed of 140 knots is 210 divided by140, or 1.5 hours. (The 0.5 hour multiplied by 60 min-utes equals 30 minutes.) Answer: 1:30.

Distance D = GS X TTo find the distance flown in a given time, multiplygroundspeed by time. The distance flown in 1 hour 45minutes at a groundspeed of 120 knots is 120 x 1.75, or210 nautical miles.

Groundspeed GS = D/TTo find the groundspeed, divide the distance flown bythe time required. If an airplane flies 270 nautical milesin 3 hours, the groundspeed is 270 divided by 3 = 90knots.

CONVERTING KNOTS TO MILES PER HOURAnother conversion is that of changing knots to milesper hour. The aviation industry is using knots morefrequently than miles per hour, but it might be well to

discuss the conversion for those who do use miles perhour when working with speed problems. TheNational Weather Service reports both surface windsand winds aloft in knots. However, airspeed indica-tors in some airplanes are calibrated in miles per hour(although many are now calibrated in both miles perhour and knots). Pilots, therefore, should learn toconvert windspeeds in knots to miles per hour.

A knot is 1 nautical mile per hour. Because there are6,076.1 feet in a nautical mile and 5,280 feet in a statutemile, the conversion factor is 1.15. To convert knots tomiles per hour, multiply knots by 1.15. For example: awindspeed of 20 knots is equivalent to 23 miles perhour.

Most flight computers or electronic calculators have ameans of making this conversion. Another quickmethod of conversion is to use the scales of nauticalmiles and statute miles at the bottom of aeronauticalcharts.

FUEL CONSUMPTIONAirplane fuel consumption is computed in gallons perhour. Consequently, to determine the fuel required for agiven flight, the time required for the flight must beknown. Time in flight multiplied by rate of consump-tion gives the quantity of fuel required. For example, aflight of 400 NM at a groundspeed of 100 knotsrequires 4 hours. If the plane consumes 5 gallons anhour, the total consumption will be 4 x 5, or 20 gallons.

The rate of fuel consumption depends on many factors:condition of the engine, propeller pitch, propellerr.p.m., richness of the mixture, and particularly the per-centage of horsepower used for flight at cruising speed.The pilot should know the approximate consumptionrate from cruise performance charts, or from experi-ence. In addition to the amount of fuel required for theflight, there should be sufficient fuel for reserve.

FLIGHT COMPUTERSUp to this point, only mathematical formulas have beenused to determine such items as time, distance, speed,and fuel consumption. In reality, most pilots will use amechanical or electronic flight computer. These devicescan compute numerous problems associated with flightplanning and navigation. The mechanical or electroniccomputer will have an instruction book and most likelysample problems so the pilot can become familiar withits functions and operation. [Figure 14-16]

PLOTTERAnother aid in flight planning is a plotter, which is aprotractor and ruler. The pilot can use this whendetermining true course and measuring distance.Most plotters have a ruler which measures in both

14-8

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7 8 9

4 5 6

1 2 3

0

:

x

-

+

=

CMP

ClrOn/OffMode

Dist

Sto

Vol Wt Wx

+/-

TSD Alt: As Wind Wt. Bal Timer Conv: Dist Vol Wt Wx

INSTRUCTIONS FOR USE

1. Place hole over intersection of true course and true north line.2. Without changing position rotate plotter until edge is over true course line.3. From hole follow true north line to curved scale with arrow pointing in direction of flight.4. Read true course in degrees, on proper scale, over true north line. read scales counter-clockwise.

SECTIONAL CHART SIDE - 1:500,000 NAVIGATIONAL FLIGHT PLOTTER

0

180

270

90

10

190 280

100

20

200 290

110

30

210

330

150 340

160

350

170 300

120

310 130

320

140

330

150

340 16

0

350 17

0 190

10

200

20

210

30

220

40

230

50 240

60 250

70

260

80

NAUTICAL 5 MILES 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 NAUTICAL 85 MILES

0 STATUTE 5 MILES 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 9585 100 90

DEGREES

Figure 14-16. A picture of the computational and wind side of a common mechanical computer, an electronic computer, and plotter.

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nautical and statute miles and has a scale for a sec-tional chart on one side and a world aeronautical charton the other. [Figure 14-16]

PILOTAGEPilotage is navigation by reference to landmarks orcheckpoints. It is a method of navigation that can beused on any course that has adequate checkpoints, butit is more commonly used in conjunction with deadreckoning and VFR radio navigation.

The checkpoints selected should be prominent featurescommon to the area of the flight. Choose checkpointsthat can be readily identified by other features such asroads, rivers, railroad tracks, lakes, and power lines. Ifpossible, select features that will make useful bound-aries or brackets on each side of the course, such ashighways, rivers, railroads, and mountains. A pilot cankeep from drifting too far off course by referring to andnot crossing the selected brackets. Never place com-plete reliance on any single checkpoint. Choose amplecheckpoints. If one is missed, look for the next onewhile maintaining the heading. When determiningposition from checkpoints, remember that the scale of asectional chart is 1 inch = 8 statute miles or 6.86 nauti-cal miles. For example, if a checkpoint selected wasapproximately one-half inch from the course line onthe chart, it is 4 statue miles or 3.43 nautical miles fromthe course on the ground. In the more congested areas,some of the smaller features are not included on thechart. If confused, hold the heading. If a turn is madeaway from the heading, it will be easy to become lost.

Roads shown on the chart are primarily the well-trav-eled roads or those most apparent when viewed fromthe air. New roads and structures are constantly beingbuilt, and may not be shown on the chart until the nextchart is issued. Some structures, such as antennas maybe difficult to see. Sometimes TV antennas are groupedtogether in an area near a town. They are supported byalmost invisible guy wires. Never approach an area ofantennas less than 500 feet above the tallest one. Mostof the taller structures are marked with strobe lights tomake them more visible to a pilot. However, someweather conditions or background lighting may makethem difficult to see. Aeronautical charts display thebest information available at the time of printing, but apilot should be cautious for new structures or changesthat have occurred since the chart was printed.

DEAD RECKONINGDead reckoning is navigation solely by means ofcomputations based on time, airspeed, distance, anddirection. The products derived from these variables,when adjusted by windspeed and velocity, are head-ing and groundspeed. The predicted heading willguide the airplane along the intended path and the

groundspeed will establish the time to arrive at eachcheckpoint and the destination. Except for flightsover water, dead reckoning is usually used withpilotage for cross-country flying. The heading andgroundspeed as calculated is constantly monitoredand corrected by pilotage as observed from check-points.

THE WIND TRIANGLE ORVECTOR ANALYSISIf there is no wind, the airplane’s ground track will bethe same as the heading and the groundspeed will bethe same as the true airspeed. This condition rarelyexists. A wind triangle, the pilot’s version of vectoranalysis, is the basis of dead reckoning.

The wind triangle is a graphic explanation of theeffect of wind upon flight. Groundspeed, heading, andtime for any flight can be determined by using thewind triangle. It can be applied to the simplest kind ofcross-country flight as well as the most complicatedinstrument flight. The experienced pilot becomes sofamiliar with the fundamental principles that esti-mates can be made which are adequate for visualflight without actually drawing the diagrams. Thebeginning student, however, needs to develop skill inconstructing these diagrams as an aid to the completeunderstanding of wind effect. Either consciously orunconsciously, every good pilot thinks of the flight interms of wind triangle.

If a flight is to be made on a course to the east, with awind blowing from northeast, the airplane must beheaded somewhat to the north of east to counteractdrift. This can be represented by a diagram as shown infigure 14-17. Each line represents direction and speed.The long dotted line shows the direction the plane isheading, and its length represents the airspeed for 1hour. The short dotted line at the right shows the winddirection, and its length represents the wind velocity

N

S

WindDirection

andVelocity

Heading and Airspeed

Course and Groundspeed

Figure 14-17. Principle of the wind triangle.

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for 1 hour. The solid line shows the direction of thetrack, or the path of the airplane as measured over theEarth, and its length represents the distance traveled in1 hour, or the groundspeed.

In actual practice, the triangle illustrated in figure 14-17is not drawn; instead, construct a similar triangle asshown by the black lines in figure 14-18, which isexplained in the following example.

Suppose a flight is to be flown from E to P. Draw a lineon the aeronautical chart connecting these two points;measure its direction with a protractor, or plotter, in ref-erence to a meridian. This is the true course, which inthis example is assumed to be 090° (east). From theNational Weather Service, it is learned that the wind atthe altitude of the intended flight is 40 knots from thenortheast (045°). Since the National Weather Servicereports the windspeed in knots, if the true airspeed ofthe airplane is 120 knots, there is no need to convertspeeds from knots to miles per hour or vice versa.

Now on a plain sheet of paper draw a vertical line rep-resenting north and south. (The various steps are shownin figure 14-19.)

Place the protractor with the base resting on the verti-cal line and the curved edge facing east. At the centerpoint of the base, make a dot labeled “E” (point ofdeparture), and at the curved edge, make a dot at 90°(indicating the direction of the true course) and anotherat 45° (indicating wind direction).

With the ruler, draw the true course line from E,extending it somewhat beyond the dot by 90°, andlabeling it “TC 090°.”

Next, align the ruler with E and the dot at 45°, and drawthe wind arrow from E, not toward 045°, but downwindin the direction the wind is blowing, making it 40 unitslong, to correspond with the wind velocity of 40 knots.Identify this line as the wind line by placing the letter“W” at the end to show the wind direction. Finally,measure 120 units on the ruler to represent the airspeed,making a dot on the ruler at this point. The units usedmay be of any convenient scale or value (such as 1/4 inch= 10 knots), but once selected, the same scale must beused for each of the linear movements involved. Thenplace the ruler so that the end is on the arrowhead (W)and the 120-knot dot intercepts the true course line.Draw the line and label it “AS 120.” The point “P”placed at the intersection represents the position of theairplane at the end of 1 hour. The diagram is now com-plete.

The distance flown in 1 hour (groundspeed) is meas-ured as the numbers of units on the true course line (88nautical miles per hour or 88 knots).

The true heading necessary to offset drift is indicatedby the direction of the airspeed line, which can bedetermined in one of two ways:

• By placing the straight side of the protractoralong the north-south line, with its center point at

WindDirection

and Velocity

Heading and Airspeed

N

S

E

P

W

Courseand Groundspeed

Figure 14-18. The wind triangle as is drawn in navigationpractice. Dashed lines show the triangle as drawn in figure14-17.

N

S

N

S

N

S

E

E

W

W

TC 090°

TC 090° GS 88

Step 2 and 3Wind

90°

45°

Step 1

Step 4

MidPoint

AS 120

P

Figure 14-19. Steps in drawing the wind triangle.

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the intersection of the airspeed line and north-south line, read the true heading directly indegrees (076°). [Figure 14-20]

• By placing the straight side of the protractoralong the true course line, with its center at P, readthe angle between the true course and the airspeedline. This is the wind correction angle (WCA)which must be applied to the true course to obtainthe true heading. If the wind blows from the rightof true course, the angle will be added; if from theleft, it will be subtracted. In the example given,the WCA is 14° and the wind is from the left;therefore, subtract 14° from true course of 090°,making the true heading 076°. [Figure 14-21]

After obtaining the true heading, apply the correctionfor magnetic variation to obtain magnetic heading, andthe correction for compass deviation to obtain a com-pass heading. The compass heading can be used to flyto the destination by dead reckoning.

To determine the time and fuel required for the flight,first find the distance to destination by measuring thelength of the course line drawn on the aeronauticalchart (using the appropriate scale at the bottom of the

chart). If the distance measures 220 NM, divide by thegroundspeed of 88 knots, which gives 2.5 hours or(2:30), as the time required. If fuel consumption is 8gallons an hour, 8 x 2.5 or about 20 gallons will beused. Briefly summarized, the steps in obtaining flightinformation are as follows:

• TRUE COURSE—Direction of the line con-necting two desired points, drawn on the chartand measured clockwise in degrees from truenorth on the mid-meridian.

• WIND CORRECTION ANGLE—Determinedfrom the wind triangle. (Added to TC if the windis from the right; subtract if wind is from the left.)

• TRUE HEADING—The direction measured indegrees clockwise from true north, in which thenose of the plane should point to make good thedesired course.

• VARIATION—Obtained from the isogonic lineon the chart. (Added to TH if west; subtract ifeast.)

• MAGNETIC HEADING—An intermediatestep in the conversion. (Obtained by applyingvariation to true heading.)

• DEVIATION—Obtained from the deviationcard on the airplane. (Added to MH or subtractedfrom, as indicated.)

• COMPASS HEADING—The reading on thecompass (found by applying deviation to MH)which will be followed to make good the desiredcourse.

• TOTAL DISTANCE—Obtained by measuringthe length of the TC line on the chart (using thescale at the bottom of the chart).

• GROUNDSPEED—Obtained by measuring thelength of the TC line on the wind triangle (usingthe scale employed for drawing the diagram).

• ESTIMATED TIME EN ROUTE (ETE)—Total distance divided by groundspeed.

• FUEL RATE—Predetermined gallons per hourused at cruising speed.

NOTE: Additional fuel for adequate reserve should beadded as a safety measure.

N

S

E

W

TC 090° GS 88

TH 076° AS 120

WCA = 14° L

14°

P

Figure 14-21. Finding true heading by the wind correctionangle.

N

S

E

W

TC 090° GS 88

TH 076° AS 12076°

P

Figure 14-20. Finding true heading by direct measurement.

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FLIGHT PLANNINGTitle 14 of the Code of Federal Regulations (14 CFR)part 91 states, in part, that before beginning a flight, thepilot in command of an aircraft shall become familiarwith all available information concerning that flight.For flights not in the vicinity of an airport, this mustinclude information on available current weatherreports and forecasts, fuel requirements, alternativesavailable if the planned flight cannot be completed, andany known traffic delays of which the pilot incommand has been advised by air traffic control (ATC).

ASSEMBLING NECESSARY MATERIALThe pilot should collect the necessary material wellbefore the flight. An appropriate current sectional chartand charts for areas adjoining the flight route should beamong this material if the route of flight is near the bor-der of a chart.

Additional equipment should include a flight computeror electronic calculator, plotter, and any other itemappropriate to the particular flight—for example, if anight flight is to be undertaken, carry a flashlight; if aflight is over desert country, carry a supply of waterand other necessities.

WEATHER CHECKIt may be wise to check the weather before continuingwith other aspects of flight planning to see, first of all,if the flight is feasible and, if it is, which route is best.Chapter 11 on weather discusses obtaining a weatherbriefing.

USE OF THE AIRPORT/FACILITY DIRECTORYStudy available information about each airport atwhich a landing is intended. This should include astudy of the Notices to Airmen (NOTAMs) and theAirport/Facility Directory. [Figure 14-22] Thisincludes location, elevation, runway and lightingfacilities, available services, availability of aeronau-tical advisory station frequency (UNICOM), typesof fuel available (use to decide on refueling stops),AFSS/FSS located on the airport, control tower andground control frequencies, traffic information,remarks, and other pertinent information. TheNOTAMs, issued every 28 days, should be checkedfor additional information on hazardous conditionsor changes that have been made since issuance of theAirport/Facility Directory.

The sectional chart bulletin subsection should bechecked for major changes that have occurred since thelast publication date of each sectional chart being used.Remember, the chart may be up to 6 months old. Theeffective date of the chart appears at the top of the frontof the chart.

The Airport/Facility Directory will generally have thelatest information pertaining to such matters and shouldbe used in preference to the information on the back ofthe chart, if there are differences.

AIRPLANE FLIGHT MANUAL OR PILOT’SOPERATING HANDBOOKThe Airplane Flight Manual or Pilot’s OperatingHandbook (AFM/POH) should be checked to determinethe proper loading of the airplane (weight and balancedata). The weight of the usable fuel and drainable oilaboard must be known. Also, check the weight of thepassengers, the weight of all baggage to be carried, andthe empty weight of the airplane to be sure that the totalweight does not exceed the maximum allowable. Thedistribution of the load must be known to tell if theresulting center of gravity is within limits. Be sure touse the latest weight and balance information in theFAA-approved Airplane Flight Manual or other perma-nent airplane records, as appropriate, to obtain emptyweight and empty weight center-of-gravity information.

Determine the takeoff and landing distances from theappropriate charts, based on the calculated load, ele-vation of the airport, and temperature; then comparethese distances with the amount of runway available.Remember, the heavier the load and the higher the

Figure 14-22. Airport Facility Directory.

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elevation, temperature, or humidity, the longer thetakeoff roll and landing roll and the lower the rate ofclimb.

Check the fuel consumption charts to determine therate of fuel consumption at the estimated flight altitudeand power settings. Calculate the rate of fuel consump-tion, and then compare it with the estimated time forthe flight so that refueling points along the route can beincluded in the plan.

CHARTING THE COURSEOnce the weather has been checked and some prelimi-nary planning done, it is time to chart the course anddetermine the data needed to accomplish the flight. Thefollowing sections will provide a logical sequence tofollow in charting the course, filling out a flight log,and filing a flight plan. In the following example, a tripis planned based on the following data and the sectionalchart excerpt in figure 14-23.

Route of flight: Chickasha Airport direct to GuthrieAirport

True Airspeed (TAS)...............................115 knotsWinds Aloft.....................................360° at 10 knotsUsable fuel...........................................38 gallonsFuel Rate....................................................8 GPHDeviation.............................................................+2°

STEPS IN CHARTING THE COURSEThe following is a suggested sequence for arriving atthe pertinent information for the trip. As information isdetermined, it may be noted as illustrated in the exam-ple of a flight log in figure 14-24. Where calculationsare required, the pilot may use a mathematical formulaor a manual or electronic flight computer. If unfamiliarwith how to use a manual or electronic computer com-petently, it would be advantageous to read the opera-tion manual and work several practice problems at thispoint.

First draw a line from Chickasha Airport (point A)directly to Guthrie Airport (point F). The course lineshould begin at the center of the airport of departureand end at the center of the destination airport. If theroute is direct, the course line will consist of a singlestraight line. If the route is not direct, it will consist oftwo or more straight line segments—for example, aVOR station which is off the direct route, but whichwill make navigating easier, may be chosen (radio nav-igation is discussed later in this chapter).

Appropriate checkpoints should be selected along theroute and noted in some way. These should be easy-to-locate points such as large towns, large lakes and rivers,or combinations of recognizable points such as townswith an airport, towns with a network of highways, andrailroads entering and departing. Normally, chooseonly towns indicated by splashes of yellow on the

chart. Do not choose towns represented by a small cir-cle—these may turn out to be only a half-dozen houses.(In isolated areas, however, towns represented by asmall circle can be prominent checkpoints.) For thistrip, four checkpoints have been selected. Checkpoint 1consists of a tower located east of the course and can befurther identified by the highway and railroad track,which almost parallels the course at this point.Checkpoint 2 is the obstruction just to the west of thecourse and can be further identified by Will RogersAirport which is directly to the east. Checkpoint 3 isWiley Post Airport, which the airplane should flydirectly over. Checkpoint 4 is a private non-surfacedairport to the west of the course and can be further iden-tified by the railroad track and highway to the east ofthe course.

The course and areas on either side of the planned routeshould be checked to determine if there is any type ofairspace with which the pilot should be concerned orwhich has special operational requirements. For thistrip, it should be noted that the course will pass througha segment of the Class C airspace surrounding WillRogers Airport where the floor of the airspace is 2,500feet mean sea level (MSL) and the ceiling is 5,300 feetMSL (point B). Also, there is Class D airspace from thesurface to 3,800 feet MSL surrounding Wiley PostAirport (point C) during the time the control tower is inoperation.

Study the terrain and obstructions along the route.This is necessary to determine the highest and lowestelevations as well as the highest obstruction to beencountered so that an appropriate altitude which willconform to part 91 regulations can be selected. If theflight is to be flown at an altitude more than 3,000 feetabove the terrain, conformance to the cruising altitudeappropriate to the direction of flight is required.Check the route for particularly rugged terrain so itcan be avoided. Areas where a takeoff or landing willbe made should be carefully checked for tall obstruc-tions. TV transmitting towers may extend to altitudesover 1,500 feet above the surrounding terrain. It isessential that pilots be aware of their presence andlocation. For this trip, it should be noted that thetallest obstruction is part of a series of antennas with aheight of 2,749 feet MSL (point D). The highest ele-vation should be located in the northeast quadrant andis 2,900 feet MSL (point E).

Since the wind is no factor and it is desirable and withinthe airplane’s capability to fly above the Class C and Dairspace to be encountered, an altitude of 5,500 feetMSL will be chosen. This altitude also gives adequateclearance of all obstructions as well as conforms to thepart 91 requirement to fly at an altitude of odd thou-sand plus 500 feet when on a magnetic course between0 and 179°.

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Figure 14-23. Sectional chart excerpt.

A

F

1B

2

C3

D

E4

G

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Next, the pilot should measure the total distance of thecourse as well as the distance between checkpoints. Thetotal distance is 53 NM and the distance between check-points is as noted on the flight log in figure 14-24.

After determining the distance, the true course shouldbe measured. If using a plotter, follow the directions onthe plotter. The true course is 031°. Once the true head-ing is established, the pilot can determine the compassheading. This is done by following the formula givenearlier in this chapter. The formula is:

TC ± WCA = TH ± VAR = MH ± DEV = CH

The wind correction angle can be determined by usinga manual or electronic flight computer. Using a wind of360° at 10 knots, it is determined the WCA is 3° left.This is subtracted from the TC making the TH 28°.Next, the pilot should locate the isogonic line closest tothe route of the flight to determine variation. Point G infigure 14-23 shows the variation to be 6° 30�E(rounded to 7°E), which means it should be subtractedfrom the TH, giving an MH of 21°. Next, add 2° to theMH for the deviation correction. This gives the pilotthe compass heading which is 23°.

Next, the groundspeed should be determined. This canbe done using a manual or electronic calculator. It isdetermined the GS is 106 knots. Based on this infor-mation, the total trip time, as well as time betweencheckpoints, and the fuel burned can be determined.These calculations can be done mathematically or byusing a manual or electronic calculator.

For this trip, the GS is 106 knots and the total time is35 minutes (30 minutes plus 5 minutes for climb) witha fuel burn of 4.7 gallons. Refer to the flight log in fig-ure 14-24 for the time between checkpoints.

As the trip progresses, the pilot can note headings andtime and make adjustments in heading, groundspeed,and time.

FILING A VFR FLIGHT PLANFiling a flight plan is not required by regulations;however, it is a good operating practice, since theinformation contained in the flight plan can be used insearch and rescue in the event of an emergency.

Flight plans can be filed in the air by radio, but it is bestto file a flight plan either in person at the FSS or byphone just before departing. After takeoff, contact theFSS by radio and give them the takeoff time so theflight plan can be activated.

PILOT'S PLANNING SHEET

FUELRATE

TOTALFUELCOURSE TC WIND

KNOTS FROMWCAR+ L- TH VAR

W+ E- MH DEV CH TOTALMILES GS TOTAL

TIME

PLANE IDENTIFICATION N123DB DATE

From:To:From:To:

ChickashaGuthrie

031˚ 10 360˚ 3˚ L 28 7˚ E 21˚ +2˚ 23 53 106kts 35 min 8 GPH 38 gal

VISUAL FLIGHT LOG

NAVIGATIONAIDS

TIME OFDEPARTURE COURSE DISTANCE ELAPSED

TIME GS CH REMARKS

POINT OFDEPARTURE

NAVAIDIDENT.FREQ.

WEATHERAIRSPACE ETC.

CHECKPOINTS

DESTINATION

TOFROM

POINT

TO POINT

CUMULATIVE

ESTIMATED

ACTUALESTIM

ATED

ACTUAL

ESTIMATED

ACTUAL

#1

#2

#3

#4

Guthrie Airport

Chickasha Airport

11 NM

10NM

21 NM

10.5 NM

31.5 NM

13 NM

44.5 NM

8.5 NM

53 NM

6 MIN+5

6 MIN

6 MIN

7 MIN

5 MIN

106 kts

106 kts

106 kts

106 kts

023˚

023˚

023˚

023˚

Figure 14-24. Pilot’s planning sheet and visual flight log.

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When a VFR flight plan is filed, it will be held by theFSS until 1 hour after the proposed departure time andthen canceled unless: the actual departure time isreceived; or a revised proposed departure time isreceived; or at the time of filing, the FSS is informedthat the proposed departure time will be met, but actualtime cannot be given because of inadequate communi-cation. The FSS specialist who accepts the flight planwill not inform the pilot of this procedure, however.

Figure 14-25 shows the flight plan form a pilot fileswith the Flight Service Station. When filing a flightplan by telephone or radio, give the information in theorder of the numbered spaces. This enables the FSSspecialist to copy the information more efficiently.Most of the spaces are either self-explanatory or non-applicable to the VFR flight plan (such as item 13).However, some spaces may need explanation.

Item 3 asks for the airplane type and special equip-ment. An example would be C-150/X, which meansthe airplane has no transponder. A listing of specialequipment codes is listed in the AeronauticalInformation Manual (AIM).

Item 6 asks for the proposed departure time inUniversal Coordinated Time (indicated by the “Z”).

Item 7 asks for the cruising altitude. Normally,“VFR” can be entered in this block, since the pilotwill choose a cruising altitude to conform to FAAregulations.

Item 8 asks for the route of flight. If the flight is tobe direct, enter the word “direct;” if not, enter theactual route to be followed such as via certain townsor navigation aids.

Item 10 asks for the estimated time en route. In thesample flight plan, 5 minutes was added to the totaltime to allow for the climb.

Item 12 asks for the fuel on board in hours and min-utes. This is determined by dividing the total usablefuel aboard in gallons by the estimated rate of fuelconsumption in gallons.

Remember, there is every advantage in filing a flightplan; but do not forget to close the flight plan on arrival.Do this by telephone with the nearest FSS, if possible,to avoid radio congestion.

RADIO NAVIGATIONAdvances in navigational radio receivers installedin airplanes, the development of aeronauticalcharts which show the exact location of groundtransmitting stations and their frequencies, alongwith refined cockpit instrumentation make it pos-sible for pilots to navigate with precision toalmost any point desired. Although precision innavigation is obtainable through the proper use ofthis equipment, beginning pilots should use thisequipment to supplement navigation by visualreference to the ground (pilotage). This methodprovides the pilot with an effective safeguardagainst disorientation in the event of radio mal-function.

PROPOSED (Z) ACTUAL (Z)VFR

IFR

DVFR

TYPE1. AIRCRAFT TYPE/SPECIAL EQUIPMENT

3.AIRCRAFTIDENTIFICATION

2. TRUEAIRSPEED

4. DEPARTURE POINT5. CRUISINGALTITUDE

7.

ROUTE OF FLIGHT8.

DESTINATION (Name of airportand city)

9.

HOURS MINUTES

EST. TIME ENROUTE10. REMARKS11.

HOURS MINUTES

ALTERNATE AIRPORT(S)13.FUEL ON BOARD12. PILOT'S NAME, ADDRESS & TELEPHONE NUMBER & AIRCRAFT HOME BASE14. NUMBERABOARD

15.

COLOR OF AIRCRAFT16.___________________

DEPARTURE TIME6.

KTS

FLIGHT PLAN

X

N123DB C150/X 115CHICKASHA

AIRPORT 1400Z 5500

Chickasha direct Guthrie

Guthrie AirportGuthrie, OK

35

4 45

Jane SmithAero AirOklahoma City, OK (405) 555-4149

1

Red/White McAlesterCLOSE VFR FLIGHT PLAN WITH FSS ON ARRIVAL

Figure 14-25. Flight plan form.

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There are four radio navigation systems available foruse for VFR navigation. These are:

VHF Omnidirectional Range (VOR)

Nondirectional Radiobeacon (NDB)

Long Range Navigation (LORAN-C)

Global Positioning System (GPS)

VERY HIGH FREQUENCY (VHF)OMNIDIRECTIONAL RANGE (VOR)The VOR system is present in three slightly differ-ent navigation aids (NAVAIDs): VOR, VOR/DME,and VORTAC. By itself it is known as a VOR, and itprovides magnetic bearing information to and fromthe station. When DME is also installed with aVOR, the NAVAID is referred to as a VOR/DME.When military tactical air navigation (TACAN)equipment is installed with a VOR, the NAVAID isknown as a VORTAC. DME is always an integralpart of a VORTAC. Regardless of the type ofNAVAID utilized (VOR, VOR/DME or VORTAC),the VOR indicator behaves the same. Unless other-wise noted, in this section, VOR, VOR/DME andVORTAC NAVAIDs will all be referred to hereafteras VORs.

The word “omni” means all, and an omnidirectionalrange is a VHF radio transmitting ground station thatprojects straight line courses (radials) from the stationin all directions. From a top view, it can be visualizedas being similar to the spokes from the hub of a wheel.The distance VOR radials are projected depends uponthe power output of the transmitter.

The course or radials projected from the station arereferenced to magnetic north. Therefore, a radial isdefined as a line of magnetic bearing extending out-ward from the VOR station. Radials are identified bynumbers beginning with 001, which is 1° east ofmagnetic north, and progress in sequence through allthe degrees of a circle until reaching 360. To aid inorientation, a compass rose reference to magneticnorth is superimposed on aeronautical charts at thestation location.

VOR ground stations transmit within a VHF frequencyband of 108.0 – 117.95 MHz. Because the equipment isVHF, the signals transmitted are subject to line-of-sightrestrictions. Therefore, its range varies in direct propor-tion to the altitude of receiving equipment. Generally,the reception range of the signals at an altitude of 1,000feet above ground level (AGL) is about 40 to 45 miles.This distance increases with altitude. [Figure 14-26]

VORs and VORTACs are classed according to opera-tional use. There are three classes:

T (Terminal)

L (Low altitude)

H (High altitude)

The normal useful range for the various classes isshown in the following table:

VOR/VORTAC NAVAIDS

Normal Usable Altitudes and Radius DistancesDistance

Class Altitudes (Miles)

T 12,000’ and below 25L Below 18,000’ 40H Below 14,500’ 40H Within the conterminous 48 states

only, between 14,500 and 17,999’ 100H 18,000’ – FL 450 130H FL 450 – 60,000’ 100

The useful range of certain facilities may be less than50 miles. For further information concerning theserestrictions, refer to the Comm/NAVAID Remarks inthe Airport/Facility Directory.

The accuracy of course alignment of VOR radials isconsidered to be excellent. It is generally within plusor minus 1°. However, certain parts of the VOR

Neither “A” or “B”Received

“A” and “B”Signal Received

Only “A” SignalReceived

Only “B” SignalReceived

VORStation

“B”

VORStation

“A”

Figure 14-26.VHF transmissions follow a line-of-sight course.

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receiver equipment deteriorate, and this affects itsaccuracy. This is particularly true at great distancesfrom the VOR station. The best assurance of main-taining an accurate VOR receiver is periodic checksand calibrations. VOR accuracy checks are not a reg-ulatory requirement for VFR flight. However, toassure accuracy of the equipment, these checks shouldbe accomplished quite frequently along with a com-plete calibration each year. The following means areprovided for pilots to check VOR accuracy:

• FAA VOR test facility (VOT);

• certified airborne checkpoints;

• certified ground checkpoints located on airport sur-faces.

If dual VOR is installed in the airplane and tuned to thesame VOR ground facility, the maximum permissiblevariation between the two indicated bearings is 4°.

A list of these checkpoints is published in theAirport/Facility Directory.

Basically, these checks consist of verifying that theVOR radials the airplane equipment receives arealigned with the radials the station transmits. There arenot specific tolerances in VOR checks required forVFR flight. But as a guide to assure acceptable accu-racy, the required IFR tolerances can be used which are±4° for ground checks and ±6° for airborne checks.These checks can be performed by the pilot.

The VOR transmitting station can be positively identi-fied by its Morse code identification or by a recordedvoice identification which states the name of the stationfollowed by the word “VOR.” Many Flight ServiceStations transmit voice messages on the same frequencythat the VOR operates. Voice transmissions should notbe relied upon to identify stations, because many FSSsremotely transmit over several omniranges, which havedifferent names than the transmitting FSS. If the VOR isout of service for maintenance, the coded identificationis removed and not transmitted. This serves to alert pilotsthat this station should not be used for navigation. VORreceivers are designed with an alarm flag to indicatewhen signal strength is inadequate to operate the naviga-tional equipment. This happens if the airplane is too farfrom the VOR or the airplane is too low and therefore, isout of the line-of-sight of the transmitting signals.

USING THE VORIn review, for VOR radio navigation, there are twocomponents required: the ground transmitter and theairplane receiving equipment. The ground transmitteris located at a specific position on the ground and trans-

mits on an assigned frequency. The airplane equipmentincludes a receiver with a tuning device and a VOR oromninavigation instrument. The navigation instrumentconsists of (1) an omnibearing selector (OBS) some-times referred to as the course selector, (2) a coursedeviation indicator needle (Left-Right Needle), and (3)a TO-FROM indicator.

The course selector is an azimuth dial that can berotated to select a desired radial or to determine theradial over which the airplane is flying. In addition, themagnetic course “TO” or “FROM” the station can bedetermined.

When the course selector is rotated, it moves the coursedeviation indicator (CDI) or needle to indicate the posi-tion of the radial relative to the airplane. If the courseselector is rotated until the deviation needle is centered,the radial (magnetic course “FROM” the station) or itsreciprocal (magnetic course “TO” the station) can bedetermined. The course deviation needle will alsomove to the right or left if the airplane is flown or drift-ing away from the radial which is set in the courseselector.

By centering the needle, the course selector will indi-cate either the course “FROM” the station or the course“TO” the station. If the flag displays a “TO,” the courseshown on the course selector must be flown to the sta-tion.[Figure 14-27] If “FROM” is displayed and thecourse shown is followed, the airplane will be flownaway from the station.

0

36

9

121518

2124

27

30 33

TO

FR

OBS

Figure 14-27. VOR indicator.

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TRACKING WITH VORThe following describes a step-by-step procedure touse when tracking to and from a VOR station. Figure14-28 illustrates the discussion:

First, tune the VOR receiver to the frequency of theselected VOR station. For example: 115.0 to receiveBravo VOR. Next, check the identifiers to verify thatthe desired VOR is being received. As soon as the VORis properly tuned, the course deviation needle willdeflect either left or right; then rotate the azimuth dialto the course selector until the course deviation needlecenters and the TO-FROM indicates “TO.” If the nee-dle centers with a “FROM” indication, the azimuthshould be rotated 180° because, in this case, it isdesired to fly “TO” the station. Now, turn the airplaneto the heading indicated on the VOR azimuth dial orcourse selector. In this example 350°.

If a heading of 350° is maintained with a wind from theright as shown, the airplane will drift to the left of theintended track. As the airplane drifts off course, theVOR course deviation needle will gradually move tothe right of center or indicate the direction of thedesired radial or track.

To return to the desired radial, the airplane headingmust be altered to the right. As the airplane returns tothe desired track, the deviation needle will slowlyreturn to center. When centered, the airplane will be onthe desired radial and a left turn must be made toward,but not to the original heading of 350° because a winddrift correction must be established. The amount of cor-rection depends upon the strength of the wind. If thewind velocity is unknown, a trial and error method canbe used to find the correct heading. Assume, for thisexample, a 10° correction or a heading of 360° is main-tained.

While maintaining a heading of 360°, assume that thecourse deviation begins to move to the left. This meansthat the wind correction of 10° is too great and the air-plane is flying to the right of course. A slight turn to theleft should be made to permit the airplane to return tothe desired radial.

When the deviation needle centers, a small wind driftcorrection of 5° or a heading correction of 355° shouldbe flown. If this correction is adequate, the airplanewill remain on the radial. If not, small variation inheading should be made to keep the needle centered,and consequently keep the airplane on the radial.

As the VOR station is passed, the course deviation nee-dle will fluctuate, then settle down, and the “TO” indi-cation will change to “FROM.” If the airplane passes to

one side of the station, the needle will deflect in thedirection of the station as the indicator changes to“FROM.”

Generally, the same techniques apply when trackingoutbound as those used for tracking inbound. If theintent is to fly over the station and track outbound onthe reciprocal of the inbound radial, the course selectorshould not be changed. Corrections are made in thesame manner to keep the needle centered. The only dif-ference is that the omni will indicate “FROM.”

If tracking outbound on a course other than the recipro-cal of the inbound radial, this new course or radial mustbe set in the course selector and a turn made to inter-cept this course. After this course is reached, trackingprocedures are the same as previously discussed.

350°FROM

350°FROM

040°FROM

350°TO

355°

040°

355°

355°

350°TO

350°TO

350°TO

020°

350°

360°

360°

350°TO

1.

2.

3.

4.

5.

6.

7.

8.

WIND

BRAVOBRA 115.0

0

18

27 6

Figure 14-28.Tracking a radial in a crosswind.

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TIPS ON USING THE VOR

• Positively identify the station by its code or voiceidentification.

• Keep in mind that VOR signals are “line-of-sight.” A weak signal or no signal at all will bereceived if the airplane is too low or too far fromthe station.

• When navigating to a station, determine theinbound radial and use this radial. If the airplanedrifts, do not reset the course selector, but correctfor drift and fly a heading that will compensatefor wind drift.

• If minor needle fluctuations occur, avoid chang-ing headings immediately. Wait momentarily tosee if the needle recenters; if it doesn’t, thencorrect.

• When flying “TO” a station, always fly theselected course with a “TO” indication. When fly-ing “FROM” a station, always fly the selectedcourse with a “FROM” indication. If this is notdone, the action of the course deviation needle willbe reversed. To further explain this reverse action,if the airplane is flown toward a station with a“FROM” indication or away from a station with a“TO” indication, the course deviation needle willindicate in an opposite direction to that which itshould. For example, if the airplane drifts to theright of a radial being flown, the needle will moveto the right or point away from the radial. If theairplane drifts to the left of the radial being flown,the needle will move left or in the opposite direc-tion of the radial.

DISTANCE MEASURING EQUIPMENTDistance measuring equipment (DME) is an ultra highfrequency (UHF) navigational aid present withVOR/DMEs and VORTACs. It measures, in nauticalmiles (NM), the slant range distance of an airplanefrom a VOR/DME or VORTAC (both hereafterreferred to as a VORTAC). Although DME equipmentis very popular, not all airplanes are DME equipped.

To utilize DME, the pilot should select, tune, and iden-tify a VORTAC, as previously described. The DMEreceiver, utilizing what is called a “paired frequency”concept, automatically selects and tunes the UHF DMEfrequency associated with the VHF VORTAC fre-quency selected by the pilot. This process is entirelytransparent to the pilot. After a brief pause, the DMEdisplay will show the slant range distance to or fromthe VORTAC. Slant range distance is the direct dis-tance between the airplane and the VORTAC, and istherefore affected by airplane altitude. (Station passage

directly over a VORTAC from an altitude of 6,076 feetabove ground level (AGL) would show approximately1.0 NM on the DME.) DME is a very useful adjunct toVOR navigation. A VOR radial alone merely gives lineof position information. With DME, a pilot may pre-cisely locate the airplane on that line (radial).

Most DME receivers also provide groundspeedand time-to-station modes of operation. Thegroundspeed is displayed in knots (NM per hour). Thetime-to-station mode displays the minutesremaining to VORTAC station passage, predicatedupon the present groundspeed. Groundspeed andtime-to-station information is only accurate whentracking directly to or from a VORTAC. DMEreceivers typically need a minute or two of stabilizedflight directly to or from a VORTAC before dis-playing accurate groundspeed or time-to-stationinformation.

Some DME installations have a hold feature that per-mits a DME signal to be retained from one VORTACwhile the course indicator displays course deviationinformation from an ILS or another VORTAC.

VOR/DME RNAVArea navigation (RNAV) permits electronic courseguidance on any direct route between points estab-lished by the pilot. While RNAV is a generic term thatapplies to a variety of navigational aids, such asLORAN-C, GPS, and others, this section will dealwith VOR/DME-based RNAV. VOR/DME RNAV isnot a separate ground-based NAVAID, but a method ofnavigation using VOR/DME and VORTAC signalsspecially processed by the airplane’s RNAV computer.

[Figure 14-29] Note: In this section, the term “VORTAC” also

includes VOR/DME NAVAIDs.

In its simplest form, VOR/DME RNAV allows the pilotto electronically move VORTACs around to more con-venient locations. Once electronically relocated, they arereferred to as waypoints. These waypoints are describedas a combination of a selected radial and distance withinthe service volume of the VORTAC to be used. Thesewaypoints allow a straight course to be flown betweenalmost any origin and destination, without regard to theorientation of VORTACs or the existence of airways.

Area NavigationDirect Route

FIGURE 14-29. Flying an RNAV course.

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While the capabilities and methods of operation ofVOR/DME RNAV units differ, there are basic princi-pals of operation that are common to all. Pilots areurged to study the manufacturer’s operating guide andreceive instruction prior to the use of VOR/DMERNAV or any unfamiliar navigational system.Operational information and limitations should also besought from placards and the supplement section of theAirplane Flight Manual and/or Pilot’s OperatingHandbook (AFM/POH).

VOR/DME-based RNAV units operate in at least threemodes: VOR, En Route, and Approach. A fourth mode,VOR Parallel, may also be found on some models. Theunits need both VOR and DME signals to operate inany RNAV mode. If the NAVAID selected is a VORwithout DME, RNAV mode will not function.

In the VOR (or non-RNAV) mode, the unit simplyfunctions as a VOR receiver with DME capability.[Figure 14-30] The unit’s display on the VOR indicatoris conventional in all respects. For operation on estab-lished airways or any other ordinary VOR navigation,the VOR mode is used.

To utilize the unit’s RNAV capability, the pilot selectsand establishes a waypoint or a series of waypoints todefine a course. To operate in any RNAV mode, the unitneeds both radial and distance signals; therefore, aVORTAC (or VOR/DME) needs to be selected as aNAVAID. To establish a waypoint, a point somewherewithin the service range of a VORTAC is defined onthe basis of radial and distance. Once the waypoint isentered into the unit and the RNAV En Route mode isselected, the CDI will display course guidance to thewaypoint, not the original VORTAC. DME will alsodisplay distance to the waypoint. Many units have thecapability to store several waypoints, allowing them tobe programmed prior to flight, if desired, and called upin flight.

RNAV waypoints are entered into the unit in magneticbearings (radials) of degrees and tenths (i.e., 275.5°)and distances in nautical miles and tenths (i.e., 25.2NM). When plotting RNAV waypoints on an aeronau-tical chart, pilots will find it difficult to measure to thatlevel of accuracy, and in practical application, it israrely necessary. A number of flight planning publica-

tions publish airport coordinates and waypoints withthis precision and the unit will accept those figures.There is a subtle, but important difference in CDI oper-ation and display in the RNAV modes.

In the RNAV modes, course deviation is displayed interms of linear deviation. In the RNAV En Route mode,maximum deflection of the CDI typically represents 5NM on either side of the selected course, withoutregard to distance from the waypoint. In the RNAVApproach mode, maximum deflection of the CDI typi-cally represents 1 1/4 NM on either side of the selectedcourse. There is no increase in CDI sensitivity as theairplane approaches a waypoint in RNAV mode.

The RNAV Approach mode is used for instrumentapproaches. Its narrow scale width (one-quarter of theEn Route mode) permits very precise tracking to orfrom the selected waypoint. In visual flight rules (VFR)cross-country navigation, tracking a course in theApproach mode is not desirable because it requires agreat deal of attention and soon becomes tedious.

A fourth, lesser-used mode on some units is theVOR Parallel mode. This permits the CDI to displaylinear (not angular) deviation as the airplane tracksto and from VORTACs. It derives its name from per-mitting the pilot to offset (or parallel) a selectedcourse or airway at a fixed distance of the pilot’schoosing, if desired. The VOR Parallel mode has thesame effect as placing a waypoint directly over anexisting VORTAC. Some pilots select the VORParallel mode when utilizing the navigation (NAV)tracking function of their autopilot for smoothercourse following near the VORTAC.

Confusion is possible when navigating an airplanewith VOR/DME-based RNAV, and it is essentialthat the pilot become familiar with the equipmentinstalled. It is not unknown for pilots to operateinadvertently in one of the RNAV modes when theoperation was not intended by overlooking switchpositions or annunciators. The reverse has alsooccurred with a pilot neglecting to place the unitinto one of the RNAV modes by overlooking switchpositions or annunciators. As always, the prudentpilot is not only familiar with the equipment used,but never places complete reliance in just onemethod of navigation when others are available forcross-check.

AUTOMATIC DIRECTION FINDERMany general aviation-type airplanes are equippedwith automatic direction finder (ADF) radio receivingequipment. To navigate using the ADF, the pilot tunesthe receiving equipment to a ground station known as aNONDIRECTIONAL RADIOBEACON (NDB). TheNDB stations normally operate in a low or medium fre-quency band of 200 to 415 kHz. The frequencies are

FIGURE 14-30. RNAV controls.

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readily available on aeronautical charts or in theAirport/Facility Directory.

All radiobeacons except compass locators transmit acontinuous three-letter identification in code exceptduring voice transmissions. A compass locator, whichis associated with an Instrument Landing System,transmits a two-letter identification.

Standard broadcast stations can also be used in conjunc-tion with ADF. Positive identification of all radio stationsis extremely important and this is particularly true whenusing standard broadcast stations for navigation.

Nondirectional radiobeacons have one advantageover the VOR. This advantage is that low or mediumfrequencies are not affected by line-of-sight. Thesignals follow the curvature of the Earth; therefore,if the airplane is within the range of the station, thesignals can be received regardless of altitude.

The following table gives the class of NDB stations,their power, and usable range:

NONDIRECTIONAL RADIOBEACON (NDB)(Usable Radius Distances for All Altitudes)

Class Power(Watts) Distance(Miles)

Compass Locator Under 25 15MH Under 50 25H 50 – 1999 *50HH 2000 or more 75

*Service range of individual facilities may be less than50 miles.

One of the disadvantages that should be considered whenusing low frequency for navigation is that low-frequencysignals are very susceptible to electrical disturbances,such as lightning. These disturbances create excessivestatic, needle deviations, and signal fades. There may beinterference from distant stations. Pilots should know theconditions under which these disturbances can occur sothey can be more alert to possible interference whenusing the ADF.

Basically, the ADF airplane equipment consists of atuner, which is used to set the desired station frequency,and the navigational display.

The navigational display consists of a dial upon whichthe azimuth is printed, and a needle which rotatesaround the dial and points to the station to which thereceiver is tuned.

Some of the ADF dials can be rotated so as to align theazimuth with the airplane heading; others are fixedwith 0° representing the nose of the airplane, and 180°representing the tail. Only the fixed azimuth dial willbe discussed in this handbook. [Figure 14-31]

Figure 14-32 illustrates the following terms that are usedwith the ADF and should be understood by the pilot.

Relative Bearing—is the value to which the indi-cator (needle) points on the azimuth dial. Whenusing a fixed dial, this number is relative to thenose of the airplane and is the angle measuredclockwise from the nose of the airplane to a linedrawn from the airplane to the station.

Magnetic Bearing—“TO” the station is the angleformed by a line drawn from the airplane to the sta-tion and a line drawn from the airplane to magneticnorth. The magnetic bearing to the station can bedetermined by adding the relative bearing to themagnetic heading of the airplane. For example, ifthe relative bearing is 060° and the magnetic head-ing is 130°, the magnetic bearing to the station is

Figure 14-31. ADF with fixed azimuth and magnetic compass.

I I I I II I

I III

II

II

II

I

E6

3N

ADF

0

3 6

912

1518

2124

27

3033

Figure 14-32. ADF terms.

ADF

0

36

9

121518

2124

27

30 33

RadioStation

Relative Bearing

Magnetic Bearing to

Statio

n

Mag

netic

Headi

ng

Mag

netic

Nor

th

Ch 14.qxd 10/24/03 8:42 AM Page 14-23

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060° plus 130° or 190°. This means that in still aira magnetic heading of approximately 190° wouldbe flown to the station. If the total is greater than360°, subtract 360° from the total to obtain themagnetic bearing to the station. For example, if therelative bearing is 270° and magnetic heading is300°, 360° is subtracted from the total, or 570° –360° = 210°, which is the magnetic bearing to thestation.

To determine the magnetic bearing “FROM” thestation, 180° is added to or subtracted from themagnetic bearing to the station. This is the reciprocalbearing and is used when plotting position fixes.

Keep in mind that the needle of fixed azimuth points tothe station in relation to the nose of the airplane. If theneedle is deflected 30° to the left or a relative bearingof 330°, this means that the station is located 30° left. Ifthe airplane is turned left 30°, the needle will move tothe right 30° and indicate a relative bearing of 0° or theairplane will be pointing toward the station. If the pilotcontinues flight toward the station keeping the needleon 0°, the procedure is called homing to the station. If acrosswind exists, the ADF needle will continue to driftaway from zero. To keep the needle on zero, theairplane must be turned slightly resulting in a curvedflightpath to the station. Homing to the station is acommon procedure, but results in drifting downwind,thus lengthening the distance to the station.

Tracking to the station requires correcting for winddrift and results in maintaining flight along a straighttrack or bearing to the station. When the wind drift cor-rection is established, the ADF needle will indicate theamount of correction to the right or left. For instance, ifthe magnetic bearing to the station is 340°, a correctionfor a left crosswind would result in a magnetic headingof 330°, and the ADF needle would indicate 10° to theright or a relative bearing of 010°. [Figure 14-33]

When tracking away from the station, wind correctionsare made similar to tracking to the station, but the ADFneedle points toward the tail of the airplane or the 180°position on the azimuth dial. Attempting to keep theADF needle on the 180° position during winds resultsin the airplane flying a curved flight leading further andfurther from the desired track. To correct for wind whentracking outbound, correction should be made in thedirection opposite of that in which the needleis pointing.

Although the ADF is not as popular as the VOR forradio navigation, with proper precautions andintelligent use, the ADF can be a valuable aidto navigation.

LORAN-C NAVIGATIONLong Range Navigation, version C (LORAN-C) isanother form of RNAV, but one that operates fromchains of transmitters broadcasting signals in the lowfrequency (LF) spectrum. World Aeronautical Chart(WAC), Sectional Charts, and VFR Terminal AreaCharts do not show the presence of LORAN-Ctransmitters. Selection of a transmitter chain is eithermade automatically by the unit, or manually by thepilot using guidance information provided by themanufacturer. LORAN-C is a highly accurate, supple-mental form of navigation typically installed as anadjunct to VOR and ADF equipment. Databases ofairports, NAVAIDs, and air traffic control facilities arefrequently features of LORAN-C receivers.

LORAN-C is an outgrowth of the original LORAN-Adeveloped for navigation during World War II. TheLORAN-C system is used extensively in maritimeapplications. It experienced a dramatic growth inpopularity with pilots with the advent of the small,panel-mounted LORAN-C receivers available at

Figure 14-33. ADF tracking.

0 3 69

12

15

182124

27

3033

ADF

0 3 69

12

15

18212427

3033

ADF

340° Bearing

to Station

330°

330°

Ch 14.qxd 10/24/03 8:42 AM Page 14-24

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relatively low cost. These units are frequently verysophisticated and capable, with a wide variety ofnavigational functions.

With high levels of LORAN-C sophistication andcapability, a certain complexity in operation is anunfortunate necessity. Pilots are urged to read theoperating handbooks and to consult the supplementssection of the AFM/POH prior to utilizing LORAN-Cfor navigation. Many units offer so many features thatthe manufacturers often publish two different sets ofinstructions: (1) a brief operating guide and (2)in-depth operating manual.

While coverage is not global, LORAN-C signals aresuitable for navigation in all of the conterminousUnited States, and parts of Canada and Alaska. Severalforeign countries also operate their own LORAN-Csystems. In the United States, the U.S. Coast Guardoperates the LORAN-C system. LORAN-C systemstatus is available from: USCG Navigation Center,Alexandria, VA (703) 313-5900.

LORAN-C absolute accuracy is excellent—positionerrors are typically less than .25 NM. Repeatableaccuracy, or the ability to return to a waypointpreviously visited, is even better. While LORAN-C is aform of RNAV, it differs significantly fromVOR/DME-based RNAV. It operates in a 90 – 110 kHzfrequency range and is based upon measurement of thedifference in arrival times of pulses of radio frequency(RF) energy emitted by a chain of transmittershundreds of miles apart.

Within any given chain of transmitters, there is amaster station, and from three to five secondarystations. LORAN-C units must be able to receive atleast a master and two secondary stations to providenavigational information. Unlike VOR/DME-basedRNAV, where the pilot must select the appropriateVOR/DME or VORTAC frequency, there is not afrequency selection in LORAN-C. The most advancedunits automatically select the optimum chain fornavigation. Other units rely upon the pilot to select theappropriate chain with a manual entry.

After the LORAN-C receiver has been turned on, theunit must be initialized before it can be used fornavigation. While this can be accomplished in flight, itis preferable to perform this task, which can takeseveral minutes, on the ground. The methods forinitialization are as varied as the number of differentmodels of receivers. Some require pilot input duringthe process, such as verification or acknowledgment ofthe information displayed.

Most units contain databases of navigationalinformation. Frequently, such databases contain not

only airport and NAVAID locations, but also extensiveairport, airspace, and ATC information. While the unitwill operate with an expired database, the informationshould be current or verified to be correct prior to use.The pilot can update some databases, while othersrequire removal from the airplane and the services ofan avionics technician.

VFR navigation with LORAN-C can be as simple astelling the unit where the pilot wishes to go. The courseguidance provided will be a great circle (shortestdistance) route to the destination. Older units may needa destination entered in terms of latitude and longitude,but recent designs only need the identifier of the airportor NAVAID. The unit will also permit database storageand retrieval of pilot defined waypoints. LORAN-Csignals follow the curvature of the Earth andare generally usable hundreds of miles fromtheir transmitters.

The LORAN-C signal is subject to degradation from avariety of atmospheric disturbances. It is alsosusceptible to interference from static electricitybuildup on the airframe and electrically “noisy”airframe equipment. Flight in precipitation or even dustclouds can cause occasional interference withnavigational guidance from LORAN-C signals. Tominimize these effects, static wicks and bonding strapsshould be installed and properly maintained.

LORAN-C navigation information is presented to thepilot in a variety of ways. All units have self-containeddisplays, and some elaborate units feature built-inmoving map displays. Some installations can also drivean external moving map display, a conventional VORindicator, or a horizontal situation indicator (HSI).Course deviation information is presented as a lineardeviation from course—there is no increase in trackingsensitivity as the airplane approaches the waypoint ordestination. Pilots must carefully observe placards,selector switch positions, and annunciator indicationswhen utilizing LORAN-C because airplaneinstallations can vary widely. The pilot’s familiaritywith unit operation through AFM/POH supplementsand operating guides cannot be overemphasized.

LORAN-C Notices To Airmen (NOTAMs) should bereviewed prior to relying on LORAN-C for navigation.LORAN-C NOTAMs will be issued to announceoutages for specific chains and transmitters. Pilots mayobtain LORAN-C NOTAMs from FSS briefers onlyupon request.

The prudent pilot will never rely solely on one meansof navigation when others are available for backup andcross-check. Pilots should never become so dependentupon the extensive capabilities of LORAN-C that othermethods of navigation are neglected.

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GLOBAL POSITIONING SYSTEMThe global positioning system (GPS) is a satellite-based radio navigation system. Its RNAV guidance isworldwide in scope. There are no symbols for GPS onaeronautical charts as it is a space-based system withglobal coverage. Development of the system isunderway so that GPS will be capable of providing theprimary means of electronic navigation. Portable andyoke mounted units are proving to be very popular inaddition to those permanently installed in the airplane.Extensive navigation databases are common features inairplane GPS receivers.

The GPS is a satellite radio navigation and timedissemination system developed and operated by theU.S. Department of Defense (DOD). Civilian interfaceand GPS system status is available from the U.S.Coast Guard.

It is not necessary to understand the technical aspectsof GPS operation to use it in VFR/instrument flightrules (IFR) navigation. It does differ significantly fromconventional, ground-based electronic navigation, andawareness of those differences is important. Awarenessof equipment approvals and limitations is critical to thesafety of flight. The GPS system is composed of threemajor elements:

1. The space segment is composed of a constella-tion of 26 satellites orbiting approximately10,900 NM above the Earth. The operationalsatellites are often referred to as the GPSconstellation. The satellites are notgeosynchronous but instead orbit the Earth inperiods of approximately 12 hours. Eachsatellite is equipped with highly stable atomicclocks and transmits a unique code andnavigation message. Transmitting in the UHFrange means that the signals are virtuallyunaffected by weather although they aresubject to line-of-sight limitations. Thesatellites must be above the horizon (as seenby the receiver’s antenna) to be usablefor navigation.

2. The control segment consists of a mastercontrol station at Falcon AFB, ColoradoSprings, CO, five monitor stations, and threeground antennas. The monitor stations andground antennas are distributed around theEarth to allow continual monitoring andcommunications with the satellites. Updatesand corrections to the navigational messagebroadcast by each satellite are uplinkedto the satellites as they pass over theground antennas.

3. The user segment consists of all componentsassociated with the GPS receiver, rangingfrom portable, hand-held receivers to receiverspermanently installed in the airplane. Thereceiver matches the satellite’s coded signal byshifting its own identical code in a matchingprocess to precisely measure the time ofarrival. Knowing the speed the signal traveled(approximately 186,000 miles per second) andthe exact broadcast time, the distance traveledby the signal can be inferred from itsarrival time.

To solve for its location, the GPS receiver utilizes thesignals of at least four of the best-positioned satellitesto yield a three-dimensional fix (latitude, longitude,and altitude). A two-dimensional fix (latitude andlongitude only) can be determined with as few as threesatellites. GPS receivers have extensive databases.Databases are provided initially by the receivermanufacturer and updated by the manufacturer or adesignated data agency.

A wide variety of GPS receivers with extensivenavigation capabilities are available. Panel mountedunits permanently installed in the airplane may be usedfor VFR and may also have certain IFR approvals.Portable hand-held and yoke mounted GPS receiversare also popular, although these are limited to VFR use.Not all GPS receivers on the market are suited for airnavigation. Marine, recreational, and surveying units,for example, are not suitable for airplane use. As withLORAN-C receivers, GPS unit features and operatingprocedures vary widely. The pilot must be familiar withthe manufacturer’s operating guide. Placards,switch positions, and annunciators should becarefully observed.

Initialization of the unit will require several minutesand should be accomplished prior to flight. If the unithas not been operated for several months or if it hasbeen moved to a significantly different location (byseveral hundred miles) while off, this may requireseveral additional minutes. During initialization, theunit will make internal integrity checks, acquiresatellite signals, and display the database revision date.While the unit will operate with an expired database,the database should be current, or verified to becorrect, prior to relying on it for navigation.

VFR navigation with GPS can be as simple as selectinga destination (an airport, VOR, NDB, intersection, orpilot defined waypoint) and placing the unit in thenavigation mode. Course guidance provided will be agreat circle route (shortest distance) direct to thedestination. Many units provide advisory informationabout special use airspace and minimum safe altitudes,

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along with extensive airport data, and ATC services andfrequencies. Users having prior experience withLORAN-C receivers will note many similarities in thewealth of navigation information available, althoughthe technical principles of operation are quite different.

All GPS receivers have integral (built into the unit)navigation displays and some feature integral movingmap displays. Some panel-mounted units will drive aVOR indicator, HSI, or even an external moving mapdisplay. GPS course deviation is linear—there is not anincrease in tracking sensitivity as the airplaneapproaches a waypoint. Pilots must carefully observeplacards, selector switch positions, and annunciatorindications when utilizing GPS as installations andapprovals can vary widely.

The integral GPS navigation display (like mostLORAN-C units) uses several additional navigationalterms beyond those used in NDB and VOR navigation.Some of these terms, whose abbreviations vary amongmanufacturers, are shown below. The pilot shouldconsult the manufacturer’s operating guide forspecific definitions.

NOTAMs should be reviewed prior to relying on GPSfor navigation. GPS NOTAMs will be issued toannounce outages for specific GPS satellites bypseudorandom noise code (PRN) and satellite vehiclenumber (SVN). Pilots may obtain GPS NOTAMs fromFSS briefers only upon request.

When using any sophisticated and highly capablenavigation system, such as LORAN-C or GPS, there isa strong temptation to rely almost exclusively on thatunit, to the detriment of using other techniques ofposition keeping. The prudent pilot will never rely onone means of navigation when others are available forcross-check and backup.

LOST PROCEDURESGetting lost in an airplane is a potentially dangeroussituation especially when low on fuel. If a pilotbecomes lost, there are some good common senseprocedures to follow. If a town or city cannot be seen,the first thing to do is climb, being mindful of trafficand weather conditions. An increase in altitudeincreases radio and navigation reception range, andalso increases radar coverage. If flying near a town orcity, it might be possible to read the name of the townon a water tower.

If the airplane has a navigational radio, such as a VORor ADF receiver, it can be possible to determineposition by plotting an azimuth from two or morenavigational facilities. If GPS is installed, or a pilot hasa portable aviation GPS on board, it can be used todetermine the position and the location of thenearest airport.

Communicate with any available facility usingfrequencies shown on the sectional chart. If contact ismade with a controller, radar vectors may be offered.Other facilities may offer direction finding (DF)assistance. To use this procedure, the controller willrequest the pilot to hold down the transmit button for afew seconds and then release it. The controller may askthe pilot to change directions a few times and repeat thetransmit procedure. This gives the controller enoughinformation to plot the airplane position and then givevectors to a suitable landing site. If the situationbecomes threatening, transmit the situation on theemergency frequency 121.5 MHz and set thetransponder to 7700. Most facilities, and even airliners,monitor the emergency frequency.

FLIGHT DIVERSIONThere will probably come a time when a pilot will notbe able to make it to the planned destination. This canbe the result of unpredicted weather conditions, asystem malfunction, or poor preflight planning. In anycase, the pilot will need to be able to safely andefficiently divert to an alternate destination. Before anycross-country flight, check the charts for airports orsuitable landing areas along or near the route of flight.Also, check for navigational aids that can be usedduring a diversion.

Computing course, time, speed, and distanceinformation in flight requires the same computationsused during preflight planning. However, because ofthe limited cockpit space, and because attention mustbe divided between flying the airplane, makingcalculations, and scanning for other airplanes, takeadvantage of all possible shortcuts and rule-of-thumbcomputations.

When in flight, it is rarely practical to actually plot acourse on a sectional chart and mark checkpoints anddistances. Furthermore, because an alternate airport isusually not very far from your original course, actualplotting is seldom necessary.

A course to an alternate can be measured accuratelywith a protractor or plotter, but can also be measuredwith reasonable accuracy using a straightedge and thecompass rose depicted around VOR stations. Thisapproximation can be made on the basis of a radialfrom a nearby VOR or an airway that closely parallelsthe course to your alternate. However, remember thatthe magnetic heading associated with a VOR radial orprinted airway is outbound from the station. To find thecourse TO the station, it may be necessary to determinethe reciprocal of that heading. It is typically easier tonavigate to an alternate airport that has a VOR or NDBfacility on the field.

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After selecting the most appropriate alternate,approximate the magnetic course to the alternate usinga compass rose or airway on the sectional chart. If timepermits, try to start the diversion over a prominentground feature. However, in an emergency, divertpromptly toward your alternate. To complete allplotting, measuring, and computations involved beforediverting to the alternate may only aggravate anactual emergency.

Once established on course, note the time, and then usethe winds aloft nearest to your diversion point tocalculate a heading and groundspeed. Once agroundspeed has been calculated, determine a newarrival time and fuel consumption. Give priority toflying the airplane while dividing attention betweennavigation and planning. When determining an altitudeto use while diverting, consider cloud heights, winds,terrain, and radio reception.

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As a pilot, it is important to stay aware of the mentaland physical standards required for the type of flyingdone. This chapter provides information on medicalcertification and on aeromedical factors related toflying activities.

OBTAINING A MEDICAL CERTIFICATEMost pilots must have a valid medical certificate toexercise the privileges of their airman certificates.Glider and free balloon pilots are not required to holda medical certificate. Sport pilots may hold either amedical certificate or a valid state driver’s license.

To acquire a medical certificate, an examination by anaviation medical examiner (AME), a physician withtraining in aviation medicine designated by the CivilAerospace Medical Institute (CAMI), is required. Thereare three classes of medical certificates. The class ofcertificate needed depends on the type of flying the pilotplans to do.

A third-class medical is required for a private orrecreational pilot certificate. It is valid for 3 years forthose individuals who have not reached the age of 40;otherwise it is valid for 2 years. A commercial pilotcertificate requires at least a second-class medicalcertificate, which is valid for 1 year. First-class med-ical certificates are required for airline transportpilots, and are valid for 6 months.

The standards are more rigorous for the higherclasses of certificates. A pilot with a higher class

medical certificate has met the requirements for thelower classes as well. Since the class of medicalrequired applies only when exercising the privilegesof the pilot certificate for which it is required, a first-class medical would be valid for 1 year if exercisingthe privileges of a commercial certificate, and 2 or 3years, as appropriate, for exercising the privileges ofa private or recreational certificate. The same appliesfor a second-class medical certificate. The standardsfor medical certification are contained in Title 14 ofthe Code of Federal Regulations (14 CFR) part 67,and the requirements for obtaining medical certifi-cates are in 14 CFR part 61.

Students who have physical limitations, such as impairedvision, loss of a limb, or hearing impairment may be issueda medical certificate valid for “student pilot privilegesonly” while they are learning to fly. Pilots with disabilitiesmay require special equipment installed in the airplane,such as hand controls for pilots with paraplegia. Somedisabilities necessitate a limitation on the individual’scertificate; for example, impaired hearing would requirethe limitation “not valid for flight requiring the use ofradio.” When all the knowledge, experience, and profi-ciency requirements have been met and a student candemonstrate the ability to operate the airplane with thenormal level of safety, a “statement of demonstratedability” (SODA) can be issued. This waiver or SODA isvalid as long as their physical impairment does not worsen.Contact the local Flight Standards District Office (FSDO)for more information on this subject.

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ENVIRONMENTAL AND HEALTH FACTORSAFFECTING PILOT PERFORMANCEA number of health factors and physiological effects canbe linked to flying. Some are minor, while others areimportant enough to require special attention to ensuresafety of flight. In some cases, physiological factors canlead to in-flight emergencies. Some important medicalfactors that a pilot should be aware of include hypoxia,hyperventilation, middle ear and sinus problems, spatialdisorientation, motion sickness, carbon monoxide poi-soning, stress and fatigue, dehydration, and heatstroke.Other subjects include the effects of alcohol and drugs,anxiety, and excess nitrogen in the blood after scubadiving.

HYPOXIAHypoxia means “reduced oxygen” or “not enoughoxygen.” Although any tissue will die if deprived ofoxygen long enough, usually the most concern is withgetting enough oxygen to the brain, since it is particu-larly vulnerable to oxygen deprivation. Any reductionin mental function while flying can result in life-threatening errors. Hypoxia can be caused by severalfactors including an insufficient supply of oxygen,inadequate transportation of oxygen, or the inability ofthe body tissues to use oxygen. The forms of hypoxiaare divided into four major groups based on theircauses: hypoxic hypoxia, hypemic hypoxia, stagnanthypoxia, and histotoxic hypoxia.

HYPOXIC HYPOXIAHypoxic hypoxia is a result of insufficient oxygen avail-able to the lungs. A blocked airway or drowning areobvious examples of how the lungs can be deprived ofoxygen, but the reduction in partial pressure of oxygenat high altitude is an appropriate example for pilots.Although the percentage of oxygen in the atmosphere isconstant, its partial pressure decreases proportionatelyas atmospheric pressure decreases. As the airplaneascends during flight, the percentage of each gas in theatmosphere remains the same, but there are fewer mole-cules available at the pressure required for them to passbetween the membranes in the respiratory system. Thisdecrease of oxygen molecules at sufficient pressure canlead to hypoxic hypoxia.

HYPEMIC HYPOXIAThis occurs when the blood is not able to take up andtransport a sufficient amount of oxygen to the cells inthe body. Hypemic means “not enough blood.” Thistype of hypoxia is a result of oxygen deficiency in theblood, rather than a lack of inhaled oxygen, and can becaused by a variety of factors. It may be because thereis not enough blood volume (due to severe bleeding),or may result from certain blood diseases, such as ane-mia. More often it is because hemoglobin, the actualblood molecule that transports oxygen, is chemically

unable to bind oxygen molecules. The most commonform of hypemic hypoxia is carbon monoxide poison-ing. Hypemic hypoxia also can be caused by the loss ofblood from a blood donation. Blood can take severalweeks to return to normal following a donation.Although the effects of the blood loss are slight atground level, there are risks when flying during thistime.

STAGNANT HYPOXIAStagnant means “not flowing,” and stagnant hypoxiaresults when the oxygen-rich blood in the lungs isn’tmoving, for one reason or another, to the tissues thatneed it. An arm or leg going to sleep because theblood flow has accidentally been shut off is one formof stagnant hypoxia. This kind of hypoxia can alsoresult from shock, the heart failing to pump bloodeffectively, or a constricted artery. During flight,stagnant hypoxia can occur when pulling excessivepositive Gs. Cold temperatures also can reduce circu-lation and decrease the blood supplied to extremities.

HISTOTOXIC HYPOXIAThe inability of the cells to effectively use oxygen isdefined as histotoxic hypoxia. “Histo” refers to tissuesor cells, and “toxic” means poison. In this case, plentyof oxygen is being transported to the cells that need it,but they are unable to make use of it. This impairmentof cellular respiration can be caused by alcohol andother drugs, such as narcotics and poisons. Researchhas shown that drinking one ounce of alcohol canequate to about an additional 2,000 feet of physiologi-cal altitude.

SYMPTOMS OF HYPOXIAHigh-altitude flying can place a pilot in danger ofbecoming hypoxic. Oxygen starvation causes thebrain and other vital organs to become impaired. Oneparticularly noteworthy attribute of the onset ofhypoxia is the fact that the first symptoms are eupho-ria and a carefree feeling. With increased oxygenstarvation, the extremities become less responsiveand flying becomes less coordinated. The symptomsof hypoxia vary with the individual, but commonsymptoms include:

• Cyanosis (blue fingernails and lips)

• Headache

• Decreased reaction time

• Impaired judgment

• Euphoria

• Visual impairment

• Drowsiness

• Lightheaded or dizzy sensation

• Tingling in fingers and toes

• Numbness

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As hypoxia worsens, the field of vision begins tonarrow, and instrument interpretation can becomedifficult. Even with all these symptoms, the effectsof hypoxia can cause a pilot to have a false sense ofsecurity and be deceived into believing that every-thing is normal. The treatment for hypoxia includesflying at lower altitudes and/or using supplementaloxygen.

All pilots are susceptible to the effects of oxygenstarvation, regardless of physical endurance oracclimatization. When flying at high altitudes, it isparamount that oxygen be used to avoid the effectsof hypoxia. The term “time of useful consciousness”describes the maximum time the pilot has to makerational, life-saving decisions and carry them out ata given altitude without supplemental oxygen. Asaltitude increases above 10,000 feet, the symptomsof hypoxia increase in severity, and the time of use-ful consciousness rapidly decreases. [Figure 15-1]

Since symptoms of hypoxia can be different for eachindividual, the ability to recognize hypoxia can begreatly improved by experiencing and witnessing theeffects of it during an altitude chamber “flight.” TheFederal Aviation Administration (FAA) provides thisopportunity through aviation physiology training,which is conducted at the FAA Civil AerospaceMedical Institute (CAMI) and at many military facili-ties across the United States. To attend thePhysiological Training Program at CAMI, telephone(405) 954-4837 or write:

Mike Monroney Aeronautical CenterAirman Education ProgramCAMI (AAM-400)P.O. Box 25082Oklahoma City, OK 73125

HYPERVENTILATIONHyperventilation occurs when an individual is experi-encing emotional stress, fright, or pain, and thebreathing rate and depth increase, although the carbondioxide level in the blood is already at a reduced level.The result is an excessive loss of carbon dioxide fromthe body, which can lead to unconsciousness due tothe respiratory system’s overriding mechanism toregain control of breathing.

Pilots encountering an unexpected stressful situationmay unconsciously increase their breathing rate. If fly-ing at higher altitudes, either with or without oxygen, apilot may have a tendency to breathe more rapidly thannormal, which often leads to hyperventilation.

Since many of the symptoms of hyperventilation aresimilar to those of hypoxia, it is important to correctlydiagnose and treat the proper condition. If using sup-plemental oxygen, check the equipment and flow rateto ensure the symptoms are not hypoxia related.Common symptoms of hyperventilation include:

• Headache

• Decreased reaction time

• Impaired judgment

• Euphoria

• Visual impairment

• Drowsiness

• Lightheaded or dizzy sensation

• Tingling in fingers and toes

• Numbness

• Pale, clammy appearance

• Muscle spasms

Hyperventilation may produce a pale, clammyappearance and muscle spasms compared to thecyanosis and limp muscles associated with hypoxia.The treatment for hyperventilation involves restoringthe proper carbon dioxide level in the body. Breathingnormally is both the best prevention and the best curefor hyperventilation. In addition to slowing thebreathing rate, breathing into a paper bag or talkingaloud helps to overcome hyperventilation. Recoveryis usually rapid once the breathing rate is returned tonormal.

MIDDLE EAR AND SINUS PROBLEMSClimbs and descents can sometimes cause ear or sinuspain and a temporary reduction in the ability to hear.The physiological explanation for this discomfort is adifference between the pressure of the air outside the

Altitude Time of UsefulConsciousness

45,000 feet MSL

40,000 feet MSL

35,000 feet MSL

30,000 feet MSL

28,000 feet MSL

25,000 feet MSL

22,000 feet MSL

20,000 feet MSL

9 to 15 seconds

15 to 20 seconds

30 to 60 seconds

1 to 2 minutes

2 1/2 to 3 minutes

3 to 5 minutes

5 to 10 minutes

30 minutes or more

Figure 15-1.Time of useful consciousness.

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body and that of the air inside the middle ear and nasalsinuses.

The middle ear is a small cavity located in the bone ofthe skull. It is closed off from the external ear canal bythe eardrum. Normally, pressure differences betweenthe middle ear and the outside world are equalized by atube leading from inside each ear to the back of thethroat on each side, called the eustachian tube. Thesetubes are usually closed, but open during chewing,yawning, or swallowing to equalize pressure. Even aslight difference between external pressure and middleear pressure can cause discomfort. [Figure 15-2]

During a climb, middle ear air pressure may exceed thepressure of the air in the external ear canal, causing theeardrum to bulge outward. Pilots become aware of thispressure change when they experience alternate sensa-tions of “fullness” and “clearing.” During descent, thereverse happens. While the pressure of the air in theexternal ear canal increases, the middle ear cavity,which equalized with the lower pressure at altitude, isat lower pressure than the external ear canal. Thisresults in the higher outside pressure, causing theeardrum to bulge inward.

This condition can be more difficult to relieve due tothe fact that the partial vacuum tends to constrict thewalls of the eustachian tube. To remedy this oftenpainful condition, which also causes a temporaryreduction in hearing sensitivity, pinch the nostrils shut,close the mouth and lips, and blow slowly and gently inthe mouth and nose.

This procedure forces air through the eustachian tubeinto the middle ear. It may not be possible to equalizethe pressure in the ears if a pilot has a cold, an ear infec-tion, or sore throat. A flight in this condition can beextremely painful, as well as damaging to theeardrums. If experiencing minor congestion, nosedrops or nasal sprays may reduce the chance of apainful ear blockage. Before using any medication,

check with an aviation medical examiner to ensure thatit will not affect the ability to fly.

In a similar way, air pressure in the sinuses equalizeswith the pressure in the cockpit through small openingsthat connect the sinuses to the nasal passages. An upperrespiratory infection, such as a cold or sinusitis, or anasal allergic condition can produce enough congestionaround an opening to slow equalization. As the differ-ence in pressure between the sinus and the cockpitincreases, congestion may plug the opening. This “sinusblock” occurs most frequently during descent. Slowdescent rates can reduce the associated pain. A sinusblock can occur in the frontal sinuses, located aboveeach eyebrow, or in the maxillary sinuses, located ineach upper cheek. It will usually produce excruciatingpain over the sinus area. A maxillary sinus block canalso make the upper teeth ache. Bloody mucus may dis-charge from the nasal passages.

Sinus block can be avoided by not flying with an upperrespiratory infection or nasal allergic condition.Adequate protection is usually not provided by decon-gestant sprays or drops to reduce congestion around thesinus openings. Oral decongestants have side effectsthat can impair pilot performance. If a sinus block doesnot clear shortly after landing, a physician should beconsulted.

SPATIAL DISORIENTATION AND ILLUSIONSSpatial disorientation specifically refers to the lack oforientation with regard to the position, attitude, ormovement of the airplane in space. The body usesthree integrated systems working together to ascertainorientation and movement in space. The eye is by farthe largest source of information. Kinesthesia refers tothe sensation of position, movement, and tension per-ceived through the nerves, muscles, and tendons. Thevestibular system is a very sensitive motion sensingsystem located in the inner ears. It reports head posi-tion, orientation, and movement in three-dimensionalspace.

All this information comes together in the brain, andmost of the time, the three streams of information agree,giving a clear idea of where and how the body is mov-ing. Flying can sometimes cause these systems to supplyconflicting information to the brain, which can lead todisorientation. During flight in visual meteorologicalconditions (VMC), the eyes are the major orientationsource and usually prevail over false sensations fromother sensory systems. When these visual cues are takenaway, as they are in instrument meteorological condi-tions (IMC), false sensations can cause a pilot to quicklybecome disoriented.

The vestibular system in the inner ear allows thepilot to sense movement and determine orientation

MIDDLE EAR

Opening to Throat

EustachianTube

AuditoryCanal

OUTER EAR

Eardrum

Figure 15-2.The eustachian tube allows air pressure to equal-ize in the middle ear.

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in the surrounding environment. In both the left andright inner ear, three semicircular canals are posi-tioned at approximate right angles to each other.Each canal is filled with fluid and has a section fullof fine hairs. Acceleration of the inner ear in anydirection causes the tiny hairs to deflect, which inturn stimulates nerve impulses, sending messages tothe brain. The vestibular nerve transmits theimpulses from the utricle, saccule, and semicircularcanals to the brain to interpret motion. [Figure 15-3]

The postural system sends signals from the skin,joints, and muscles to the brain that are interpreted inrelation to the earth’s gravitational pull. These signalsdetermine posture. Inputs from each movementupdate the body’s position to the brain on a constantbasis. “Seat of the pants” flying is largely dependentupon these signals. Used in conjunction with visualand vestibular clues, these sensations can be fairlyreliable. However, the body cannot distinguishbetween acceleration forces due to gravity and thoseresulting from maneuvering the aircraft, which canlead to sensory illusions and false impressions of theairplane’s orientation and movement.

Under normal flight conditions, when there is avisual reference to the horizon and ground, the sen-sory system in the inner ear helps to identify thepitch, roll, and yaw movements of the airplane. Whenvisual contact with the horizon is lost, the vestibularsystem becomes unreliable. Without visual refer-ences outside the airplane, there are many situationswhere combinations of normal motions and forcescan create convincing illusions that are difficult toovercome. In a classic example, a pilot may believethe airplane is in level flight, when, in reality, it is ina gradual turn. If the airspeed increases, the pilot mayexperience a postural sensation of a level dive and

pull back on the stick, which tightens the turn andcreates increasing G-loads. If recovery is not initi-ated, a steep spiral will develop. This is sometimescalled the graveyard spiral, because if the pilot failsto recognize that the airplane is in a spiral and fails toreturn the airplane to wings-level flight, the airplanewill eventually strike the ground. If the horizonbecomes visible again, the pilot will have an oppor-tunity to return the airplane to straight-and-levelflight, and continued visual contact with the horizonwill allow the pilot to maintain straight-and-levelflight. However, if contact with the horizon is lostagain, the inner ear may fool the pilot into thinkingthe airplane has started a bank in the other direction,causing the graveyard spiral to begin all over again.

Prevention is usually the best remedy for spatial disori-entation. Unless a pilot has many hours of training ininstrument flight, flight in reduced visibility or at nightwhen the horizon is not visible should be avoided. Apilot can reduce susceptibility to disorienting illusionsthrough training and awareness, and learning to relytotally on flight instruments.

Besides the sensory illusions due to misleading inputsto the vestibular system, a pilot may also encounter var-ious visual illusions during flight. Illusions rank amongthe most common factors cited as contributing to fatalairplane accidents.

Sloping cloud formations, an obscured horizon, a darkscene spread with ground lights and stars, and certaingeometric patterns of ground light can create illusionsof not being aligned correctly with the actual horizon.Various surface features and atmospheric conditionsencountered in landing can create illusions of beingon the wrong approach path. Landing errors fromthese illusions can be prevented by anticipating them

Roll

Yaw

Pitch

Utricle

Saccule

Otoliths

Hair Cells

Cupula

Hair Cells

Ampulla of Semicircular Canal (Cross Section)

Figure 15-3.The semicircular canals lie in three planes, and sense motions of roll, pitch, and yaw.

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during approaches, inspecting unfamiliar airportsbefore landing, using electronic glide slope or VASIsystems when available, and maintaining proficiencyin landing procedures.

A narrower-than-usual runway can create the illusionthat the airplane is higher than it actually is, while awider-than-usual runway can have the opposite effect,causing the pilot to flare too high or overshoot the run-way. [Figure 15-4]

A runway that slopes up, or upsloping terrain, can cre-ate the illusion that the airplane is at a higher altitudethan it actually is, and downsloping runways or terraincan create the opposite effect. Rain on the windshieldcan create the illusion of greater height, and haze canmake distances appear greater than they are.

At sunrise or sunset, a pilot may encounter flickervertigo. In some individuals, flashing lights at certainfrequencies can trigger seizures, nausea, convulsions,or unconsciousness. Seeing the sun through a slow-moving propeller can produce the effect of a flashinglight. So can bright light reflecting off the back of thepropeller. Symptoms are rare, but be aware of thepossibility.

MOTION SICKNESSMotion sickness, or airsickness, is caused by the brainreceiving conflicting messages about the state of thebody. A pilot may experience motion sickness duringinitial flights, but it generally goes away within thefirst few lessons. Anxiety and stress, which may beexperienced at the beginning of flight training, cancontribute to motion sickness. Symptoms of motionsickness include general discomfort, nausea, dizzi-ness, paleness, sweating, and vomiting.

It is important to remember that experiencing airsick-ness is no reflection on one’s ability as a pilot. Ifprone to motion sickness, let the flight instructorknow since there are techniques that can be used toovercome this problem. For example, avoid lessons inturbulent conditions until becoming more comfortablein the airplane, or start with shorter flights and gradu-ate to longer instruction periods. If symptoms ofmotion sickness are experienced during a lesson,

opening fresh air vents, focusing on objects outsidethe airplane, and avoiding unnecessary head move-ments may help alleviate some of the discomfort.Although medications like Dramamine can preventairsickness in passengers, they are not recommendedwhile flying since they can cause drowsiness andother problems.

CARBON MONOXIDE POISONINGCarbon monoxide (CO) is a colorless and odorless gasproduced by all internal combustion engines. Since itattaches itself to the hemoglobin in the blood about 200times more easily than oxygen, carbon monoxide pre-vents the hemoglobin from carrying oxygen to the cells,resulting in hypemic hypoxia. It can take up to 48 hoursfor the body to dispose of carbon monoxide. If the poi-soning is severe enough, it can result in death. Aircraftheater vents and defrost vents may provide carbonmonoxide a passageway into the cabin, particularly ifthe engine exhaust system has a leak or is damaged. If astrong odor of exhaust gases is detected, assume that car-bon monoxide is present. However, carbon monoxidemay be present in dangerous amounts even if no exhaustodor is detected. Disposable, inexpensive carbonmonoxide detectors are widely available. In the presenceof carbon monoxide, these detectors change color to alertthe pilot of the presence of carbon monoxide. Someeffects of carbon monoxide poisoning include headache,blurred vision, dizziness, drowsiness, and/or loss ofmuscle power. Anytime a pilot smells exhaust odor, orany time that these symptoms are experienced, immedi-ate corrective actions should be taken. These includeturning off the heater, opening fresh air vents and win-dows, and using supplemental oxygen, if available.

Tobacco smoke also causes carbon monoxide poisoning.Smoking at sea level can raise the CO concentration inthe blood and result in physiological effects similar toflying at 8,000 feet. Besides hypoxia, tobacco causes dis-eases and physiological debilitation that are medicallydisqualifying for pilots.

STRESSStress is defined as the body’s response to physical andpsychological demands placed upon it. The body’sreaction to stress includes releasing chemical hormones(such as adrenaline) into the blood, and increasingmetabolism to provide more energy to the muscles. Theblood sugar, heart rate, respiration, blood pressure, andperspiration all increase. The term “stressor” is used todescribe an element that causes an individual to experi-ence stress. Examples of stressors include physicalstress (noise or vibration), physiological stress(fatigue), and psychological stress (difficult work orpersonal situations).

Stress falls into two broad categories, including acutestress (short term) and chronic stress (long term). Acute

Narrow Normal Wide

Figure 15-4. Runway Illusions.

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stress involves an immediate threat that is perceived asdanger. This is the type of stress that triggers a “fight orflight” response in an individual, whether the threat isreal or imagined. Normally, a healthy person can copewith acute stress and prevent stress overload. However,on-going acute stress can develop into chronic stress.

Chronic stress can be defined as a level of stress thatpresents an intolerable burden, exceeds the ability of anindividual to cope, and causes individual performanceto fall sharply. Unrelenting psychological pressures,such as loneliness, financial worries, and relationshipor work problems can produce a cumulative level ofstress that exceeds a person’s ability to cope with thesituation. When stress reaches these levels, perform-ance falls off rapidly. Pilots experiencing this level ofstress are not safe and should not exercise their airmanprivileges. Pilots who suspect they are suffering fromchronic stress should consult a physician.

FATIGUEFatigue is frequently associated with pilot error.Some of the effects of fatigue include degradation ofattention and concentration, impaired coordination,and decreased ability to communicate. These factorscan seriously influence the ability to make effectivedecisions. Physical fatigue can result from sleep loss,exercise, or physical work. Factors such as stress andprolonged performance of cognitive work can resultin mental fatigue.

Like stress, fatigue also falls into two broad categories:acute and chronic. Acute fatigue is short term and is anormal occurrence in everyday living. It is the kind oftiredness people feel after a period of strenuous effort,excitement, or lack of sleep. Rest after exertion and 8hours of sound sleep ordinarily cures this condition.

A special type of acute fatigue is skill fatigue. This typeof fatigue has two main effects on performance:

• Timing disruptionAppearing to perform atask as usual, but the timing of each component isslightly off. This makes the pattern of the opera-tion less smooth, because the pilot performs eachcomponent as though it were separate, instead ofpart of an integrated activity.

• Disruption of the perceptual fieldConcentrating attention upon movements orobjects in the center of vision and neglectingthose in the periphery. This may be accompaniedby loss of accuracy and smoothness in controlmovements.

Acute fatigue has many causes, but the following areamong the most important for the pilot:

• Mild hypoxia (oxygen deficiency)

• Physical stress

• Psychological stress

• Depletion of physical energy resulting from psy-chological stress

Sustained psychological stress accelerates the glandularsecretions that prepare the body for quick reactions dur-ing an emergency. These secretions make the circulatoryand respiratory systems work harder, and the liverreleases energy to provide the extra fuel needed for brainand muscle work. When this reserve energy supply isdepleted, the body lapses into generalized and severefatigue.

Acute fatigue can be prevented by a proper diet andadequate rest and sleep. A well-balanced diet preventsthe body from having to consume its own tissues as anenergy source. Adequate rest maintains the body’s storeof vital energy.

Chronic fatigue, extending over a long period of time,usually has psychological roots, although an underlyingdisease is sometimes responsible. Continuous high stresslevels, for example, can produce chronic fatigue. Chronicfatigue is not relieved by proper diet and adequate restand sleep, and usually requires treatment by a physician.An individual may experience this condition in the formof weakness, tiredness, palpitations of the heart, breath-lessness, headaches, or irritability. Sometimes chronicfatigue even creates stomach or intestinal problems andgeneralized aches and pains throughout the body. Whenthe condition becomes serious enough, it can lead toemotional illness.

If suffering from acute fatigue, stay on the ground. Iffatigue occurs in the cockpit, no amount of training orexperience can overcome the detrimental effects.Getting adequate rest is the only way to preventfatigue from occurring. Avoid flying without a fullnight’s rest, after working excessive hours, or after anespecially exhausting or stressful day. Pilots who sus-pect they are suffering from chronic fatigue shouldconsult a physician.

DEHYDRATION AND HEATSTROKEDehydration is the term given to a critical loss ofwater from the body. The first noticeable effect ofdehydration is fatigue, which in turn makes topphysical and mental performance difficult, if notimpossible. As a pilot, flying for long periods in hotsummer temperatures or at high altitudes increasesthe susceptibility of dehydration since the dry air ataltitude tends to increase the rate of water loss fromthe body. If this fluid is not replaced, fatigue pro-gresses to dizziness, weakness, nausea, tingling ofhands and feet, abdominal cramps, and extremethirst.

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Heatstroke is a condition caused by any inability of thebody to control its temperature. Onset of this conditionmay be recognized by the symptoms of dehydration,but also has been known to be recognized only bycomplete collapse.

To prevent these symptoms, it is recommended that anample supply of water be carried and used at frequentintervals on any long flight, whether thirsty or not. Ifthe airplane has a canopy or roof window, wearinglight-colored, porous clothing and a hat will help pro-vide protection from the sun. Keeping the cockpit wellventilated aids in dissipating excess heat.

ALCOHOLAlcohol impairs the efficiency of the human mecha-nism. Studies have positively proven that drinkingand performance deterioration are closely linked.Pilots must make hundreds of decisions, some of themtime-critical, during the course of a flight. The safeoutcome of any flight depends on the ability to makethe correct decisions and take the appropriate actionsduring routine occurrences, as well as abnormal situa-tions. The influence of alcohol drastically reduces thechances of completing a flight without incident. Evenin small amounts, alcohol can impair judgment,decrease sense of responsibility, affect coordination,constrict visual field, diminish memory, reduce rea-soning power, and lower attention span. As little asone ounce of alcohol can decrease the speed andstrength of muscular reflexes, lessen the efficiency ofeye movements while reading, and increase the fre-quency at which errors are committed. Impairmentsin vision and hearing occur at alcohol blood levels aslow as .01 percent.

The alcohol consumed in beer and mixed drinks isethyl alcohol, a central nervous system depressant.From a medical point of view, it acts on the body muchlike a general anesthetic. The “dose” is generally muchlower and more slowly consumed in the case of alco-hol, but the basic effects on the system are similar.Alcohol is easily and quickly absorbed by the digestivetract. The bloodstream absorbs about 80 to 90 percentof the alcohol in a drink within 30 minutes on an emptystomach. The body requires about 3 hours to rid itselfof all the alcohol contained in one mixed drink or onebeer.

With a hangover, a pilot is still under the influence ofalcohol. Although a pilot may think that he or she isfunctioning normally, the impairment of motor andmental responses still remains. Considerable amountsof alcohol can remain in the body for over 16 hours, sopilots should be cautious about flying too soon afterdrinking.

Altitude multiplies the effects of alcohol on the brain.When combined with altitude, the alcohol from two

drinks may have the same effect as three or four drinks.Alcohol interferes with the brain’s ability to utilizeoxygen, producing a form of histotoxic hypoxia. Theeffects are rapid because alcohol passes so quickly intothe bloodstream. In addition, the brain is a highly vas-cular organ that is immediately sensitive to changes inthe blood’s composition. For a pilot, the lower oxygenavailability at altitude, along with the lower capabilityof the brain to use what oxygen is there, adds up to adeadly combination.

Intoxication is determined by the amount of alcohol inthe bloodstream. This is usually measured as a percent-age by weight in the blood. 14 CFR part 91 requiresthat blood alcohol level be less than .04 percent andthat 8 hours pass between drinking alcohol and pilotingan airplane. A pilot with a blood alcohol level of .04percent or greater after 8 hours cannot fly until theblood alcohol falls below that amount. Even thoughblood alcohol may be well below .04 percent, a pilotcannot fly sooner than 8 hours after drinking alcohol.Although the regulations are quite specific, it is a goodidea to be more conservative than the regulations.

DRUGSPilot performance can be seriously degraded by bothprescribed and over-the-counter medications, as wellas by the medical conditions for which they are taken.Many medications, such as tranquilizers, sedatives,strong pain relievers, and cough-suppressants haveprimary effects that may impair judgment, memory,alertness, coordination, vision, and the ability to makecalculations. Others, such as antihistamines, bloodpressure drugs, muscle relaxants, and agents to con-trol diarrhea and motion sickness have side effectsthat may impair the same critical functions. Any med-ication that depresses the nervous system, such as asedative, tranquilizer, or antihistamine can make apilot more susceptible to hypoxia.

Pain-killers can be grouped into two broad categories:analgesics and anesthetics. Analgesics are drugs thatreduce pain, while anesthetics are drugs that deadenpain or cause loss of consciousness.

Over-the-counter analgesics, such as acetylsalicylicacid (Aspirin), acetaminophen (Tylenol), and ibupro-fen (Advil) have few side effects when taken in thecorrect dosage. Although some people are allergic tocertain analgesics or may suffer from stomach irrita-tion, flying usually is not restricted when taking thesedrugs. However, flying is almost always precludedwhile using prescription analgesics, such as Darvon,Percodan, Demerol, and codeine since these drugsmay cause side effects such as mental confusion,dizziness, headaches, nausea, and vision problems.

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Anesthetic drugs are commonly used for dental andsurgical procedures. Most local anesthetics used forminor dental and outpatient procedures wear off withina relatively short period of time. The anesthetic itselfmay not limit flying so much as the actual procedureand subsequent pain.

Stimulants are drugs that excite the central nervoussystem and produce an increase in alertness and activ-ity. Amphetamines, caffeine, and nicotine are allforms of stimulants. Common uses of these drugsinclude appetite suppression, fatigue reduction, andmood elevation. Some of these drugs may cause astimulant reaction, even though this reaction is nottheir primary function. In some cases, stimulants canproduce anxiety and mood swings, both of which aredangerous when flying.

Depressants are drugs that reduce the body’s functioningin many areas. These drugs lower blood pressure, reducemental processing, and slow motor and reactionresponses. There are several types of drugs that can causea depressing effect on the body, including tranquilizers,motion sickness medication, some types of stomach med-ication, decongestants, and antihistamines. The mostcommon depressant is alcohol.

Some drugs, which can neither be classified as stimu-lants nor depressants, have adverse effects on flying.For example, some forms of antibiotics can producedangerous side effects, such as balance disorders,hearing loss, nausea, and vomiting. While manyantibiotics are safe for use while flying, the infectionrequiring the antibiotic may prohibit flying. In addi-tion, unless specifically prescribed by a physician, donot take more than one drug at a time, and never mixdrugs with alcohol, because the effects are oftenunpredictable.

The dangers of illegal drugs also are well documented.Certain illegal drugs can have hallucinatory effects thatoccur days or weeks after the drug is taken. Obviously,these drugs have no place in the aviation community.

The Code of Federal Regulations prohibits pilots fromperforming crewmember duties while using any med-ication that affects the faculties in any way contrary tosafety. The safest rule is not to fly as a crewmemberwhile taking any medication, unless approved to do soby the FAA. If there is any doubt regarding the effectsof any medication, consult an aviation medical exam-iner before flying.

SCUBA DIVINGScuba diving subjects the body to increased pressure,which allows more nitrogen to dissolve in body tissuesand fluids. The reduction of atmospheric pressure that

accompanies flying can produce physical problems forscuba divers. Reducing the pressure too quickly allowssmall bubbles of nitrogen to form inside the body asthe gas comes out of solution. These bubbles can causea painful and potentially incapacitating conditioncalled “the bends.” (An example is dissolved gas form-ing bubbles as pressure decreases by slowly opening atransparent bottle of soda.) Scuba training emphasizeshow to prevent the bends when rising to the surface,but increased nitrogen concentrations can remain in tis-sue fluids for several hours after a diver leaves thewater. The bends can be experienced from as low as8,000 feet MSL, with increasing severity as altitudeincreases. As noted in the Aeronautical InformationManual (AIM), the minimum recommended timebetween scuba diving on nondecompression stop divesand flying is 12 hours, while the minimum time recom-mended between decompression stop diving and flyingis 24 hours. [Figure 15-5]

VISION IN FLIGHTOf all the senses, vision is the most important for safeflight. Most of the things perceived while flying arevisual or heavily supplemented by vision. As remarkableand vital as it is, vision is subject to some limitations,such as illusions and blind spots. The more a pilot under-stands about the eyes and how they function, the easier itis to use vision effectively and compensate for potentialproblems.

The eye functions much like a camera. Its structureincludes an aperture, a lens, a mechanism for focusing,and a surface for registering images. Light enters

Figure 15-5. Scuba divers must not fly for specific time peri-ods following dives to avoid the bends.

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through the cornea at the front of the eyeball, travelsthrough the lens and falls on the retina. The retina con-tains light sensitive cells that convert light energy intoelectrical impulses that travel through nerves to thebrain. The brain interprets the electrical signals to formimages. There are two kinds of light sensitive cells inthe eyes: rods and cones. [Figure 15-6]

The cones are responsible for all color vision, fromappreciating a glorious sunset to discerning the subtleshades in a fine painting. Cones are present throughoutthe retina, but are concentrated toward the center of thefield of vision at the back of the retina. There is a smallpit called the fovea where almost all the light sensingcells are cones. This is the area where most “looking”occurs (the center of the visual field where detail, colorsensitivity, and resolution are highest).

While the cones and their associated nerves are wellsuited to detecting fine detail and color in high lightlevels, the rods are better able to detect movement andprovide vision in dim light. The rods are unable to dis-cern color but are very sensitive in low light levels.The trouble with rods is that a large amount of lightoverwhelms them, and they take a long time to “reset”and adapt to the dark again. There are so many conesin the fovea that the very center of the visual fieldhardly has any rods at all. So in low light, the middleof the visual field isn’t very sensitive, but farther fromthe fovea, the rods are more numerous and providethe major portion of night vision.

The area where the optic nerve enters the eyeball hasno rods or cones, leaving a blind spot in the field ofvision. Normally, each eye compensates for the other’sblind spot. Figure 15-7 provides a dramatic example ofthe eye’s blind spot. Cover the right eye and hold this

page at arm’s length. Focus the left eye on the X in theright side of the windshield and notice what happens tothe airplane while slowly bringing the page closer tothe eye.

EMPTY-FIELD MYOPIAAnother problem associated with flying at night, ininstrument meteorological conditions and/or reducedvisibility is empty-field myopia, or induced nearsighted-ness. With nothing to focus on, the eyes automaticallyfocus on a point just slightly ahead of the airplane.Searching out and focusing on distant light sources, nomatter how dim, helps prevent the onset of empty-fieldmyopia.

NIGHT VISIONIt is estimated that once fully adapted to darkness, therods are 10,000 times more sensitive to light than thecones, making them the primary receptors for nightvision. Since the cones are concentrated near the fovea,the rods are also responsible for much of the peripheralvision. The concentration of cones in the fovea can makea night blind spot in the center of the field of vision. Tosee an object clearly at night, the pilot must expose therods to the image. This can be done by looking 5° to 10°off center of the object to be seen. This can be tried in a

The rods and cones (film) of the retina are the receptors which record the image and transmit it through the optic nerve to the brain for interpretation.

Light passes through the cornea (the transparent window on the front of the eye) and then through the lens to focus on the retina.

The pupil (aperture) is the opening at the center of the iris. The size of the pupil is adjusted to control the amount of light entering the eye.

Lens

Iris

Pupil

Cornea

Optic Nerve Retina

Rods and Cones

Fovea(All Cones)

Rod Concentration

Figure 15-6.The eye.

Figure 15-7.The eye’s blind spot.

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dim light in a darkened room. When looking directly atthe light, it dims or disappears altogether. When lookingslightly off center, it becomes clearer and brighter.

Refer to figure 15-8. When looking directly at anobject, the image is focused mainly on the fovea, wheredetail is best seen. At night, the ability to see an objectin the center of the visual field is reduced as the coneslose much of their visual acuity and the rods becomemore sensitive. Looking off center can help compen-sate for this night blind spot. Along with the loss ofsharpness and color at night, depth perception andjudgment of size may be lost.

While the cones adapt rapidly to changes in light inten-sities, the rods take much longer. Walking from brightsunlight into a dark movie theater is an example of thisdark adaptation period experience. The rods can takeapproximately 30 minutes to fully adapt to the dark. Abright light, however, can completely destroy nightadaptation, leaving night vision severely compromisedwhile the adaptation process is repeated.

Several things can be done to keep the eyes adapted tothe dark. The first is obvious: avoid bright lights beforeand during the flight. For 30 minutes before a nightflight, avoid any bright light sources, such as head-lights, landing lights, strobe lights, or flashlights. If abright light is encountered, close one eye to keep itlight sensitive. This allows the use of that eye to seeagain once the light is gone.

Red cockpit lighting also helps preserve night vision, butred light severely distorts some colors and completelywashes out the color red. This makes reading an aero-nautical chart difficult. A dim white light or a carefully

directed flashlight can enhance night reading ability.While flying at night, keep the instrument panel and inte-rior lights turned up no higher than necessary. This helpsto see outside references more easily. If the eyes becomeblurry, blinking more frequently often helps.

Diet and general physical health have an impact onhow well a pilot can see in the dark. Deficiencies invitamins A and C have been shown to reduce night acu-ity. Other factors, such as carbon monoxide poisoning,smoking, alcohol, certain drugs, and a lack of oxygenalso can greatly decrease night vision.

NIGHT VISUAL ILLUSIONSThere are many different types of visual illusions thatcommonly occur at night. Anticipating and stayingaware of them is usually the best way to avoid them.

AUTOKINESISAutokinesis is caused by staring at a single point of lightagainst a dark background for more than a few seconds.After a few moments, the light appears to move on itsown. To prevent this illusion, focus the eyes on objects atvarying distances and avoid fixating on one target. Besure to maintain a normal scan pattern.

FALSE HORIZONA false horizon can occur when the natural horizon isobscured or not readily apparent. It can be generated byconfusing bright stars and city lights. It can also occurwhile flying toward the shore of an ocean or a largelake. Because of the relative darkness of the water, thelights along the shoreline can be mistaken for stars inthe sky. [Figure 15-9]

Cones Active

Rods Active Night Blind Spot

Figure 15-8. Night blind spot.

Apparent Horizon

Actual H

orizon

Figure 15-9. At night, the horizon may be hard to discern dueto dark terrain and misleading light patterns on the ground.

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NIGHT LANDING ILLUSIONSLanding illusions occur in many forms. Above feature-less terrain at night, there is a natural tendency to fly alower-than-normal approach. Elements that cause anytype of visual obscuration, such as rain, haze, or a darkrunway environment also can cause low approaches.Bright lights, steep surrounding terrain, and a wide run-way can produce the illusion of being too low, with a

tendency to fly a higher-than-normal approach.Often a set of regularly spaced lights along a road orhighway can appear to be runway lights. Pilots haveeven mistaken the lights on moving trains as runwayor approach lights. Bright runway or approach light-ing systems can create the illusion that the airplaneis closer to the runway, especially where few lightsilluminate the surrounding terrain.

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Aeronautical decision making (ADM) is a systematicapproach to the mental process used by airplane pilotsto consistently determine the best course of action inresponse to a given set of circumstances. The impor-tance of learning effective ADM skills cannot beoveremphasized. While progress is continually beingmade in the advancement of pilot training methods, air-plane equipment and systems, and services for pilots,accidents still occur. Despite all the changes in technol-ogy to improve flight safety, one factor remains thesamethe human factor. It is estimated that approxi-mately 75 percent of all aviation accidents are humanfactors related.

Historically, the term “pilot error” has been used todescribe the causes of these accidents. Pilot errormeans that an action or decision made by the pilot wasthe cause, or a contributing factor that led to the acci-dent. This definition also includes the pilot’s failure tomake a decision or take action. From a broader per-spective, the phrase “human factors related” more aptlydescribes these accidents since it is usually not a singledecision that leads to an accident, but a chain of eventstriggered by a number of factors.

The poor judgment chain, sometimes referred to as the“error chain,” is a term used to describe this concept ofcontributing factors in a human factors-related acci-

dent. Breaking one link in the chain normally is all thatis necessary to change the outcome of the sequence ofevents. The following is an example illustrating thepoor judgment chain.

A private pilot with around 350 hours was ferrying anairplane cross-country to a new owner. Due to timeconstraints, the pilot skipped dinner the night beforeand had no breakfast on the morning of the flight. Thepilot planned to have lunch around noon at a fuel stop.

A descent was begun from 9,500 feet, about 20 milesfrom the chosen fuel stop, due to haze and unfamiliaritywith the area. When the airplane arrived at pattern alti-tude, the pilot could not find the airport. The pilot thencircled north of the town, then back over the town, thenflew to the west, then turned back to the east.

The pilot decided to check for airport information inthe Airport/Facility Directory, which was on the rearseat and not readily available.

Power had not been increased since the descent topattern altitude, and the pilot had been holding backpressure on the yoke. While attempting to retrieve theAirport/Facility Directory, a loud “bang” was heard.Looking up, the pilot discovered the airplane was onlyabout 200 feet above ground level. Increasing power,the pilot climbed and located the airport. After land-ing, it was discovered a fiberglass antenna had beenhit, which damaged the leading edge of the left wing.

By discussing the events that led to this accident, itcan be understood how a series of judgmental errors

Human Factors—The study of how people interact with their envi-ronments. In the case of general aviation, it is the study of how pilotperformance is influenced by such issues as the design of cockpits,the function of the organs of the body, the effects of emotions, andthe interaction and communication with the other participants ofthe aviation community, such as other crewmembers and air trafficcontrol personnel.

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contributed to the final outcome of this flight. Forexample, one of the first elements that affected thepilot’s flight was fatigue. The pilot understood thatfatigue and hunger could affect the ability to flysafely, but let the desire to stay on schedule overridethe concern for a safe flight.

Next, the rush to get airborne led the pilot to skip orpostpone necessary aspects of preflight planning.Research before takeoff, with a quick review beforedescent, could have ensured a clear mental picture ofthe location of the airport in relation to the town.Copying relevant information from flight guides andother information sources is part of careful preflightplanning. Studying the aeronautical charts and check-ing the Notices to Airmen (NOTAM) beforehandwould have alerted the pilot to towers, terrain, andother obstructions in the vicinity of the airport.

Even without proper planning before the flight, goodcockpit resource management and organization wouldhave had the flight guide and any other necessary infor-mation near at hand, perhaps with the relevant pagesflagged. Approaching the airport environment and fly-ing around the area at traffic pattern altitude in hazyconditions could have interfered with other air traffic,and the potential for a midair collision is obvious.

In all circumstances, the pilot’s first duty is to fly theairplane. Clearly that would include adjusting thepower, setting the trim, and keeping track of altitude.This pilot was extremely fortunate—the outcome couldeasily have been fatal.

On numerous occasions during the flight, the pilot couldhave made effective decisions that would have brokenthe chain of error and prevented this accident. Makingsound decisions is the key to preventing accidents.Traditional pilot training has emphasized flying skills,knowledge of the airplane, and familiarity with regula-tions. ADM training focuses on the decision-makingprocess and the factors that affect a pilot’s ability tomake effective choices.

ORIGINS OF ADM TRAININGThe airlines developed some of the first trainingprograms that focused on improving aeronauticaldecision making. Human factors-related accidentsmotivated the airline industry to implement crewresource management (CRM) training for flightcrews. The focus of CRM programs is the effectiveuse of all available resources; human resources,hardware, and information. Human resourcesinclude all groups routinely working with the cock-pit crew (or pilot) who are involved in decisionsthat are required to operate a flight safely. Thesegroups include, but are not limited to: dispatchers,cabin crewmembers, maintenance personnel, and

air traffic controllers. Although the CRM conceptoriginated as airlines developed ways of facilitatingcrew cooperation to improve decision making in thecockpit, CRM principles, such as workload manage-ment, situational awareness, communication, theleadership role of the captain, and crewmembercoordination have direct application to the generalaviation cockpit. This also includes single pilotoperations since pilots of small airplanes, as well ascrews of larger airplanes, must make effective useof all available resources—human resources, hard-ware, and information. AC 60-22, AeronauticalDecision Making, provides background references,definitions, and other pertinent information aboutADM training in the general aviation environment.[Figure 16-1]

THE DECISION-MAKING PROCESSAn understanding of the decision-making processprovides a pilot with a foundation for developingADM skills. Some situations, such as engine fail-ures, require a pilot to respond immediately usingestablished procedures with little time for detailedanalysis. Traditionally, pilots have been well trainedto react to emergencies, but are not as well preparedto make decisions requiring a more reflectiveresponse. Typically during a flight, there is time toexamine any changes that occur, gather information,and assess risk before reaching a decision. The stepsleading to this conclusion constitute the decision-making process.

DEFINING THE PROBLEMProblem definition is the first step in the decision-making process. Defining the problem begins withrecognizing that a change has occurred or that anexpected change did not occur. A problem is perceivedfirst by the senses, then is distinguished throughinsight and experience. These same abilities, as well asan objective analysis of all available information, areused to determine the exact nature and severity of theproblem.

One critical error that can be made during the deci-sion-making process is incorrectly defining theproblem. For example, a low oil pressure readingcould indicate that the engine is about to fail and anemergency landing should be planned, or it couldmean that the oil pressure sensor has failed. Theactions to be taken in each of these circumstanceswould be significantly different. Fixating on aproblem that does not exist can divert attentionfrom important tasks. The pilot’s failure to main-tain an awareness of the circumstances regardingthe flight now becomes the problem. This is whyonce an initial assumption is made regarding theproblem, other sources must be used to verify thatthe conclusion is correct.

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While on a cross-country flight, a pilot discovered thatfuel consumption was significantly higher than predictedduring flight planning. By noticing this discrepancy,change has been recognized. Based on insight, cross-country flying experience, and knowledge of airplanesystems, the pilot considers the possibility that theremight be enough fuel to reach the destination. Factorsthat may increase the fuel burn rate could includeenvironmental factors, such as higher-than-expectedheadwinds and lower-than-expected groundspeed. Todetermine the severity of the problem, recalculate thefuel consumption and reassess fuel requirements.

CHOOSING A COURSE OF ACTIONAfter the problem has been identified, the pilot mustevaluate the need to react to it and determine theactions that may be taken to resolve the situation in the

time available. The expected outcome of each possibleaction should be considered and the risks assessedbefore deciding on a response to the situation.

The pilot determines there is insufficient fuel to reachthe destination, and considers other options, such asturning around and landing at a nearby airport thathas been passed, diverting off course, or landing priorto the destination at an airport on the route. Theexpected outcome of each possible action must beconsidered along with an assessment of the risksinvolved. After studying the aeronautical chart, thepilot concludes that there is an airport that has fuel-ing services within the remaining fuel range along theroute. The time expended for the extra fuel stop is aworthwhile investment to ensure a safe completion ofthe flight.

DEFINITIONS

AERONAUTICAL DECISION MAKING (ADM) is a systematic approach to the mental process used by pilots to consistently determine the best course of action in response to a given set of circumstances.

ATTITUDE is a personal motivational predisposition to respond to persons, situations, or events in a given manner that can, nevertheless, be changed or modified through training as sort of a mental shortcut to decision making.

ATTITUDE MANAGEMENT is the ability to recognize hazardous attitudes in oneself and the willingness to modify them as necessary through the application of an appropriate antidote thought.

HEADWORK is required to accomplish a conscious, rational thought process when making decisions. Good decision making involves risk identification and assessment, information processing, and problem solving.

JUDGMENT is the mental process of recognizing and analyzing all pertinent information in a particular situation, a rational evaluation of alternative actions in response to it, and a timely decision on which action to take.

PERSONALITY is the embodiment of personal traits and characteristics of an individual that are set at a very early age and extremely resistant to change.

POOR JUDGMENT CHAIN is a series of mistakes that may lead to an accident or incident. Two basic principles generally associated with the creation of a poor judgment chain are: (1) One bad decision often leads to another; and (2) as a string of bad decisions grows, it reduces the number of subsequent alternatives for continued safe flight. ADM is intended to break the poor judgment chain before it can cause an accident or incident.

RISK ELEMENTS IN ADM take into consideration the four fundamental risk elements: the pilot, the aircraft, the environment, and the type of operation that comprise any given aviation situation.

RISK MANAGEMENT is the part of the decision making process which relies on situational awareness, problem recognition, and good judgment to reduce risks associated with each flight.

SITUATIONAL AWARENESS is the accurate perception and understanding of all the factors and conditions within the four fundamental risk elements that affect safety before, during, and after the flight.

SKILLS and PROCEDURES are the procedural, psychomotor, and perceptual skills used to control a specific aircraft or its systems. They are the airmanship abilities that are gained through conventional training, are perfected, and become almost automatic through experience.

STRESS MANAGEMENT is the personal analysis of the kinds of stress experienced while flying, the application of appropriate stress assessment tools, and other coping mechanisms.

CREW RESOURCE MANAGEMENT (CRM) is the application of team management concepts in the flight deck environment. It was initially known as cockpit resource management, but as CRM programs evolved to include cabin crews, maintenance personnel, and others, the phrase crew resource management was adopted. This includes single pilots, as in most general aviation aircraft. Pilots of small aircraft, as well as crews of larger aircraft, must make effective use of all available resources; human resources, hardware, and information. A current definition includes all groups routinely working with the cockpit crew who are involved in decisions required to operate a flight safely. These groups include, but are not limited to: pilots, dispatchers, cabin crewmembers, maintenance personnel, and air traffic controllers. CRM is one way of addressing the challenge of optimizing the human/machine interface and accompanying interpersonal activities.

Figure 16-1.These terms are used in AC 60-22 to explain concepts used in ADM training.

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IMPLEMENTING THE DECISION ANDEVALUATING THE OUTCOMEAlthough a decision may be reached and a course ofaction implemented, the decision-making process is notcomplete. It is important to think ahead and determinehow the decision could affect other phases of the flight.As the flight progresses, the pilot must continue toevaluate the outcome of the decision to ensure that it isproducing the desired result.

To implement the decision, the pilot determines thenecessary course changes and calculates a new esti-mated time of arrival, as well as contacts the nearestflight service station to amend the flight plan andcheck weather conditions at the fuel stop. Proceedingto the airport, continue to monitor the groundspeed,fuel status, and the weather conditions to ensure thatno additional steps need to be taken to guarantee thesafety of the flight.

The decision-making process normally consists of sev-eral steps before choosing a course of action. To helpremember the elements of the decision-makingprocess, a six-step model has been developed using theacronym “DECIDE.” [Figure 16-2]

RISK MANAGEMENTDuring each flight, decisions must be made regardingevents involving interactions between the four riskelements—the pilot in command, the airplane, theenvironment, and the operation. The decision-makingprocess involves an evaluation of each of these riskelements to achieve an accurate perception of theflight situation. [Figure 16-3]

One of the most important decisions that a pilot incommand must make is the go/no-go decision.Evaluating each of these risk elements can help indeciding whether a flight should be conducted or con-tinued. Below is a review of the four risk elements andhow they affect decision making regarding the follow-ing situations.

Pilot—A pilot must continually make decisions aboutcompetency, condition of health, mental and emotionalstate, level of fatigue, and many other variables. Forexample, a pilot may be called early in the morning tomake a long flight. If a pilot has had only a few hoursof sleep and is concerned that the congestion beingexperienced could be the onset of a cold, it would beprudent to consider if the flight could be accomplishedsafely.

A pilot had only 4 hours of sleep the night before. Theboss then asked the pilot to fly to a meeting in a city750 miles away. The reported weather was marginaland not expected to improve. After assessing fitness asa pilot, it was decided that it would not be wise to makethe flight. The boss was initially unhappy, but laterconvinced by the pilot that the risks involved wereunacceptable.

Airplane—A pilot will frequently base decisions onthe evaluations of the airplane, such as performance,equipment, or airworthiness.

Detect the fact that a change has occurred.

Estimate the need to counter or react to the change.

Choose a desirable outcome for the success of the flight.

Identify actions which could successfully control the change.

Do the necessary action to adapt to the change.

Evaluate the effect of the action.

DECIDE MODEL

Figure 16-2. The DECIDE model can provide a framework foreffective decision making.

RISK ELEMENTSPilot Airplane Environment Operation

Factors, such as weather, airport conditions, and the availability of air traffic control services must be examined.

The airplane's performance, limitations, equipment, and airworthiness must be deter- mined.

The pilot's fitness to fly must be evaluated including competency in the airplane, currency, and flight experience.

To maintain situational awareness, an accurate perception must be attained of how the pilot, airplane, environment, and operation combine to affect the flight.

Situation

The purpose of the flight is a factor which influences the pilot's decision on undertaking or continuing the flight.

Figure 16-3. When situationally aware, the pilot has an overview of the total operation and is not fixated on one perceived sig-nificant factor.

Risk Elements—The four components of a flight that make up theoverall situation.

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During a preflight, a pilot noticed a small amount of oildripping from the bottom of the cowling. Although thequantity of oil seemed insignificant at the time, the pilotdecided to delay the takeoff and have a mechanic checkthe source of the oil. The pilot’s good judgment wasconfirmed when the mechanic found that one of the oilcooler hose fittings was loose.

Environment—This encompasses many elements notpilot or airplane related. It can include such factors asweather, air traffic control, navaids, terrain, takeoff andlanding areas, and surrounding obstacles. Weather isone element that can change drastically over time anddistance.

A pilot was landing a small airplane just after a heavyjet had departed a parallel runway. The pilot assumedthat wake turbulence would not be a problem sincelandings had been performed under similar circum-stances. Due to a combination of prevailing winds andwake turbulence from the heavy jet drifting across thelanding runway, the airplane made a hard landing. Thepilot made an error when assessing the flight environ-ment.

Operation—The interaction between the pilot, air-plane, and the environment is greatly influenced bythe purpose of each flight operation. The pilot mustevaluate the three previous areas to decide on thedesirability of undertaking or continuing the flight asplanned. It is worth asking why the flight is beingmade, how critical is it to maintain the schedule, andis the trip worth the risks?

On a ferry flight to deliver an airplane from the factory,in marginal weather conditions, the pilot calculated thegroundspeed and determined that the airplane wouldarrive at the destination with only 10 minutes of fuelremaining. The pilot was determined to keep on sched-ule by trying to “stretch” the fuel supply instead oflanding to refuel. After landing with low fuel state, thepilot realized that this could have easily resulted in anemergency landing in deteriorating weather condi-tions. This was a chance that was not worth taking tokeep the planned schedule.

ASSESSING RISKExamining National Transportation Safety Board(NTSB) reports and other accident research can helpassess risk more effectively. For example, the accidentrate during night VFR decreases by nearly 50 percentonce a pilot obtains 100 hours, and continues todecrease until the 1,000-hour level. The data suggestthat for the first 500 hours, pilots flying VFR at nightmight want to establish higher personal limitations thanare required by the regulations and, if applicable, applyinstrument flying skills in this environment. [Figure16-4]

Studies also indicate the types of flight activities thatare likely to result in the most serious accidents. Themajority of fatal general aviation accidents fall underthe categories of takeoff/initial climb, maneuveringflight, approaches, and weather. Delving deeper intoaccident statistics can provide some important detailsthat can help in understanding the risks involved withspecific flying situations. For example, maneuveringflight is one of the largest single producers of fatalaccidents. In the approach phase, fatal accidents oftenhappen at night or in IFR conditions. Takeoff/initialclimb accidents frequently are due to the pilot’s lackof awareness of the effects of density altitude on air-plane performance or other improper takeoff planningresulting in loss of control during, or shortly aftertakeoff. The majority of weather-related accidentsoccur after attempted VFR flight into IFR conditions.

FACTORS AFFECTING DECISIONMAKINGIt is important to point out the fact that being familiarwith the decision-making process does not ensure thegood judgment to be a safe pilot. The ability to makeeffective decisions as pilot in command depends on anumber of factors. Some circumstances, such as thetime available to make a decision may be beyond apilot’s control. However, one can learn to recognizethose factors that can be managed, and learn skills toimprove decision-making ability and judgment.

PILOT SELF-ASSESSMENTThe pilot in command of an airplane is directlyresponsible for, and is the final authority as to, theoperation of that airplane. To effectively exercise thatresponsibility and make effective decisions regardingthe outcome of a flight, a pilot should be aware of per-sonal limitations. Performance during a flight is

<51 101 201 501 <1000 <2000 10,000 TotalPilot's Total Time (Hours)

40

30

20

10

Nig

ht V

FR

Acc

iden

t Rat

eP

er 1

00,0

00 H

ours

Figure 16-4. Statistical data can identify operations that havemore risk involved.

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affected by many factors, such as health, recency ofexperience, knowledge, skill level, and attitude.

Exercising good judgment begins prior to taking the con-trols of an airplane. Often, pilots thoroughly check theirairplane to determine airworthiness, yet do not evaluatetheir own fitness for flight. Just as a checklist is usedwhen preflighting an airplane, a personal checklist basedon such factors as experience, currency, and comfort levelcan help determine if a pilot is prepared for a particularflight. Specifying when refresher training should beaccomplished and designating weather minimumsthat may be higher than those listed in Title 14 of theCode of Federal Regulations (14 CFR) part 91 areelements that may be included on a personal check-list. In addition to a review of personal limitations,use the I’M SAFE Checklist to further evaluate fitnessfor flight. [Figure 16-5]

RECOGNIZING HAZARDOUS ATTITUDESBeing fit to fly depends on more than just a pilot’sphysical condition and recency of experience. Forexample, attitude will affect the quality of decisions.Attitude can be defined as a personal motivationalpredisposition to respond to persons, situations, orevents in a given manner. Studies have identified fivehazardous attitudes that can interfere with the abilityto make sound decisions and exercise authority prop-erly. [Figure 16-6]

Hazardous attitudes can lead to poor decision makingand actions that involve unnecessary risk. The pilotmust examine decisions carefully to ensure that thechoices have not been influenced by hazardous atti-tudes and be familiar with positive alternatives tocounteract the hazardous attitudes. These substitute

attitudes are referred to as antidotes. During a flightoperation, it is important to be able to recognize ahazardous attitude, correctly label the thought, andthen recall its antidote. [Figure 16-7]

STRESS MANAGEMENTEveryone is stressed to some degree almost all thetime. A certain amount of stress is good since it keepsa person alert and prevents complacency. However,effects of stress are cumulative and, if not coped withadequately, they eventually add up to an intolerableburden. Performance generally increases with theonset of stress, peaks, and then begins to fall off rap-

Illness—Do I have any symptoms?

Medication—Have I been taking prescription or over-the-counter drugs?

Stress—Am I under psychological pressure from the job? Worried about financial matters, health problems, or family discord?

Fatigue—Am I tired and not adequately rested?

Eating—Am I adequately nourished?

Alcohol—Have I been drinking within 8 hours? Within 24 hours?

I'M SAFE CHECKLIST

Figure 16-5. Prior to flight, pilot fitness should be assessedthe same as the airplane’s airworthiness is evaluated.

THE FIVE HAZARDOUS ATTITUDES

1. Anti-Authority: "Don't tell me."

This attitude is found in people who do not like anyone telling them what to do. In a sense, they are saying, "No one can tell me what to do." They may be resentful of having someone tell them what to do, or may regard rules, regulations, and procedures as silly or unnecessary. However, it is always your prerogative to question authority if you feel it is in error.

This is the attitude of people who frequently feel the need to do something, anything, immediately. They do not stop to think about what they are about to do; they do not select the best alternative, and they do the first thing that comes to mind.

Many people feel that accidents happen to others, but never to them. They know accidents can happen, and they know that anyone can be affected. They never really feel or believe that they will be personally involved. Pilots who think this way are more likely to take chances and increase risk.

Pilots who are always trying to prove that they are better than anyone else are thinking, "I can do it –I'll show them." Pilots with this type of attitude will try to prove themselves by taking risks in order to impress others. While this pattern is thought to be a male characteristic, women are equally susceptible.

Pilots who think, "What's the use?" do not see themselves as being able to make a great deal of difference in what happens to them. When things go well, the pilot is apt to think that it is good luck. When things go badly, the pilot may feel that someone is out to get me, or attribute it to bad luck. The pilot will leave the action to others, for better or worse. Sometimes, such pilots will even go along with unreasonable requests just to be a "nice guy."

2. Impulsivity: "Do it quickly."

3. Invulnerability: "It won't happen to me."

4. Macho: "I can do it."

5. Resignation: "What's the use?"

Figure 16-6. The pilot should examine decisions carefully to ensure that the choices have not been influenced by a hazardousattitude.

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idly as stress levels exceed a person’s ability to cope.The ability to make effective decisions during flightcan be impaired by stress. Factors, referred to asstressors, can increase a pilot’s risk of error in thecockpit. [Figure 16-8]

There are several techniques to help manage the accu-mulation of life stresses and prevent stress overload. Forexample, including relaxation time in a busy scheduleand maintaining a program of physical fitness can helpreduce stress levels. Learning to manage time moreeffectively can help avoid heavy pressures imposed bygetting behind schedule and not meeting deadlines.Take a self-assessment to determine capabilities andlimitations and then set realistic goals. In addition,avoiding stressful situations and encounters can help tocope with stress.

USE OF RESOURCESTo make informed decisions during flight operations, apilot must become aware of the resources found bothinside and outside the cockpit. Since useful tools andsources of information may not always be readilyapparent, learning to recognize these resources is anessential part of ADM training. Resources must notonly be identified, but a pilot must develop the skills toevaluate whether there is time to use a particularresource and the impact that its use will have upon thesafety of flight. For example, the assistance of air traf-fic control (ATC) may be very useful if a pilot becomeslost. However, in an emergency situation when actionneeds be taken quickly, time may not be available tocontact ATC immediately.

INTERNAL RESOURCESInternal resources are found in the cockpit duringflight. Since some of the most valuable internalresources are ingenuity, knowledge, and skill, a pilotcan expand cockpit resources immensely by improvingthese capabilities. This can be accomplished by fre-quently reviewing flight information publications, suchas the CFRs and the Aeronautical Information Manual(AIM), as well as by pursuing additional training.

A thorough understanding of all the equipment and sys-tems in the airplane is necessary to fully utilize allresources. For example, advanced navigation andautopilot systems are valuable resources. However, ifpilots do not fully understand how to use this equipment,

Anti-Authority — Although he knows that flying so low to the ground is prohibited by the regulations, he feels that the regulations are too restrictive in some circumstances.

Impulsivity — As he is buzzing the park, the airplane does not climb as well as Steve had anticipated and without thinking, Steve pulls back hard on the yoke. The airspeed drops and the airplane is close to a stalling attitude as the wing brushes a power line.

Invulnerability — Steve is not worried about an accident since he has flown this low many times before and he has not had any problems.

Macho — Steve often brags to his friends about his skills as a pilot and how close to the ground he flies. During a local pleasure flight in his single-engine airplane, he decides to buzz some friends barbecuing at a nearby park.

Resignation — Although Steve manages to recover, the wing sustains minor damage. Steve thinks to himself, "It's dangerous for the power company to put those lines so close to a park. If somebody finds out about this I'm going to be in trouble, but it seems like no matter what I do, somebody's always going to criticize."

Follow the rules. They are usually right.

Not so fast. Think first.

It could happen to me.

Taking chances is foolish.

I'm not helpless. I can make a difference.

HAZARDOUS ATTITUDES ANTIDOTES

Figure 16-7. The pilot must be able to identify hazardous atti-tudes and apply the appropriate antidote when needed.

Figure 16-8.The three types of stressors that can affect a pilot’s performance.

STRESSORS

Physical Stress—Conditions associated with the environment, such as temperature and humidity extremes, noise, vibration, and lack of oxygen.

Physiological Stress—Physical conditions, such as fatigue, lack of physical fitness, sleep loss, missed meals (leading to low blood sugar levels), and illness.

Psychological Stress—Social or emotional factors, such as a death in the family, a divorce, a sick child, or a demotion at work. This type of stress may also be related to mental workload, such as analyzing a problem, navigating an aircraft, or making decisions.

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or they rely on it so much that they become complacent,it can become a detriment to safe flight.

Checklists are essential cockpit resources for verifyingthat the airplane instruments and systems are checked,set, and operating properly, as well as ensuring that theproper procedures are performed if there is a systemmalfunction or in-flight emergency. In addition, theAirplane Flight Manual/Pilot’s Operating Handbook(AFM/POH), which is required to be carried on boardthe airplane, is essential for accurate flight planningand for resolving in-flight equipment malfunctions.Other valuable cockpit resources include current aero-nautical charts and publications, such as theAirport/Facility Directory.

Passengers can also be a valuable resource. Passengerscan help watch for traffic and may be able to provideinformation in an irregular situation, especially if theyare familiar with flying. A strange smell or sound mayalert a passenger to a potential problem. A pilot in com-mand should brief passengers before the flight to makesure that they are comfortable voicing any concerns.

EXTERNAL RESOURCESPossibly the greatest external resources during flightare air traffic controllers and flight service specialists.ATC can help decrease pilot workload by providingtraffic advisories, radar vectors, and assistance in emer-gency situations. Flight service stations can provideupdates on weather, answer questions about airportconditions, and may offer direction-finding assistance.The services provided by ATC can be invaluable inenabling a pilot to make informed in-flight decisions.

WORKLOAD MANAGEMENTEffective workload management ensures that essentialoperations are accomplished by planning, prioritizing, andsequencing tasks to avoid work overload. As experience isgained, a pilot learns to recognize future workloadrequirements and can prepare for high workload periodsduring times of low workload. Reviewing the appropriatechart and setting radio frequencies well in advance ofwhen they are needed helps reduce workload as the flightnears the airport. In addition, a pilot should listen to ATIS,ASOS, or AWOS, if available, and then monitor the towerfrequency or CTAF to get a good idea of what traffic con-ditions to expect. Checklists should be performed well inadvance so there is time to focus on traffic and ATCinstructions. These procedures are especially importantprior to entering a high-density traffic area, such as ClassB airspace.

To manage workload, items should be prioritized.During any situation, and especially in an emergency,remember the phrase “aviate, navigate, and communi-cate.” This means that the first thing the pilot should dois to make sure the airplane is under control. Thenbegin flying to an acceptable landing area. Only after

the first two items are assured should the pilot try tocommunicate with anyone.

Another important part of managing workload isrecognizing a work overload situation. The firsteffect of high workload is that the pilot begins towork faster. As workload increases, attention cannotbe devoted to several tasks at one time, and the pilotmay begin to focus on one item. When a pilotbecomes task saturated, there is no awareness ofinputs from various sources, so decisions may bemade on incomplete information, and the possibilityof error increases. [Figure 16-9]

When becoming overloaded, stop, think, slow down,and prioritize. It is important to understand options thatmay be available to decrease workload. For example,tasks such as locating an item on a chart or setting aradio frequency may be delegated to another pilot orpassenger; an autopilot, if available, may be used; orATC may be enlisted to provide assistance.

SITUATIONAL AWARENESSSituational awareness is the accurate perception of theoperational and environmental factors that affect the air-plane, pilot, and passengers during a specific period oftime. Maintaining situational awareness requires anunderstanding of the relative significance of these factorsand their future impact on the flight. When situationallyaware, the pilot has an overview of the total operationand is not fixated on one perceived significant factor.Some of the elements inside the airplane to be consideredare the status of airplane systems, and also the pilot andpassengers. In addition, an awareness of the environmen-tal conditions of the flight, such as spatial orientation ofthe airplane, and its relationship to terrain, traffic,weather, and airspace must be maintained.

To maintain situational awareness, all of the skillsinvolved in aeronautical decision making are used. For

Margin of Safety

Pilot Capabilities

Task Requirements

Preflight Takeoff Cruise Approach & Landing

Taxi TaxiTime

Figure 16-9. Accidents often occur when flying taskrequirements exceed pilot capabilities. The differencebetween these two factors is called the margin of safety.Note that in this idealized example, the margin of safety isminimal during the approach and landing. At this point, anemergency or distraction could overtax pilot capabilities,causing an accident.

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example, an accurate perception of pilot fitness can beachieved through self-assessment and recognition ofhazardous attitudes. A clear assessment of the status ofnavigation equipment can be obtained throughworkload management, and establishing a produc-tive relationship with ATC can be accomplished byeffective resource use.

OBSTACLES TO MAINTAINING SITUATIONALAWARENESSFatigue, stress, and work overload can cause a pilot tofixate on a single perceived important item rather thanmaintaining an overall awareness of the flight situation.A contributing factor in many accidents is a distractionthat diverts the pilot’s attention from monitoring theinstruments or scanning outside the airplane. Manycockpit distractions begin as a minor problem, such as agauge that is not reading correctly, but result in accidentsas the pilot diverts attention to the perceived problemand neglects to properly control the airplane.

Complacency presents another obstacle to maintainingsituational awareness. When activities become routine,there is a tendency to relax and not put as much effort intoperformance. Like fatigue, complacency reduces a pilot’seffectiveness in the cockpit. However, complacency isharder to recognize than fatigue, since everything is per-

ceived to be progressing smoothly. For example, a pilothas not bothered to calculate the CG of the airplanebecause it has never been a problem. Without the pilotrealizing it, a passenger loads a heavy piece of equipmentin the nose baggage compartment. The pilot notices severenose heaviness during climb-out after takeoff, and finds itnecessary to use full nose-up trim to maintain level flight.As the pilot flares for landing, the elevator reaches the stopwithout raising the nose enough, and the nose-first land-ing results in loss of the nose gear and extensive damageto the airplane.

OPERATIONAL PITFALLSThere are a number of classic behavioral traps into whichpilots have been known to fall. Pilots, particularly thosewith considerable experience, as a rule, always try tocomplete a flight as planned, please passengers, andmeet schedules. The basic drive to meet or exceed goalscan have an adverse effect on safety, and can impose anunrealistic assessment of piloting skills under stressfulconditions. These tendencies ultimately may bring aboutpractices that are dangerous and often illegal, and maylead to a mishap. A pilot will develop awareness andlearn to avoid many of these operational pitfalls througheffective ADM training. [Figure 16-10]

Peer Pressure—Poor decision making may be based upon an emotional response to peers, rather than evaluating a situation objectively.

Mind Set—A pilot displays mind set through an inability to recognize and cope with changes in a given situation.

Get-There-Itis—This disposition impairs pilot judgment through a fixation on the original goal or destination, combined with a disregard for any alternative course of action.

Duck-Under Syndrome—A pilot may be tempted to make it into an airport by descending below minimums during an approach. There may be a belief that there is a built-in margin of error in every approach procedure, or a pilot may want to admit that the landing cannot be completed and a missed approach must be initiated.

Scud Running—This occurs when a pilot tries to maintain visual contact with the terrain at low altitudes while instrument conditions exist.

Continuing Visual Flight Rules (VFR) into Instrument Conditions—Spatial disorientation or collision with ground/obstacles may occur when a pilot continues VFR into instrument conditions. This can be even more dangerous if the pilot is not instrument-rated or current.

Getting Behind the Aircraft —This pitfall can be caused by allowing events or the situation to control pilot actions. A constant state of surprise at what happens next may be exhibited when the pilot is getting behind the aircraft.

Loss of Positional or Situational Awareness—In extreme cases, when a pilot gets behind the aircraft, a loss of positional or situational awareness may result. The pilot may not know the aircraft's geographical location, or may be unable to recognize deteriorating circumstances.

Operating Without Adequate Fuel Reserves—Ignoring minimum fuel reserve requirements is generally the result of overconfidence, lack of flight planning, or disregarding applicable regulations.

Descent Below the Minimum En Route Altitude—The duck-under syndrome, as mentioned above, can also occur during the en route portion of an IFR flight.

Flying Outside the Envelope—The assumed high performance capability of a particular aircraft may cause a mistaken belief that it can meet the demands imposed by a pilot's overestimated flying skills.

Neglect of Flight Planning, Preflight Inspections, and Checklists—A pilot may rely on short- and long-term memory, regular flying skills, and familiar routes instead of established procedures and published checklists. This can be particularly true of experienced pilots.

OPERATIONAL PITFALLS

Figure 16-10. All experienced pilots have fallen prey to, or have been tempted by, one or more of these tendencies in their flyingcareers.

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100-HOUR INSPECTION — Aninspection, identical in scope to anannual inspection. Conducted every100 hours of flight on aircraft of under12,500 pounds that are used to carrypassengers for hire.

ABSOLUTE ALTITUDE—The ver-tical distance of an airplane above theterrain, or above ground level (AGL).

ACCELERATION—Force involvedin overcoming inertia, and which maybe defined as a change in velocity perunit of time.

ACCELERATION ERROR —Fluctuation of the magnetic compassduring acceleration. In the NorthernHemisphere, the compass swingstoward the north during acceleration.

ACCELERATE-GODISTANCE — The distancerequired to accelerate to V1 with allengines at takeoff power, experiencean engine failure at V1 and continuethe takeoff on the remainingengine(s). The runway requiredincludes the distance required toclimb to 35 feet by which time V2speed must be attained.

ACCELERATE-STOPDISTANCE — The distancerequired to accelerate to V1 with allengines at takeoff power, experiencean engine failure at V1, and abort thetakeoff and bring the airplane to astop using braking action only (useof thrust reversing is not consid-ered).

ADF—See AUTOMATIC DIREC-TION FINDER.

ADIABATIC COOLING — Aprocess of cooling the air throughexpansion. For example, as air moves

graphic features, hazards and obstruc-tions, navigation aids, navigationroutes, designated airspace, and air-ports.

AERONAUTICAL DECISIONMAKING (ADM)—A systematicapproach to the mental process usedby pilots to consistently determine thebest course of action in response to agiven set of circumstances.

AGONIC LINE—Line along whichthe variation between true and mag-netic values is zero.

AILERONS—Primary flight controlsurfaces mounted on the trailing edgeof an airplane wing, near the tip.Ailerons control roll about the longi-tudinal axis.

AIRCRAFT — A device that is used,or intended to be used, for flight.

AIRCRAFT ALTITUDE—Theactual height above sea level at whichthe aircraft is flying.

AIRFOIL—Any surface, such as awing, propeller, rudder, or even a trimtab, which provides aerodynamicforce when it interacts with a movingstream of air.

AIR MASS—An extensive body ofair having fairly uniform properties oftemperature and moisture.

AIRMET—In-flight weather advisoryconcerning moderate icing, moderateturbulence, sustained winds of 30 knotsor more at the surface, and widespreadareas of ceilings less than 1,000 feetand/or visibility less than 3 miles.

AIRPLANE—An engine-driven,fixed-wing aircraft heavier than airthat is supported in flight by thedynamic reaction of air against itswings.

up slope it expands with the reductionof atmospheric pressure and cools asit expands.

ADIABATIC HEATING — Aprocess of heating dry air throughcompression. For example, as airmoves down a slope it is compressed,which results in an increase in temper-ature.

ADJUSTABLE-PITCHPROPELLER—A propeller withblades whose pitch can be adjusted onthe ground with the engine not run-ning, but which cannot be adjusted inflight. Also referred to as a groundadjustable propeller. Sometimes alsoused to refer to constant-speed pro-pellers that are adjustable in flight.

ADJUSTABLE STABILIZER—Astabilizer that can be adjusted in flightto trim the airplane, thereby allowingthe airplane to fly hands-off at anygiven airspeed.

ADVECTION FOG—Fog resultingfrom the movement of warm, humidair over a cold surface.

ADVERSE YAW—A condition offlight in which the nose of an airplanetends to yaw toward the outside of theturn. This is caused by the higherinduced drag on the outside wing,which is also producing more lift.Induced drag is a by-product of the liftassociated with the outside wing.

AERODYNAMICS—The science ofthe action of air on an object, and withthe motion of air on other gases.Aerodynamics deals with the produc-tion of lift by the aircraft, the relativewind, and the atmosphere.

AERONAUTICAL CHART — Amap used in air navigation containingall or part of the following: topo-

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AIRPLANE FLIGHT MANUAL(AFM)—A document developed bythe airplane manufacturer andapproved by the Federal AviationAdministration (FAA). It is specific toa particular make and model airplaneby serial number and it contains oper-ating procedures and limitations.

AIRPLANE OWNER/INFORMATION MANUAL — Adocument developed by the airplanemanufacturer containing generalinformation about the make andmodel of an airplane. The airplaneowner’s manual is not FAA-approved and is not specific to aparticular serial numbered airplane.This manual is not kept current, andtherefore cannot be substituted forthe AFM/POH.

AIRPORT ADVISORY AREA—Anarea within 10 statute miles (SM) ofan airport where a control tower is notoperating, but where a flight servicestation (FSS) is located. At theselocations, the FSS provides advisoryservice to arriving and departing air-craft.

AIRPORT/FACILITYDIRECTORY — A publicationdesigned primarily as a pilot’s opera-tional manual containing all airports,seaplane bases, and heliports open tothe public including communicationsdata, navigational facilities, and cer-tain special notices and procedures.This publication is issued in sevenvolumes according to geographicalarea.

AIRSPEED—Rate of the aircraft’sprogress through the air.

AIRSPEED INDICATOR — Aninstrument that is a sensitive, differen-tial pressure gauge which measuresand shows promptly the differencebetween pitot or impact pressure, andstatic pressure, the undisturbed atmos-pheric pressure at level flight.

AIRWORTHINESSCERTIFICATE — A certificateissued by the FAA to all aircraft thathave been proven to meet the mini-mum standards set down by the Codeof Federal Regulations.

ANNUAL INSPECTION—A com-plete inspection of an aircraft andengine, required by the Code ofFederal Regulations, to be accom-plished every 12 calendar months onall certificated aircraft. Only an A&Ptechnician holding an InspectionAuthorization can conduct an annualinspection.

ANTISERVO TAB—An adjustabletab attached to the trailing edge of astabilator that moves in the samedirection as the primary control. It isused to make the stabilator less sensi-tive.

AREA FORECAST (FA)—A reportthat gives a picture of clouds, generalweather conditions, and visual mete-orological conditions (VMC)expected over a large area encompass-ing several states.

AREA NAVIGATION (RNAV)—Asystem that provides enhanced navi-gational capability to the pilot.RNAV equipment can compute theairplane position, actual track andgroundspeed and then providemeaningful information relative to aroute of flight selected by the pilot.Typical equipment will provide thepilot with distance, time, bearingand crosstrack error relative to theselected “TO” or “active” waypointand the selected route. Severaldistinctly different navigationalsystems with different navigationalperformance characteristics are capa-ble of providing area navigationalfunctions. Present day RNAVincludes INS, LORAN, VOR/DME,and GPS systems.

ARM—The horizontal distance ininches from the reference datum lineto the center of gravity of an item. Thealgebraic sign is plus (+) if measuredaft of the datum, and minus (-) ifmeasured forward of the datum.

ASPECT RATIO—Span of a wingdivided by its average chord.

ASYMMETRIC THRUST—Alsoknown as P-factor. A tendency for anaircraft to yaw to the left due to thedescending propeller blade on theright producing more thrust than the

AIRWORTHINESS DIRECTIVE—A regulatory noticesent out by the FAA to the registeredowner of an aircraft informing theowner of a condition that prevents theaircraft from continuing to meetits conditions for airworthiness.Airworthiness Directives (AD notes)are to be complied with within therequired time limit, and the fact ofcompliance, the date of compliance,and the method of compliance arerecorded in the aircraft’s maintenancerecords.

ALERT AREAS—Areas depicted onaeronautical charts to advise pilotsthat a high volume of pilot training orunusual aerial activity is taking place.

ALTIMETER—A flight instrumentthat indicates altitude by sensing pres-sure changes.

ALTITUDE ENGINE—A recipro-cating aircraft engine having a ratedtakeoff power that is produciblefrom sea level to an establishedhigher altitude.

AMBIENT PRESSURE—Thepressure in the area immediatelysurrounding the aircraft.

AMBIENT TEMPERATURE—Thetemperature in the area immediatelysurrounding the aircraft.

ANEROID—A sealed flexible con-tainer that expands or contracts inrelation to the surrounding air pres-sure. It is used in an altimeter or abarometer to measure the pressure ofthe air.

ANGLE OF ATTACK—The acuteangle between the chord line of theairfoil and the direction of the relativewind. It is important in the productionof lift.

ANGLE OF INCIDENCE—Theangle formed by the chord line of thewing and a line parallel to the longitu-dinal axis of the airplane.

ANHEDRAL—A downward slantfrom root to tip of an aircraft’s wingor horizontal tail surface.

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ascending blade on the left. Thisoccurs when the aircraft’s longitudi-nal axis is in a climbing attitude inrelation to the relative wind. The P-factor would be to the right if the air-craft had a counterclockwise rotatingpropeller.

ATTITUDE—A personal motiva-tional predisposition to respond topersons, situations, or events in agiven manner that can, nevertheless,be changed or modified through train-ing as sort of a mental shortcut todecision making.

ATTITUDE INDICATOR — Aninstrument that uses an artificial hori-zon and miniature airplane to depictthe position of the airplane in relationto the true horizon. The attitude indi-cator senses roll as well as pitch,which is the up and down movementof the airplane’s nose.

ATTITUDE MANAGEMENT—The ability to recognize hazardousattitudes in oneself and the willing-ness to modify them as necessarythrough the application of an appro-priate antidote thought.

AUTOKINESIS—This is caused bystaring at a single point of lightagainst a dark background for morethan a few seconds. After a fewmoments, the light appears to moveon its own.

AUTOMATED SURFACEOBSERVATION SYSTEM(ASOS)Weather reporting systemwhich provides surface observationsevery minute via digitized voicebroadcasts and printed reports.

AUTOMATED WEATHEROBSERVING SYSTEM(AWOS) Automated weatherreporting system consisting of varioussensors, a processor, a computer-generated voice subsystem, and atransmitter to broadcast weatherdata.

AUTOMATIC DIRECTIONFINDER (ADF)—An aircraft radionavigation system which senses andindicates the direction to an L/MFnondirectional radio beacon (NDB)ground transmitter. Direction is

surface, which automatically movesin the direction opposite the primarycontrol to provide an aerodynamicassist in the movement of the control.Sometimes referred to as a servo tab.

BASIC EMPTY WEIGHT(GAMA)—Basic empty weightincludes the standard empty weightplus optional and special equipmentthat has been installed.

BERNOULLI’S PRINCIPLE—Aprinciple that explains how the pres-sure of a moving fluid varies with itsspeed of motion. An increase in thespeed of movement causes a decreasein the fluid’s pressure.

BIPLANES—Airplanes with twosets of wings.

BYPASS RATIO—The ratio of themass airflow in pounds per secondthrough the fan section of a turbofanengine to the mass airflow that passesthrough the gas generator portion ofthe engine.

CABIN ALTITUDE—Cabin pres-sure in terms of equivalent altitudeabove sea level.

CALIBRATED AIRSPEED(CAS)—Indicated airspeed correctedfor installation error and instrumenterror. Although manufacturers attemptto keep airspeed errors to a minimum,it is not possible to eliminate all errorsthroughout the airspeed operatingrange. At certain airspeeds and withcertain flap settings, the installationand instrument errors may total sev-eral knots. This error is generallygreatest at low airspeeds. In the cruis-ing and higher airspeed ranges, indi-cated airspeed and calibrated airspeedare approximately the same. Refer tothe airspeed calibration chart to cor-rect for possible airspeed errors.

CAMBER—The camber of an airfoilis the characteristic curve of its upperand lower surfaces. The upper camberis more pronounced, while the lowercamber is comparatively flat. Thiscauses the velocity of the airflowimmediately above the wing to bemuch higher than that below the wing.

indicated to the pilot as a magneticbearing or as a relative bearing tothe longitudinal axis of the aircraftdepending on the type of indicatorinstalled in the aircraft. In certainapplications, such as military, ADFoperations may be based on airborneand ground transmitters in theVHF/UHF frequency spectrum.

AUTOMATIC TERMINALINFORMATION SERVICE(ATIS)—The continuous broadcast ofrecorded noncontrol information inselected terminal areas. Its purpose isto improve controller effectivenessand to relieve frequency congestionby automating the repetitive transmis-sion of essential but routine informa-tion.

AUTOPILOT—An automatic flightcontrol system which keeps an aircraftin level flight or on a set course.Automatic pilots can be directed bythe pilot, or they may be coupled to aradio navigation signal.

AVIATION ROUTINE WEATHERREPORT (METAR)—Observationof current surface weather reported ina standard international format.

AXES OF AN AIRCRAFT—Threeimaginary lines that pass through anaircraft’s center of gravity. The axescan be considered as imaginary axlesaround which the aircraft turns. Thethree axes pass through the center ofgravity at 90° angles to each other.The axis from nose to tail is the longi-tudinal axis, the axis that passes fromwingtip to wingtip is the lateral axisand the axis that passes verticallythrough the center of gravity is thevertical axis.

AXIAL FLOWCOMPRESSORA type of com-pressor used in a turbine engine inwhich the airflow through thecompressor is essentially linear.An axial-flow compressor is madeup of several stages of alternaterotors and stators. The compressorratio is determined by the decreasein area of the succeeding stages.

BALANCE TAB—An auxiliarycontrol mounted on a primary control

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CANARD—A horizontal surfacemounted ahead of the main wing toprovide longitudinal stability and con-trol. It may be a fixed, movable, orvariable geometry surface, with orwithout control surfaces.

CANARD CONFIGURATION—Aconfiguration in which the span of theforward wings is substantially lessthan that of the main wing.

CANTILEVER—A wing designedto carry the loads without externalstruts.

CEILING—The height above theearth’s surface of the lowest layer ofclouds, which is reported as broken orovercast, or the vertical visibility intoan obscuration.

CENTER OF GRAVITY (CG)—The point at which an airplane wouldbalance if it were possible to suspendit at that point. It is the mass center ofthe airplane, or the theoretical point atwhich the entire weight of the airplaneis assumed to be concentrated. It maybe expressed in inches from the refer-ence datum, or in percent of meanaerodynamic chord (MAC). Thelocation depends on the distributionof weight in the airplane.

CENTER-OF-GRAVITYLIMITS—The specified forward andaft points within which the CG mustbe located during flight. These limitsare indicated on pertinent airplanespecifications.

CENTER-OF-GRAVITYRANGE—The distance between theforward and aft CG limits indicated onpertinent airplane specifications.

CENTER OF PRESSURE—A pointalong the wing chord line where lift isconsidered to be concentrated. Forthis reason, the center of pressure iscommonly referred to as the center oflift.

CENTRIFUGAL FLOW COMPRESSORAn impellershaped device that receives air at itscenter and slings the air outward athigh velocity into a diffuser forincreased pressure. Also referred to asa radial outflow compressor.

CONSTANT-SPEEDPROPELLER—A controllable-pitchpropeller whose pitch is automaticallyvaried in flight by a governor to main-tain a constant r.p.m. in spite of vary-ing air loads.

CONTINUOUS FLOW OXYGENSYSTEM—System that supplies aconstant supply of pure oxygen to arebreather bag that dilutes the pureoxygen with exhaled gases and thussupplies a healthy mix of oxygen andambient air to the mask. Primarilyused in passenger cabins of commer-cial airliners.

CONTROLLABILITY—A measureof the response of an aircraft relativeto the pilot’s flight control inputs.

CONTROLLED AIRPORT—Anairport that has an operating controltower.

CONTROLLED AIRSPACE—Ageneric term that covers the differentclassifications of airspace and defineddimensions within which air trafficcontrol service is provided in accor-dance with the airspace classification.Controlled airspace consists of ClassA, B, C, D, and E airspace.

CONVECTIVESIGMET—A weather advisoryconcerning convective weather sig-nificant to the safety of all aircraft.Convective SIGMETs are issued fortornadoes, lines of thunderstorms,thunderstorms over a wide area,embedded thunderstorms, windgusts to 50 knots or greater, and/orhail 3/4 inch in diameter or greater.

CONVENTIONALLANDING GEAR—Landing gearemploying a third rear-mountedwheel. These airplanes are alsosometimes referred to as tailwheelairplanes.

COUPLED AILERONS ANDRUDDER—Rudder and ailerons areconnected with interconnect springsin order to counteract adverse yaw.Can be overridden if it becomes nec-essary to slip the aircraft.

COURSE—The intended directionof flight in the horizontal plane meas-ured in degrees from north.

CENTRIFUGAL FORCE — Anoutward force, that opposes cen-tripetal force, resulting from theeffect of inertia during a turn.

CENTRIPETAL FORCE—A cen-ter-seeking force directed inwardtoward the center of rotation createdby the horizontal component of lift inturning flight.

CHORD LINE—An imaginarystraight line drawn through an airfoilfrom the leading edge to the trailingedge.

COEFFICIENT OF LIFT—Theratio between lift pressure anddynamic pressure.

COLD FRONT—The boundarybetween two air masses where cold airis replacing warm air.

COMPLEX AIRCRAFT—Anaircraft with retractable landinggear, flaps, and a controllable-pitch propeller.

COMPRESSORPRESSURE RATIO—The ratio ofcompressor discharge pressure tocompressor inlet pressure.

COMPRESSOR STALL—In gasturbine engines, a condition in anaxial-flow compressor in which oneor more stages of rotor blades fail topass air smoothly to the succeedingstages. A stall condition is caused by apressure ratio that is incompatiblewith the engine r.p.m. Compressorstall will be indicated by a rise inexhaust temperature or r.p.m. fluctua-tion, and if allowed to continue, mayresult in flameout and physical dam-age to the engine.

CONDENSATIONA change ofstate of water from a gas (water vapor)to a liquid.

CONDENSATIONNUCLEI—Small particles of solidmatter in the air on which water vaporcondenses.

CONFIGURATION—This is a gen-eral term, which normally refers to theposition of the landing gear and flaps.

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COWL FLAPS — Shutter-likedevices arranged around certainair-cooled engine cowlings, whichmay be opened or closed to regulatethe flow of air around the engine.

CREW RESOURCE MANAGE-MENT (CRM)—The application ofteam management concepts in theflight deck environment. It wasinitially known as cockpit resourcemanagement, but as CRM programsevolved to include cabin crews,maintenance personnel, and others,the phrase “crew resource manage-ment” was adopted. This includessingle pilots, as in most generalaviation aircraft. Pilots of smallaircraft, as well as crews of largeraircraft, must make effective use of allavailable resources; human resources,hardware, and information. A currentdefinition includes all groupsroutinely working with the cockpitcrew who are involved in decisionsrequired to operate a flight safely.These groups include, but are notlimited to: pilots, dispatchers, cabincrewmembers, maintenance person-nel, and air traffic controllers. CRM isone way of addressing the challengeof optimizing the human/machineinterface and accompanying interper-sonal activities.

CRITICAL ALTITUDE — Themaximum altitude under standardatmospheric conditions at which aturbocharged engine can produce itsrated horsepower.

CRITICAL ANGLE OFATTACK—The angle of attack atwhich a wing stalls regardless ofairspeed, flight attitude, or weight.

DATUM (REFERENCEDATUM)—An imaginary verticalplane or line from which all measure-ments of arm are taken. The datum isestablished by the manufacturer. Oncethe datum has been selected, allmoment arms and the location of CGrange are measured from this point.

DEAD RECKONING—Navigationof an airplane solely by means ofcomputations based on airspeed,

DIFFERENTIAL AILERONS —Control surface rigged such that theaileron moving up moves a greaterdistance than the aileron movingdown. The up aileron produces extraparasite drag to compensate for theadditional induced drag caused by thedown aileron. This balancing of thedrag forces helps minimize adverseyaw.

DIFFERENTIAL PRESSURE—Adifference between two pressures. Themeasurement of airspeed is an exam-ple of the use of differential pressure.

DIHEDRAL—The positive acuteangle between the lateral axis of anairplane and a line through the centerof a wing or horizontal stabilizer.Dihedral contributes to the lateralstability of an airplane.

DILUTER-DEMAND OXYGENSYSTEM—An oxygen system thatdelivers oxygen mixed or diluted withair in order to maintain a constantoxygen partial pressure as the altitudechanges.

DIRECT USER ACCESS TERMI-NAL SERVICE (DUATS)—A com-puter-based program providing NWSand FAA weather products that arenormally used in pilot weatherbriefings.

DIRECTIONAL STABILITY—Stability about the vertical axis of anaircraft, whereby an aircraft tends toreturn, on its own, to flight alignedwith the relative wind when disturbedfrom that equilibrium state. The verti-cal tail is the primary contributor todirectional stability, causing anairplane in flight to align with therelative wind.

DISTANCE MEASURING EQUIP-MENT (DME)—Equipment (air-borne and ground) to measure, innautical miles, the slant range distanceof an aircraft from the DME naviga-tion aid.

DRAG—An aerodynamic force on abody acting parallel and opposite tothe relative wind. The resistance ofthe atmosphere to the relative motionof an aircraft. Drag opposes thrust andlimits the speed of the airplane.

course, heading, wind direction, andspeed, groundspeed, and elapsed time.

DECELERATIONERROR—Fluctuation of the mag-netic compass during acceleration.In the Northern Hemisphere, thecompass swings toward the southduring deceleration.

DELTA—A Greek letter expressed bythe symbol ∆ to indicate a change ofvalues. As an example, ∆CG indicatesa change (or movement) of the CG.

DENSITY ALTITUDE—This alti-tude is pressure altitude corrected forvariations from standard temperature.When conditions are standard, pressurealtitude and density altitude are thesame. If the temperature is above stan-dard, the density altitude is higher thanpressure altitude. If the temperature isbelow standard, the density altitude islower than pressure altitude. This is animportant altitude because it is directlyrelated to the airplane’s performance.

DEPOSITIONThe direct transfor-mation of a gas to a solid state, in whichthe liquid state is bypassed. Somesources use sublimation to describe thisprocess instead of deposition.

DETONATION — The suddenrelease of heat energy from fuel inan aircraft engine caused by thefuel-air mixture reaching its criticalpressure and temperature. Detonationoccurs as a violent explosion ratherthan a smooth burning process.

DEVIATION — A compass errorcaused by magnetic disturbances fromelectrical and metal components in theairplane. The correction for this erroris displayed on a compass correctioncard placed near the magnetic com-pass in the airplane.

DEW—Moisture that has condensedfrom water vapor. Usually found oncooler objects near the ground, suchas grass, as the near-surface layer ofair cools faster than the layers of airabove it.

DEWPOINT—The temperature atwhich air reaches a state where it canhold no more water.

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DRIFT ANGLE—Angle betweenheading and track.

DUATS — See DIRECT USERACCESS TERMINAL SERVICE.

DUTCH ROLL—A combination ofrolling and yawing oscillations thatnormally occurs when the dihedraleffects of an aircraft are more power-ful than the directional stability.Usually dynamically stable butobjectionable in an airplane becauseof the oscillatory nature.

DYNAMIC HYDROPLANING—Acondition that exists when landing ona surface with standing water deeperthan the tread depth of the tires. Whenthe brakes are applied, there is a pos-sibility that the brake will lock up andthe tire will ride on the surface of thewater, much like a water ski. Whenthe tires are hydroplaning, directionalcontrol and braking action are virtu-ally impossible. An effective anti-skidsystem can minimize the effects ofhydroplaning.

DYNAMIC STABILITY — Theproperty of an aircraft that causes it,when disturbed from straight-and-level flight, to develop forces ormoments that restore the original con-dition of straight and level.

EDDY CURRENT DAMPING—The decreased amplitude of oscilla-tions by the interaction of magneticfields. In the case of a vertical cardmagnetic compass, flux from theoscillating permanent magnet pro-duces eddy currents in a damping diskor cup. The magnetic flux producedby the eddy currents opposes the fluxfrom the permanent magnet anddecreases the oscillations.

ELEVATOR—The horizontal, mov-able primary control surface in the tailsection, or empennage, of an airplane.The elevator is hinged to the trailingedge of the fixed horizontal stabilizer.

EMPENNAGE—The section of theairplane that consists of the verticalstabilizer, the horizontal stabilizer,and the associated control surfaces.

EMPTY-FIELD MYOPIA—Induced nearsightedness that is

Fixed-pitch propellers are designed asclimb propellers, cruise propellers, orstandard propellers.

FIXED SLOT—A fixed, nozzle-shaped opening near the leading edgeof a wing that ducts air onto the topsurface of the wing. Its purpose is toincrease lift at higher angles of attack.

FLAMEOUT—A condition in theoperation of a gas turbine engine inwhich the fire in the engine goes outdue to either too much or too little fuelsprayed into the combustors.

FLAPS—Hinged portion of the trail-ing edge between the ailerons andfuselage. In some aircraft aileronsand flaps are interconnected to pro-duce full-span “flaperons.” In eithercase, flaps change the lift and drag onthe wing.

FLOOR LOAD LIMIT—The maxi-mum weight the floor can sustain persquare inch/foot as provided by themanufacturer.

FOG—Cloud consisting of numerousminute water droplets and based at thesurface; droplets are small enough tobe suspended in the earth’s atmos-phere indefinitely. (Unlike drizzle, itdoes not fall to the surface; differsfrom cloud only in that a cloud is notbased at the surface; distinguishedfrom haze by its wetness and graycolor.)

FORCE (F)—The energy applied toan object that attempts to cause theobject to change its direction, speed,or motion. In aerodynamics, it isexpressed as F, T (thrust), L (lift), W(weight), or D (drag), usually inpounds.

FOREIGN OBJECT DAMAGE(FOD)Damage to a gas turbineengine caused by some object beingsucked into the engine while it is run-ning. Debris from runways or taxi-ways can cause foreign object damageduring ground operations, and theingestion of ice and birds can causeFOD in flight.

FRISE-TYPE AILERON—Aileronhaving the nose portion projectingahead of the hinge line. When the

associated with flying at night, ininstrument meteorological condi-tions and/or reduced visibility.With nothing to focus on, the eyesautomatically focus on a point justslightly ahead of the airplane.

ENGINE PRESSURE RATIO(EPR)—The ratio of turbine dis-charge pressure divided by compres-sor inlet pressure, which is used as anindication of the amount of thrustbeing developed by a turbine engine.

EN ROUTE FLIGHT ADVISORYSERVICE (EFAS)—A servicespecifically designed to provide, uponpilot request, timely weather informa-tion pertinent to the type of flight,intended route of flight and altitude.The FSSs providing this service arelisted in the Airport/FacilityDirectory. Also known as FlightWatch.

EQUILIBRIUM—A condition thatexists within a body when the sum ofthe moments of all of the forces actingon the body is equal to zero. In aero-dynamics, equilibrium is when allopposing forces acting on an aircraftare balanced (steady, unacceleratedflight conditions).

EQUIVALENT AIRSPEED—Theairspeed indicator reading correctedfor position (or installation), or instru-ment error, and for adiabatic com-pressible flow for the particularaltitude. (EAS is equal to CAS at sealevel in standard atmosphere.)

EVAPORATION—The transforma-tion of a liquid to a gaseous state, suchas the change of water to water vapor.

EXHAUST GAS TEMPERATURE(EGT)—The temperature of theexhaust gases as they leave the cylin-ders of a reciprocating engine or theturbine section of a turbine engine.

EXPLOSIVEDECOMPRESSION—A change incabin pressure faster than the lungscan decompress. Lung damage is pos-sible.

FIXED-PITCH PROPELLERS—Propellers with fixed blade angles.

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trailing edge of the aileron moves up,the nose projects below the wing’slower surface and produces some par-asite drag, decreasing the amount ofadverse yaw.

FRONT—The boundary betweentwo different air masses.

FROST—Ice crystal deposits formedby sublimation when temperature anddewpoint are below freezing.

FUEL LOAD—The expendable partof the load of the airplane. It includesonly usable fuel, not fuel required tofill the lines or that which remainstrapped in the tank sumps.

FUSELAGE—The section of theairplane that consists of the cabinand/or cockpit, containing seats forthe occupants and the controls for theairplane.

GIMBAL RING—A type of supportthat allows an object, such as a gyro-scope, to remain in an upright condi-tion when its base is tilted.

GPS (GLOBAL POSITIONINGSYSTEM)A satellite-based radiopositioning, navigation, and time-transfer system.

GROUND ADJUSTABLE TRIMTAB—Non-movable metal trim tabon a control surface. Bent in onedirection or another while on theground to apply trim forces to the con-trol surface.

GROUND EFFECT—The conditionof slightly increased air pressurebelow an airplane wing or helicopterrotor system that increases the amountof lift produced. It exists withinapproximately one wing span or onerotor diameter from the ground. Itresults from a reduction in upwash,downwash, and wingtip vortices, andprovides a corresponding decrease ininduced drag.

GROUNDSPEED (GS)—The actualspeed of the airplane over the ground.It is true airspeed adjusted for wind.Groundspeed decreases with a head-wind, and increases with a tailwind.

HORSEPOWER—The term, origi-nated by inventor James Watt, meansthe amount of work a horse could doin one second. One horsepower equals550 foot-pounds per second, or33,000 foot-pounds per minute.

HOT START—In gas turbineengines, a start which occurs withnormal engine rotation, but exhausttemperature exceeds prescribedlimits. This is usually caused by anexcessively rich mixture in thecombustor. The fuel to the enginemust be terminated immediately toprevent engine damage.

HUMAN FACTORS—The study ofhow people interact with their envi-ronments. In the case of general avia-tion, it is the study of how pilotperformance is influenced by suchissues as the design of cockpits, thefunction of the organs of the body, theeffects of emotions, and the interac-tion and communication with theother participants of the aviation com-munity, such as other crewmembersand air traffic control personnel.

HUNG START In gas turbineengines, a condition of normal lightoff but with r.p.m. remaining at somelow value rather than increasing to thenormal idle r.p.m. This is often theresult of insufficient power to theengine from the starter. In the event ofa hung start, the engine should be shutdown.

HYDROPLANING—A conditionthat exists when landing on a sur-face with standing water deeperthan the tread depth of the tires.When the brakes are applied, thereis a possibility that the brake willlock up and the tire will ride on thesurface of the water, much like awater ski. When the tires arehydroplaning, directional controland braking action are virtuallyimpossible. An effective anti-skidsystem can minimize the effects ofhydroplaning.

HYPEMIC HYPOXIA—A type ofhypoxia that is a result of oxygen defi-ciency in the blood, rather than a lackof inhaled oxygen. It can be caused bya variety of factors. Hypemic means“not enough blood.”

GYROSCOPIC PRECESSION—An inherent quality of rotating bodies,which causes an applied force to bemanifested 90º in the direction of rota-tion from the point where the force isapplied.

HAZARDOUS ATTITUDES—These can lead to poor decisionmaking and actions that involveunnecessary risk. Pilots must exam-ine decisions carefully to ensurethey have not been influenced byhazardous attitudes.

HAZARDOUS INFLIGHTWEATHER ADVISORY SERVICE(HIWAS) — Continuous recordedhazardous inflight weather forecastsbroadcasted to airborne pilots overselected VOR outlets defined as anHIWAS Broadcast Area.

HEADING—The direction in whichthe nose of the aircraft is pointing dur-ing flight.

HEADING INDICATOR — Aninstrument which senses airplanemovement and displays headingbased on a 360º azimuth, with thefinal zero omitted. The heading indi-cator, also called a directional gyro(DG), is fundamentally a mechanicalinstrument designed to facilitate theuse of the magnetic compass. Theheading indicator is not affected bythe forces that make the magneticcompass difficult to interpret.

HEADWORK — Required toaccomplish a conscious, rationalthought process when making deci-sions. Good decision makinginvolves risk identification andassessment, information processing,and problem solving.

HIGH PERFORMANCEAIRCRAFT—An aircraft with anengine of more than 200 horsepower.

HISTOTOXIC HYPOXIA — Theinability of the cells to effectively useoxygen. Plenty of oxygen is beingtransported to the cells that need it,but they are unable to make use of it.

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HYPERVENTILATION—Occurswhen an individual is experiencingemotional stress, fright, or pain, andthe breathing rate and depth increase,although the carbon dioxide level inthe blood is already at a reduced level.The result is an excessive loss of car-bon dioxide from the body, which canlead to unconsciousness due to therespiratory system’s overriding mech-anism to regain control of breathing.

HYPOXIA—Hypoxia means“reduced oxygen” or “not enoughoxygen.” Hypoxia can be caused byseveral factors including an insuffi-cient supply of oxygen, inadequatetransportation of oxygen, or theinability of the body tissues to useoxygen.

HYPOXIC HYPOXIA—This typeof hypoxia is a result of insufficientoxygen available to the lungs. Adecrease of oxygen molecules at suf-ficient pressure can lead to hypoxichypoxia.

IFR (INSTRUMENT FLIGHTRULES)Rules that govern theprocedure for conducting flight inweather conditions below VFRweather minimums. The term IFRalso is used to define weather condi-tions and the type of flight planunder which an aircraft is operating.

ILS (INSTRUMENT LANDINGSYSTEM)A precision instrumentapproach system, which normallyconsists of the following electroniccomponents and visual aids—local-izer, glide slope, outer marker, andapproach lights.

INCLINOMETER—An instrumentconsisting of a curved glass tube,housing a glass ball, and damped witha fluid similar to kerosene. It may beused to indicate inclination, as a level,or, as used in the turn indicators, toshow the relationship between gravityand centrifugal force in a turn.

INDICATED AIRSPEED (IAS)—The direct instrument readingobtained from the airspeed indicator,uncorrected for variations in atmos-

JETSTREAM—A narrow band ofwind with speeds of 100 to 200 m.p.h.usually co-located with thetropopause.

JUDGMENT—The mental processof recognizing and analyzing all perti-nent information in a particular situa-tion, a rational evaluation ofalternative actions in response to it,and a timely decision on which actionto take.

LAND BREEZE—A coastal breezeflowing from land to sea caused bytemperature differences when the seasurface is warmer than the adjacentland. The land breeze usually occursat night and alternates with the seabreeze that blows in the oppositedirection by day.

LATERAL AXIS—An imaginaryline passing through the center ofgravity of an airplane and extendingacross the airplane from wingtip towingtip.

LATERAL STABILITY(ROLLING)—The stability about thelongitudinal axis of an aircraft.Rolling stability or the ability of anairplane to return to level flight due toa disturbance that causes one of thewings to drop.

LATITUDE—Measurement north orsouth of the equator in degrees, min-utes, and seconds. Lines of latitude arealso referred to as parallels.

LEADING EDGE—The part of anairfoil that meets the airflow first.

LEADING EDGE DEVICES —High lift devices which are found onthe leading edge of the airfoil. Themost common types are fixed slots,movable slats, and leading edge flaps.

LEADING EDGE FLAP—A por-tion of the leading edge of an airplanewing that folds downward to increasethe camber, lift, and drag of the wing.The leading-edge flaps are extendedfor takeoffs and landings to increasethe amount of aerodynamic lift that isproduced at any given airspeed.

pheric density, installation error, orinstrument error. Manufacturers usethis airspeed as the basis for determin-ing airplane performance. Takeoff,landing, and stall speeds listed in theAFM or POH are indicated airspeedsand do not normally vary with altitudeor temperature.

INDICATED ALTITUDE — Thealtitude read directly from the altime-ter (uncorrected) when it is set to thecurrent altimeter setting.

INDUCED DRAG—That part oftotal drag which is created by the pro-duction of lift. Induced drag increaseswith a decrease in airspeed.

INTERCOOLER—A device used toreduce the temperatures of the com-pressed air before it enters the fuelmetering device. The resulting coolerair has a higher density, which permitsthe engine to be operated with ahigher power setting.

INTERPOLATION—The estima-tion of an intermediate value of aquantity that falls between markedvalues in a series. Example: In a meas-urement of length, with a rule that ismarked in 1/8’s of an inch, the valuefalls between 3/8 inch and 1/2 inch.The estimated (interpolated) valuemight then be said to be 7/16 inch.

INVERSION—An increase in tem-perature with altitude.

ISA (INTERNATIONALSTANDARD ATMOSPHERE)—Standard atmospheric conditions con-sisting of a temperature of 59°F(15°C), and a barometric pressure of29.92 in. Hg. (1013.2 mb) at sea level.ISA values can be calculated for vari-ous altitudes using a standard lapserate of approximately 2ºC per 1,000feet.

ISOBARS—Lines which connectpoints of equal barometric pressure.

ISOGONIC LINES—Lines oncharts that connect points of equalmagnetic variation.

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LICENSED EMPTY WEIGHT—The empty weight that consists of theairframe, engine(s), unusable fuel,and undrainable oil plus standard andoptional equipment as specified in theequipment list. Some manufacturersused this term prior to GAMA stan-dardization.

LIFT—One of the four main forcesacting on an aircraft. On a fixed-wingaircraft, an upward force created bythe effect of airflow as it passes overand under the wing.

LIMIT LOAD FACTOR—Amountof stress, or load factor, that an aircraftcan withstand before structural dam-age or failure occurs.

LOAD FACTOR—The ratio of theload supported by the airplane’s wingsto the actual weight of the aircraft andits contents. Also referred to as G-loading.

LONGITUDE—Measurement eastor west of the Prime Meridian indegrees, minutes, and seconds. ThePrime Meridian is 0° longitude andruns through Greenwich, England.Lines of longitude are also referred toas meridians.

LONGITUDINAL AXIS—Animaginary line through an aircraftfrom nose to tail, passing through itscenter of gravity. The longitudinalaxis is also called the roll axis of theaircraft. Movement of the aileronsrotates an airplane about its longitudi-nal axis.

LONGITUDINAL STABILITY(PITCHING)—Stability about thelateral axis. A desirable characteristicof an airplane whereby it tends toreturn to its trimmed angle of attackafter displacement.

LORAN-C—A radio navigation sys-tem that utilizes master and slave sta-tions transmitting timed pulses. Thetime difference in reception of pulsesfrom several stations establishes ahyperbolic line of position, which canbe identified on a LORAN chart. A fixin position is obtained by utilizing sig-nals from two or more stations.

MAXIMUM RAMP WEIGHT—The total weight of a loaded aircraft,including all fuel. It is greater than thetakeoff weight due to the fuel that willbe burned during the taxi and runupoperations. Ramp weight may also bereferred to as taxi weight.

MAXIMUM TAKEOFFWEIGHT—The maximum allowableweight for takeoff.

MAXIMUM WEIGHT—The maxi-mum authorized weight of the aircraftand all of its equipment as specified inthe Type Certificate Data Sheets(TCDS) for the aircraft.

MAXIMUM ZERO FUELWEIGHT (GAMA)—The maximumweight, exclusive of usable fuel.

MEAN AERODYNAMIC CHORD(MAC)—The average distance fromthe leading edge to the trailing edge ofthe wing.

MERIDIANS—Lines of longitude.

MESOSPHERE—A layer of theatmosphere directly above the strato-sphere.

METAR—See AVIATION ROU-TINE WEATHER REPORT.

MICROBURST—A strong down-draft which normally occurs overhorizontal distances of 1 NM or lessand vertical distances of less than1,000 feet. In spite of its small hori-zontal scale, an intense microburstcould induce windspeeds greaterthan 100 knots and downdrafts asstrong as 6,000 feet per minute.

MILITARY OPERATION AREAS (MOA)—Airspace that con-sists of defined vertical and laterallimits established for the purpose ofseparating certain military trainingactivity from IFR traffic. These aredepicted on aeronautical charts.

MILITARY TRAINING ROUTES(MTR)—Routes developed to allowthe military to conduct low-altitude,high-speed training. These routes areidentified on sectional charts.

MAGNETIC BEARING—Themagnetic course to go direct to anNDB station.

MAGNETIC COMPASS—A devicefor determining direction measuredfrom magnetic north.

MAGNETIC DIP—A vertical attrac-tion between a compass needle andthe magnetic poles. The closer the air-craft is to the pole, the more severe theeffect. In the Northern Hemisphere, aweight is placed on the south-facingend of the compass needle; in theSouthern Hemisphere, a weight isplaced on the north-facing end of thecompass needle to somewhat compen-sate for this effect.

MAGNETO—A self-contained,engine-driven unit that supplies elec-trical current to the spark plugs; com-pletely independent of the airplane’selectrical system. Normally there aretwo magnetos per engine.

MAGNUS EFFECT—Lifting forceproduced when a rotating cylinderproduces a pressure differential. Thisis the same effect that makes a base-ball curve or a golf ball slice.

MANEUVERABILITY—Ability ofan aircraft to change directions alonga flightpath and withstand the stressesimposed upon it.

MANEUVERING SPEED (VA) —The maximum speed where full,abrupt control movement can be usedwithout overstressing the airframe.

MANIFOLD ABSOLUTE PRES-SURE (MAP)—The absolute pres-sure of the fuel/air mixture within theintake manifold, usually indicated ininches of mercury.

MASS—The amount of matter in abody.

MAXIMUM LANDING WEIGHT—The greatest weight thatan airplane normally is allowed tohave at landing.

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MINIMUM DRAG—The point onthe total drag curve where the lift-to-drag ratio is the greatest. At this speed,total drag is minimized.

MINIMUM EQUIPMENT LIST(MEL)—A list developed for largeraircraft that outlines equipment thatcan be inoperative for various types offlight including IFR and icing condi-tions. This list is based on the masterminimum equipment list (MMEL)developed by the FAA and must beapproved by the FAA for use. It is spe-cific to an individual aircraft makeand model.

MOMENT—The product of theweight of an item multiplied by itsarm. Moments are expressed inpound-inches (lb-in). Total moment isthe weight of the airplane multipliedby the distance between the datum andthe CG.

MOMENT ARM—The distancefrom a datum to the applied force.

MOMENT INDEX (OR INDEX)—A moment divided by a constant suchas 100, 1,000, or 10,000. The purposeof using a moment index is to simplifyweight and balance computations ofairplanes where heavy items and longarms result in large, unmanageablenumbers.

MONOCOQUE—A shell-like fuse-lage design in which the stressed outerskin is used to support the majority ofimposed stresses. Monocoque fuse-lage design may include bulkheadsbut not stringers.

MONOPLANES—Airplanes with asingle set of wings.

MOVABLE SLAT—A movable aux-iliary airfoil on the leading edge of awing. It is closed in normal flight butextends at high angles of attack. Thisallows air to continue flowing over thetop of the wing and delays airflowseparation.

N1—Rotational speed of the low pres-sure compressor in a turbine engine.

N2—Rotational speed of the highpressure compressor in a turbineengine.

OCCLUDED FRONT—A frontalocclusion occurs when a fast-movingcold front catches up with a slow-moving warm front. The difference intemperature within each frontal sys-tem is a major factor in determiningwhether a cold or warm front occlu-sion occurs.

OUTSIDE AIR TEMPERATURE(OAT)—The measured or indicatedair temperature (IAT) corrected forcompression and friction heating.Also referred to as true air tempera-ture.

OVERBOOST—A condition inwhich a reciprocating engine hasexceeded the maximum manifoldpressure allowed by the manufacturer.Can cause damage to engine compo-nents.

PARALLELS—Lines of latitude.

PARASITE DRAG—That part oftotal drag created by the form or shapeof airplane parts. Parasite dragincreases with an increase in airspeed.

PAYLOAD (GAMA)—The weightof occupants, cargo, and baggage.

PERSONALITY—The embodimentof personal traits and characteristicsof an individual that are set at a veryearly age and extremely resistant tochange.

P-FACTOR—A tendency for an air-craft to yaw to the left due to thedescending propeller blade on theright producing more thrust than theascending blade on the left. Thisoccurs when the aircraft’s longitudi-nal axis is in a climbing attitude inrelation to the relative wind. The P-factor would be to the right if the air-craft had a counterclockwise rotatingpropeller.

PHUGOID OSCILLATIONS —Long-period oscillations of an aircraftaround its lateral axis. It is a slowchange in pitch accompanied byequally slow changes in airspeed.Angle of attack remains constant, andthe pilot often corrects for phugoidoscillations without even being awareof them.

NACELLE—A streamlined enclo-sure on an aircraft in which anengine is mounted. On multienginepropeller-driven airplanes, thenacelle is normally mounted on theleading edge of the wing.

NATIONAL SECURITY AREAS—Airspace that consists of defined ver-tical and lateral dimensionsestablished at locations where there isa requirement for increased securityand safety of ground facilities.

NDB—See NONDIRECTIONALRADIO BEACON.

NEGATIVE STATICSTABILITY—The initial tendencyof an aircraft to continue away fromthe original state of equilibrium afterbeing disturbed.

NEUTRAL STATIC STABILITY—The initial tendency of an aircraft toremain in a new condition after itsequilibrium has been disturbed.

NONDIRECTIONAL RADIOBEACON (NDB)—An L/MF or UHFradio beacon transmitting nondirec-tional signals whereby the pilot of anaircraft equipped with direction find-ing equipment can determine the bear-ing to or from the radio beacon and“home” on or track to or from the sta-tion. When the radio beacon isinstalled in conjunction with theInstrument Landing System marker, itis normally called a Compass Locator.

NOTICES TO AIRMEN(NOTAM)—A notice containingtime-critical information that is eitherof a temporary nature or is not knownfar enough in advance to permit publi-cation on aeronautical charts or otheroperation publications. This caninclude the establishment, condition,or change in any facility, service, pro-cedure, or hazard in the NationalAirspace System.

OBSTRUCTION LIGHTS—Lightsthat can be found both on and off anairport to identify obstructions.

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PILOTAGE—Navigation by visualreference to landmarks.

PILOT’S OPERATING HAND-BOOK (POH)—A document devel-oped by the airplane manufacturer andcontains the FAA-approved AirplaneFlight Manual (AFM) information.

PILOT WEATHER REPORT(PIREP)A report, generated bypilots, concerning meteorologicalphenomena encountered in flight.

PLANFORM—The shape or form ofa wing as viewed from above. It maybe long and tapered, short and rectan-gular, or various other shapes.

PNEUMATIC—Operation by theuse of compressed air.

POOR JUDGMENT CHAIN—Aseries of mistakes that may lead to anaccident or incident. Two basic princi-ples generally associated with the cre-ation of a poor judgment chain are: (1)One bad decision often leads toanother; and (2) as a string of baddecisions grows, it reduces the num-ber of subsequent alternatives for con-tinued safe flight. ADM is intended tobreak the poor judgment chain beforeit can cause an accident or incident.

POSITIVE STATIC STABILITY—The initial tendency to return to a stateof equilibrium when disturbed fromthat state.

POWER—Implies work rate or unitsof work per unit of time, and as such,it is a function of the speed at whichthe force is developed. The term,power required, is generally associ-ated with reciprocating engines.

POWERPLANT—A completeengine and propeller combinationwith accessories.

PRECESSION—The tilting or turn-ing of a gyro in response to deflectiveforces causing slow drifting and erro-neous indications in gyroscopicinstruments.

PRECIPITATION—Any or allforms of water particles (rain, sleet,hail, or snow), that fall from theatmosphere and reach the surface.

reflected by an object in the path ofthe beam. Range is determined bymeasuring the time it takes (at thespeed of light) for the radio wave togo out to the object and then return tothe receiving antenna. The directionof a detected object from a radar siteis determined by the position of therotating antenna when the reflectedportion of the radio wave is received.

RADAR SUMMARY CHART—Aweather product derived from thenational radar network that graphi-cally displays a summary of radarweather reports.

RADAR WEATHER REPORT(SD)—A report issued by radar stationsat 35 minutes after the hour, and specialreports as needed. Provides informationon the type, intensity, and location ofthe echo tops of the precipitation.

RADIOSONDE—A weather instru-ment that observes and reportsmeteorological conditions from theupper atmosphere. This instrumentis typically carried into the atmos-phere by some form of weatherballoon.

RAM RECOVERY—The increasein thrust as a result of ram air pres-sures and density on the front of theengine caused by air velocity.

RAPID DECOMPRESSION—Thealmost instantaneous loss of cabinpressure in aircraft with a pressurizedcockpit or cabin.

REGION OF REVERSE COM-MAND—Flight regime in whichflight at a higher airspeed requires alower power setting and a lower air-speed requires a higher power settingin order to maintain altitude.

RELATIVE BEARING—An angu-lar relationship between two objectsmeasured in degrees clockwise fromthe twelve o’clock position of the firstobject.

RELATIVE HUMIDITY — Theratio of the existing amount of watervapor in the air at a given temperatureto the maximum amount that couldexist at that temperature; usuallyexpressed in percent.

PREIGNITION—Ignition occurringin the cylinder before the time of nor-mal ignition. Preignition is oftencaused by a local hot spot in the com-bustion chamber igniting the fuel-airmixture.

PRESSURE ALTITUDE—Thealtitude indicated when the altimetersetting window (barometric scale) isadjusted to 29.92. This is the alti-tude above the standard datumplane, which is a theoretical planewhere air pressure (corrected to15ºC) equals 29.92 in. Hg. Pressurealtitude is used to compute densityaltitude, true altitude, true airspeed,and other performance data.

PRESSURE DEMAND OXYGENSYSTEM—A demand oxygen systemthat supplies 100 percent oxygen atsufficient pressure above the altitudewhere normal breathing is adequate.Also referred to as a pressure breathingsystem.

PREVENTIVEMAINTENANCE—Simple or minorpreservative operations and thereplacement of small standard partsnot involving complex assembly oper-ation as listed in Appendix A of 14CFR part 43. Certificated pilots mayperform preventive maintenance onany aircraft that is owned or operatedby them provided that the aircraft isnot used in air carrier service.

PROHIBITED AREAS—Areas thatare established for security or otherreasons associated with the nationalwelfare.

PROPELLER—A device for pro-pelling an aircraft that, when rotated,produces by its action on the air, athrust approximately perpendicular toits plane of rotation. It includes thecontrol components normally sup-plied by its manufacturer.

RADAR SERVICES—Radar is amethod whereby radio waves aretransmitted into the air and are thenreceived when they have been

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RELATIVE WIND—The directionof the airflow with respect to the wing.If a wing moves forward horizontally,the relative wind moves backwardhorizontally. Relative wind is parallelto and opposite the flightpath of theairplane.

RESTRICTED AREAS—Areas thatdenote the existence of unusual, ofteninvisible hazards to aircraft such asartillery firing, aerial gunnery, orguided missiles. An aircraft may notenter a restricted area unless per-mission has been obtained from thecontrolling agency.

RIGGING—The final adjustmentand alignment of an aircraft and itsflight control system that provides theproper aerodynamic characteristics.

RIGIDITY IN SPACE—The princi-ple that a wheel with a heavilyweighted rim spun rapidly will remainin a fixed position in the plane inwhich it is spinning.

RISK ELEMENTS—There are fourfundamental risk elements: the pilot,the aircraft, the environment, and thetype of operation that comprise anygiven aviation situation.

RISK MANAGEMENT—The partof the decision making process whichrelies on situational awareness, prob-lem recognition, and good judgmentto reduce risks associated with eachflight.

RNAV—See AREA NAVIGATION.

RUDDER—The movable primarycontrol surface mounted on thetrailing edge of the vertical fin ofan airplane. Movement of the rud-der rotates the airplane about itsvertical axis.

RUDDERVATOR—A pair of controlsurfaces on the tail of an aircraftarranged in the form of a V. These sur-faces, when moved together by thecontrol wheel, serve as elevators, andwhen moved differentially by the rud-der pedals, serve as a rudder.

RUNWAY CENTERLINELIGHTS—Runway lighting whichconsists of flush centerline lights

SERVO—A motor or other form ofactuator which receives a small signalfrom the control device and exerts alarge force to accomplish the desiredwork.

SERVO TAB—An auxiliary controlmounted on a primary control surface,which automatically moves in thedirection opposite the primary controlto provide an aerodynamic assist inthe movement of the control.

SIGMET—An in-flight weatheradvisory that is considered significantto all aircraft. SIGMET criteriainclude severe icing, severe andextreme turbulence, duststorms, sand-storms, volcanic eruptions, and vol-canic ash that lower visibility to lessthan 3 miles.

SIGNIFICANT WEATHERPROGNOSTIC CHART—Presentsfour panels showing forecast signifi-cant weather and forecast surfaceweather.

SITUATIONAL AWARENESS—The accurate perception and under-standing of all the factors andconditions within the four fundamentalrisk elements that affect safety before,during, and after the flight.

SKILLS AND PROCEDURES—The procedural, psychomotor, andperceptual skills used to control a spe-cific aircraft or its systems. They arethe airmanship abilities that aregained through conventional training,are perfected, and become almostautomatic through experience.

SPATIAL DISORIENTATION—Specifically refers to the lack of ori-entation with regard to the position,attitude, or movement of the airplanein space.

SPECIAL FLIGHT PERMIT—Aflight permit issued to an aircraft thatdoes not meet airworthiness require-ments but is capable of safe flight. Aspecial flight permit can be issued tomove an aircraft for the purposes ofmaintenance or repair, buyer delivery,manufacturer flight tests, evacuationfrom danger, or customer demonstra-tion. Also referred to as a ferry permit.

spaced at 50-foot intervals beginning75 feet from the landing threshold.

RUNWAY EDGE LIGHTS—Acomponent of the runway lightingsystem that is used to outline theedges of runways at night or duringlow visibility conditions. These lightsare classified according to the inten-sity they are capable of producing.

RUNWAY END IDENTIFIERLIGHTS (REIL)—One componentof the runway lighting system. Theselights are installed at many airfields toprovide rapid and positive identifi-cation of the approach end of aparticular runway.

SEA BREEZE—A coastal breezeblowing from sea to land caused bythe temperature difference when theland surface is warmer than the seasurface. The sea breeze usually occursduring the day and alternates with theland breeze that blows in the oppositedirection at night.

SEA-LEVEL ENGINE—A recipro-cating aircraft engine having a ratedtakeoff power that is producible onlyat sea level.

SECTIONAL AERONAUTICALCHARTS (1:500,000)—Designedfor visual navigation of slow ormedium speed aircraft. Topographicinformation on these charts featuresthe portrayal of relief, and a judiciousselection of visual check points forVFR flight. Aeronautical informationincludes visual and radio aids to navi-gation, airports, controlled airspace,restricted areas, obstructions andrelated data.

SEMI-MONOCOQUE—A fuselagedesign that includes a substructure ofbulkheads and/or formers, along withstringers, to support flight loads andstresses imposed on the fuselage.

SERVICE CEILING—The maxi-mum density altitude where the bestrate-of-climb airspeed will produce a100 feet-per-minute climb at maxi-mum weight while in a clean configu-ration with maximum continuouspower.

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SPECIAL USE AIRSPACE—Airspace that exists where activitiesmust be confined because of theirnature.

SPECIFIC FUELCONSUMPTION—The amount offuel in pounds per hour consumed orrequired by an engine per brake horse-power or per pound of thrust.

SPEED—The distance traveled in agiven time.

SPIN—An aggravated stall thatresults in an airplane descending in ahelical, or corkscrew path.

SPIRAL INSTABILITY—A condi-tion that exists when the static direc-tional stability of the airplane is verystrong as compared to the effect of itsdihedral in maintaining lateral equi-librium.

SPIRALING SLIPSTREAM—Theslipstream of a propeller-driven air-plane rotates around the airplane. Thisslipstream strikes the left side of thevertical fin, causing the aircraft to yawslightly. Rudder offset is sometimesused by aircraft designers to counter-act this tendency.

SPOILERS—High-drag devices thatcan be raised into the air flowing overan airfoil, reducing lift and increasingdrag. Spoilers are used for roll controlon some aircraft. Deploying spoilerson both wings at the same time allowsthe aircraft to descend without gain-ing speed. Spoilers are also used toshorten the ground roll after landing.

STABILATOR—A single-piece hor-izontal tail surface on an airplane thatpivots around a central hinge point. Astabilator serves the purposes of boththe horizontal stabilizer and the eleva-tors.

STABILITY—The inherent qualityof an airplane to correct for conditionsthat may disturb its equilibrium, andto return or to continue on the originalflightpath. It is primarily an airplanedesign characteristic.

STAGNANT HYPOXIA—A type ofhypoxia that results when the oxygen-rich blood in the lungs isn’t moving,

STATIONARY FRONT—A frontthat is moving at a speed of less than 5knots.

STRATOSPHERE—A layer of theatmosphere above the tropopauseextending to a height of approxi-mately 160,000 feet.

STRESS MANAGEMENT—Thepersonal analysis of the kinds of stressexperienced while flying, the applica-tion of appropriate stress assessmenttools, and other coping mechanisms.

SUBLIMATIONProcess by whicha solid is changed to a gas withoutgoing through the liquid state.

SUPERCHARGER—An engine- orexhaust-driven air compressor used toprovide additional pressure to theinduction air so the engine can pro-duce additional power.

SUPERCOOLED WATERDROPLETS—Water droplets thathave been cooled below the freezingpoint, but are still in a liquid state.

SURFACE ANALYSIS CHART—Areport that depicts an analysis of thecurrent surface weather. Shows theareas of high and low pressure, fronts,temperatures, dewpoints, wind direc-tions and speeds, local weather, andvisual obstructions.

TAKEOFF DISTANCE — Thedistance required to complete anall-engines operative takeoff to the35-foot height. It must be at least 15percent less than the distancerequired for a one-engine inopera-tive engine takeoff. This distance isnot normally a limiting factor as it isusually less than the one-engineinoperative takeoff distance.

TAXIWAY LIGHTS—Omnidirectional lights that outline theedges of the taxiway and are blue incolor.

TAXIWAY TURNOFF LIGHTS—Flush lights which emit a steady greencolor.

for one reason or another, to the tis-sues that need it.

STALL—A rapid decrease in liftcaused by the separation of airflowfrom the wing’s surface brought on byexceeding the critical angle of attack.A stall can occur at any pitch attitudeor airspeed.

STANDARD ATMOSPHERE—Atsea level, the standard atmosphereconsists of a barometric pressure of29.92 inches of mercury (in. Hg.) or1013.2 millibars, and a temperature of15°C (59°F). Pressure and tempera-ture normally decrease as altitudeincreases. The standard lapse rate inthe lower atmosphere for each 1,000feet of altitude is approximately 1 in.Hg. and 2°C (3.5°F). For example, thestandard pressure and temperature at3,000 feet mean sea level (MSL) is26.92 in. Hg. (29.92 - 3) and 9°C(15°C - 6°C).

STANDARD EMPTY WEIGHT(GAMA)—This weight consists ofthe airframe, engines, and all items ofoperating equipment that have fixedlocations and are permanentlyinstalled in the airplane; includingfixed ballast, hydraulic fluid, unusablefuel, and full engine oil.

STANDARD-RATE-TURN—A turnat the rate of 3º per second whichenables the airplane to complete a360º turn in 2 minutes.

STANDARD WEIGHTS—Thesehave been established for numerousitems involved in weight and balancecomputations. These weights shouldnot be used if actual weights are avail-able.

STATIC STABILITY—The initialtendency an aircraft displays whendisturbed from a state of equilibrium.

STATION—A location in the air-plane that is identified by a numberdesignating its distance in inches fromthe datum. The datum is, therefore,identified as station zero. An itemlocated at station +50 would have anarm of 50 inches.

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TELEPHONE INFORMATIONBRIEFING SERVICE(TIBS)Telephone recording of areaand/or route meteorological briefings,airspace procedures, and special avia-tion-oriented announcements.

TERMINAL AERODROMEFORECAST (TAF)—A report estab-lished for the 5 statute mile radiusaround an airport. Utilizes the samedescriptors and abbreviations as theMETAR report.

TERMINAL RADAR SERVICEAREAS (TRSA)—Areas where par-ticipating pilots can receive additionalradar services. The purpose of theservice is to provide separationbetween all IFR operations and partic-ipating VFR aircraft.

THERMOSPHERE—The last layerof the atmosphere that begins abovethe mesosphere and gradually fadesaway into space.

THRUST—The force which impartsa change in the velocity of a mass.This force is measured in pounds buthas no element of time or rate. Theterm, thrust required, is generallyassociated with jet engines. A forwardforce which propels the airplanethrough the air.

THRUST LINE—An imaginary linepassing through the center of the pro-peller hub, perpendicular to the planeof the propeller rotation.

TORQUE—1. A resistance to turningor twisting. 2. Forces that produce atwisting or rotating motion. 3. In anairplane, the tendency of the aircraftto turn (roll) in the opposite directionof rotation of the engine and propeller.4. In helicopters with a single, mainrotor system, the tendency of the heli-copter to turn in the opposite directionof the main rotor rotation.

TORQUEMETERAn instrumentused with some of the larger recipro-cating engines and turboprop orturboshaft engines to measure thereaction between the propellerreduction gears and the engine case.

calibrated airspeed, true airspeedincreases as altitude increases; or for agiven true airspeed, calibrated air-speed decreases as altitude increases.

TRUE ALTITUDE—The verticaldistance of the airplane above sealevel—the actual altitude. It is oftenexpressed as feet above mean sealevel (MSL). Airport, terrain, andobstacle elevations on aeronauticalcharts are true altitudes.

TRUSS—A fuselage design made upof supporting structural members thatresist deformation by applied loads.The truss-type fuselage is constructedof steel or aluminum tubing. Strengthand rigidity is achieved by weldingthe tubing together into a series of tri-angular shapes, called trusses.

T-TAIL—An aircraft with the hori-zontal stabilizer mounted on the top ofthe vertical stabilizer, forming a T.

TURBINE DISCHARGEPRESSUREThe total pressure atthe discharge of the low-pressure tur-bine in a dual-turbine axial-flowengine.

TURBINE ENGINE—An aircraftengine which consists of an air com-pressor, a combustion section, and aturbine. Thrust is produced byincreasing the velocity of the air flow-ing through the engine.

TURBOCHARGER—An air com-pressor driven by exhaust gases,which increases the pressure of the airgoing into the engine through the car-buretor or fuel injection system.

TURBOFAN ENGINE—A fanliketurbojet engine designed to createadditional thrust by diverting a sec-ondary airflow around the combustionchamber.

TURBOJET ENGINE—A turbineengine which produces its thrustentirely by accelerating the airthrough the engine.

TURBOPROP ENGINE—A turbineengine which drives a propellerthrough a reduction gearing arrange-ment. Most of the energy in the

TOTAL DRAG—The sum of the par-asite and induced drag.

TOUCHDOWN ZONE LIGHTS—Two rows of transverse light bars dis-posed symmetrically about therunway centerline in the runwaytouchdown zone.

TRACK—The actual path made overthe ground in flight.

TRAILING EDGE—The portion ofthe airfoil where the airflow over theupper surface rejoins the lower sur-face airflow.

TRANSCRIBED WEATHERBROADCAST (TWEB)A contin-uous recording of weather and aero-nautical information broadcast overselected NDB or VOR stations.

TRANSPONDER—The airborneportion of the secondary surveillanceradar system.

TRICYCLE GEAR—Landing gearemploying a third wheel located onthe nose of the aircraft.

TRIM TAB—A small auxiliaryhinged portion of a movable controlsurface that can be adjusted duringflight to a position resulting in a bal-ance of control forces.

TROPOPAUSE—The boundarylayer between the troposphere and themesosphere which acts as a lid to con-fine most of the water vapor, and theassociated weather, to the tropo-sphere.

TROPOSPHERE—The layer of theatmosphere extending from the sur-face to a height of 20,000 to 60,000feet depending on latitude.

TRUE AIRSPEED (TAS)—Calibrated airspeed corrected for alti-tude and nonstandard temperature.Because air density decreases with anincrease in altitude, an airplane has tobe flown faster at higher altitudes tocause the same pressure differencebetween pitot impact pressure andstatic pressure. Therefore, for a given

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exhaust gases is converted into torque,rather than using its acceleration todrive the aircraft.

TURBOSHAFT ENGINEA gasturbine engine that delivers powerthrough a shaft to operate somethingother than a propeller.

TURN-AND-SLIP INDICATOR—A flight instrument consisting of a rategyro to indicate the rate of yaw and acurved glass inclinometer to indicatethe relationship between gravity andcentrifugal force. The turn-and-slipindicator indicates the relationshipbetween angle of bank and rate ofyaw. Also called a turn-and-bank indi-cator.

TURN COORDINATOR—A rategyro that senses both roll and yaw dueto the gimbal being canted. Haslargely replaced the turn-and-slipindicator in modern aircraft.

TURNING ERROR—One of theerrors inherent in a magnetic compasscaused by the dip compensatingweight. It shows up only on turns to orfrom northerly headings in theNorthern Hemisphere and southerlyheadings in the Southern Hemisphere.Turning error causes the compass tolead turns to the north or south and lagturns away from the north or south.

ULTIMATE LOAD FACTOR—Instress analysis, the load that causesphysical breakdown in an aircraft oraircraft component during a strengthtest, or the load that according to com-putations, should cause such a break-down.

UNCONTROLLED AIRPORT—An airport that does not have an oper-ating control tower. Two-way radiocommunications are not required atuncontrolled airports, although it isgood operating practice for pilots totransmit their intentions on the speci-fied frequency.

UNCONTROLLED AIRSPACE—Class G airspace that has not beendesignated as Class A, B, C, D, or E.It is airspace in which air traffic con-trol has no authority or responsibilityto control air traffic; however, pilots

vertical axis is called the z-axis or theyaw axis.

VERTICAL CARD COMPASS—Amagnetic compass that consists of anazimuth on a vertical card, resemblinga heading indicator with a fixedminiature airplane to accurately pres-ent the heading of the aircraft. Thedesign uses eddy current damping tominimize lead and lag during turns.

VERTICAL SPEEDINDICATOR—An instrument thatuses static pressure to display a rate ofclimb or descent in feet per minute.The VSI can also sometimes be calleda vertical velocity indicator (VVI).

VERTICAL STABILITY—Stabilityabout an aircraft’s vertical axis. Alsocalled yawing or directional stability.

VERY HIGH FREQUENCY(VHF) OMNIDIRECTIONALRANGE (VOR)—A ground-basedelectronic navigation aid transmittingvery high frequency navigation sig-nals, 360 degrees in azimuth, orientedfrom magnetic north. Used as thebasis for navigation in the NationalAirspace System. The VOR periodi-cally identifies itself by Morse Codeand can have an additional voice iden-tification feature. Voice features canbe used by ATC or FSS for transmit-ting instructions/ information topilots.

VFE—The maximum speed with theflaps extended. The upper limit of thewhite arc.

VFR TERMINAL AREA CHARTS(1:250,000)—Depict Class B airspacewhich provides for the control or seg-regation of all the aircraft within theClass B airspace. The chart depictstopographic information and aeronau-tical information which includesvisual and radio aids to navigation,airports, controlled airspace,restricted areas, obstructions, andrelated data.

V-G DIAGRAM—A chart thatrelates velocity to load factor. It isvalid only for a specific weight, con-figuration and altitude and showsthe maximum amount of positive or

should remember there are VFR mini-mums which apply to this airspace.

USEFUL LOAD—The weight of thepilot, copilot, passengers, baggage,usable fuel, and drainable oil. It is thebasic empty weight subtracted fromthe maximum allowable gross weight.This term applies to general aviationaircraft only.

VA—The design maneuvering speed.This is the “rough air” speed and themaximum speed for abrupt maneu-vers. If during flight, rough air orsevere turbulence is encountered,reduce the airspeed to maneuveringspeed or less to minimize stress on theairplane structure. It is important toconsider weight when referencing thisspeed. For example, VA may be 100knots when an airplane is heavilyloaded, but only 90 knots when theload is light.

VAPOR LOCK—A condition inwhich air enters the fuel system and itmay be difficult, or impossible, torestart the engine. Vapor lock mayoccur as a result of running a fuel tankcompletely dry, allowing air to enterthe fuel system. On fuel-injectedengines, the fuel may become so hot itvaporizes in the fuel line, not allowingfuel to reach the cylinders.

VARIATION—The angular differ-ence between the true, or geographic,poles and the magnetic poles at agiven point. The compass magnet isaligned with the magnetic poles, whileaeronautical charts are oriented to thegeographic poles. This variation mustbe taken into consideration whendetermining an aircraft’s actual geo-graphic location. Indicated on chartsby isogonic lines, it is not affected bythe airplane’s heading.

VECTOR—A force vector is agraphic representation of a force andshows both the magnitude anddirection of the force.

VELOCITY—The speed or rate ofmovement in a certain direction.

VERTICAL AXIS—An imaginaryline passing vertically through thecenter of gravity of an aircraft. The

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negative lift the airplane is capableof generating at a given speed. Alsoshows the safe load factor limits andthe load factor that the aircraft cansustain at various speeds.

VISUAL APPROACH SLOPEINDICATOR (VASI)—The mostcommon visual glidepath system inuse. The VASI provides obstructionclearance within 10° of the extendedrunway centerline, and to 4 nauticalmiles (NM) from the runway thresh-old.

VLE—Landing gear extended speed.The maximum speed at which an air-plane can be safely flown with thelanding gear extended.

VLO—Landing gear operating speed.The maximum speed for extending orretracting the landing gear if using anairplane equipped with retractablelanding gear.

VMC—Minimum control airspeed.This is the minimum flight speed atwhich a light, twin-engine airplanecan be satisfactorily controlled whenan engine suddenly becomes inopera-tive and the remaining engine is attakeoff power.

VNE—The never-exceed speed.Operating above this speed is prohib-ited since it may result in damage orstructural failure. The red line on theairspeed indicator.

VNO—The maximum structural cruis-ing speed. Do not exceed this speedexcept in smooth air. The upper limitof the green arc.

VOR—See VERY HIGH FRE-QUENCY (VHF) OMNIDIREC-TIONAL RANGE.

VS0—The stalling speed or the mini-mum steady flight speed in the land-ing configuration. In small airplanes,this is the power-off stall speed at themaximum landing weight in the land-ing configuration (gear and flapsdown). The lower limit of the whitearc.

VS1—The stalling speed or the mini-mum steady flight speed obtained in a

to vary the amount of exhaust gasesforced through the turbocharger tur-bine.

WEATHER DEPICTIONCHART—Details surface conditionsas derived from METAR and othersurface observations.

WEIGHT—A measure of the heavi-ness of an object. The force by whicha body is attracted toward the centerof the Earth (or another celestial body)by gravity. Weight is equal to the massof the body times the local value ofgravitational acceleration. One of thefour main forces acting on an aircraft.Equivalent to the actual weight of theaircraft. It acts downward through theaircraft’s center of gravity toward thecenter of the Earth. Weight opposeslift.

WIND CORRECTION ANGLE—Correction applied to the course toestablish a heading so that track willcoincide with course.

WIND DIRECTIONINDICATORS—Indicators thatinclude a wind sock, wind tee, ortetrahedron. Visual reference willdetermine wind direction and runwayin use.

WIND SHEAR—A sudden, drasticshift in windspeed, direction, or boththat may occur in the horizontal orvertical plane.

WINDS AND TEMPERATUREALOFT FORECAST (FD)—Atwice daily forecast that provideswind and temperature forecasts forspecific locations in the contiguousUnited States.

WING AREA—The total surface ofthe wing (square feet), which includescontrol surfaces and may includewing area covered by the fuselage(main body of the airplane), andengine nacelles.

WINGS—Airfoils attached to eachside of the fuselage and are the mainlifting surfaces that support the air-plane in flight.

specified configuration. For most air-planes, this is the power-off stallspeed at the maximum takeoff weightin the clean configuration (gear up, ifretractable, and flaps up). The lowerlimit of the green arc.

V-TAIL—A design which utilizestwo slanted tail surfaces to performthe same functions as the surfaces of aconventional elevator and rudder con-figuration. The fixed surfaces act asboth horizontal and vertical stabiliz-ers.

VX—Best angle-of-climb speed. Theairspeed at which an airplane gains thegreatest amount of altitude in a givendistance. It is used during a short-fieldtakeoff to clear an obstacle.

VY—Best rate-of-climb speed. Thisairspeed provides the most altitudegain in a given period of time.

VYSE—Best rate of climb speed withone engine inoperative. This airspeedprovides the most altitude gain in agiven period of time in a light, twin-engine airplane following an enginefailure.

WAKE TURBULENCE—Wingtipvortices that are created when an air-plane generates lift. When an airplanegenerates lift, air spills over thewingtips from the high pressure areasbelow the wings to the low pressureareas above them. This flow causesrapidly rotating whirlpools of aircalled wingtip vortices or wake turbu-lence.

WARM FRONT The boundaryarea formed when a warm air masscontacts and flows over a colder airmass. Warm fronts cause low ceilingsand rain.

WARNING AREAS—Areas thatmay contain hazards to nonpartic-ipating aircraft in internationalairspace. These areas are depictedon aeronautical charts.

WASTE GATE—A controllablevalve in the tailpipe of an aircraftreciprocating engine equipped with aturbocharger. The valve is controlled

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G-17

WING SPAN—The maximum dis-tance from wingtip to wingtip.

WINGTIP VORTICES—The rap-idly rotating air that spills over an air-plane’s wings during flight. Theintensity of the turbulence depends onthe airplane’s weight, speed, and con-figuration. Also referred to as waketurbulence. Vortices from heavy air-craft may be extremely hazardous tosmall aircraft.

WING TWIST—A design featureincorporated into some wings to

gation by moderate speed aircraft.Topographic information includes citiesand towns, principal roads, railroads,distinctive landmarks, drainage, andrelief. Aeronautical informationincludes visual and radio aids to naviga-tion, airports, airways, restricted areas,obstructions and other pertinent data.

ZULU TIME—A term used in avia-tion for coordinated universal time(UTC) which places the entire worldon one time standard.

improve aileron control effectivenessat high angles of attack during anapproach to a stall.

WORK—The product of force andthe distance through which the forceacts. Usually expressed in foot-pounds.

WORLD AERONAUTICALCHARTS (WAC) (1:1,000,000)—Provide a standard series of aeronauticalcharts covering land areas of the worldat a size and scale convenient for navi-

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G-18

Glossary.qxd 10/22/03 12:28 PM Page G-18

I -1

100-HOUR INSPECTION 7-7

AABBREVIATED WEATHER BRIEFING 11-4ABSOLUTE ALTITUDE 6-4ACCELERATE-GO DISTANCE 9-32ACCELERATE-STOP DISTANCE 9-32ADF 14-22ADIABATIC COOLING 10-12ADIABATIC HEATING 10-12ADJUSTABLE-PITCH PROPELLER 5-4ADVERSE YAW 4-2AERODYNAMIC FORCES IN FLIGHT

MANEUVERS 3-17climbs 3-19descents 3-19turns 3-17

AERONAUTICAL DECISION MAKING 16-1origins 16-2process 16-2factors 16-5

AILERONS 4-1differential 4-2coupled with rudder 4-3Frise-type 4-2

AIR CARRIER OBSTACLE CLIMBREQUIREMENTS 9-36

AIR DENSITY 2-2AIR MASSES 10-18AIR TRAFFIC CONTROL RADAR BEACON

SYSTEM 12-11AIR TRAFFIC CONTROL SERVICES 12-10AIRCRAFT 1-1

AIRCRAFT MAINTENANCE 7-7AIRCRAFT REGISTRATION 7-5AIRFOIL 1-3, 2-4

camber 2-4chord line 2-4ice controls 5-28laminar flow 2-5leading edge 2-4pressure distribution 2-6trailing edge 2-4

AIRMAN’S METEOROLOGICALINFORMATION 11-12

AIRMET 11-3, 11-12AIRPLANE 1-1AIRPLANE FLIGHT MANUAL 7-1

use of 14-13AIRPORT ADVISORY AREA 13-4AIRPORT BEACON 12-5AIRPORT FACILITY DIRECTORY 12-1

use of 14-13AIRPORT LIGHTING 12-5

control of 12-7AIRPORT MARKINGS 12-3

runway 12-3taxiway 12-3

AIRPORT SIGNS 12-3AIRPORTS

controlled 12-1uncontrolled 12-1

AIRSPACEClass A 13-1Class B 13-1Class C 13-1Class D 13-3Class E 13-3Class G 13-3

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I -2

controlled 13-1uncontrolled 13-3

AIRSPEEDcalibrated 6-6groundspeed 6-6indicated 6-6limitations 6-7true 6-6

AIRSPEED EQUIVALENT 9-18AIRSPEED INDICATOR 6-6

markings 6-6AIRWORTHINESS CERTIFICATE 7-6AIRWORTHINESS DIRECTIVES 7-10ALCOHOL 15-8ALERT AREA 13-4ALTIMETER 6-2

operation 6-4setting 6-3

ALTIMETER SYSTEM INSPECTION 7-8ALTITUDE

absolute 6-4density 6-5indicated 6-4pressure 6-4true 6-4

AMMETER 5-20ANNUAL INSPECTION 7-7 ANTISERVO TAB 1-4, 4-8APPROACH LIGHT SYSTEMS 12-6AREA FORECAST 11-10ARM 8-3ASOS 11-1ASYMMETRIC LOADING 3-25ATIS 6-3ATMOSPHERE 10-1ATMOSPHERIC CIRCULATION 10-5ATMOSPHERIC PRESSURE 2-2, 9-1, 10-3

effect of differences in air density 10-5effect on altitude 10-4

ATMOSPHERIC STABILITY 10-12ATTITUDE INDICATOR 6-12AUTOKINESIS 15-11AUTOMATED SURFACE OBSERVING SYSTEM 11-1AUTOMATED WEATHER OBSERVING

SYSTEM 11-1AUTOMATIC DIRECTION FINDER 14-22AUTOMATIC TERMINAL INFORMATION

SERVICE 6-3AUTOPILOT 5-23AVIATION ROUTINE WEATHER REPORT 11-4AWOS 11-1AXES OF AN AIRPLANE 3-8

BBALANCE 8-2

adverse effects 8-2

BALANCE TABS 4-8BALANCED FIELD LENGTH 9-32BASIC EMPTY WEIGHT 8-3BEACON 12-5BERNOULLI’S PRINCIPLE 2-3BIPLANE 1-3BOUNDARY LAYER 3-36BRAKE HORSEPOWER 5-31, 9-10BRAKE SPECIFIC FUEL CONSUMPTION 9-10BRAKES 5-23BUS BAR 5-20

CCALIBRATED AIRSPEED (CAS) 6-6CANARD 4-5CARBON MONOXIDE POISONING 15-6CARBURETOR 5-5

air temperature gauge 5-8heat 5-7icing 5-6

CEILING 10-17CENTER OF GRAVITY (CG) 2-7, 8-2, 8-3

determination 8-6limits 8-4range 8-4

CENTER OF LIFT 2-7CENTER OF PRESSURE 2-7CENTRIFUGAL FORCE 3-17CENTRIPETAL FORCE 3-17CHANDELLES 3-30CHARTING A COURSE 14-14CIRCULAR ARC AIRFOIL 2-5CLASS A AIRSPACE 13-1CLASS B AIRSPACE 13-1CLASS C AIRSPACE 13-1CLASS D AIRSPACE 13-3CLASS E AIRSPACE 13-3CLASS G AIRSPACE 13-3CLEARING PROCEDURES 12-14CLIMB PERFORMANCE 9-6CLIMB REQUIREMENTS, TRANSPORT CATEGORY

first segment 9-35fourth or final segment 9-35second segment 9-35second segment climb limitations 9-35third or acceleration segment 9-35

CLOUDS 10-15COLD FRONT 10-20COLLISION AVOIDANCE 12-14COMBUSTION 5-12COMPASS ERRORS

acceleration/deceleration 6-16deviation 6-16, 14-5, 14-12magnetic dip 6-16turning 6-16variation 6-15

COMPASS HEADING 14-12

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I -3

COMPRESSOR STALL 5-33CONDENSATION 10-13

nuclei 10-15CONTINUOUS FLOW OXYGEN SYSTEMS 5-27CONTROLLED AIRPORT 12-1CONTROLLED AIRSPACE 13-1CONTROLLED FIRING AREA 13-4CONVECTIVE CURRENTS 10-7CONVECTIVE SIGMET 11-3CONVECTIVE SIGNIFICANT METEOROLOGICAL

INFORMATION 11-12CONVENTIONAL GEAR 1-4COOLING SYSTEMS 5-18CORKSCREW EFFECT 3-24CREW RESOURCE MANAGEMENT 16-1CRM 16-1

D

DATUM 8-4DEAD RECKONING 14-10DECIDE MODEL 16-4DECISION-MAKING

process 16-2resources 16-7

DEHYDRATION 15-7DENSITY ALTITUDE 6-5, 9-3DEPOSITION 10-13DETONATION 5-12DEVIATION 6-16, 14-5, 14-12DEW 10-14DEWPOINT 10-13DIHEDRAL 3-14DILUTER DEMAND OXYGEN SYSTEMS 5-27DIRECT USER ACCESS TERMINAL SERVICE 11-2DISTANCE 14-12DISTANCE MEASURING EQUIPMENT 14-21DIVERSION 14-27DME 14-21DRAG 3-1, 3-3DRUGS 15-8DUATS 11-2DUTCH ROLL 3-16DYNAMIC STABILITY 3-11

EEDDY CURRENT DAMPING 6-17EFAS 11-2

effect on flight 10-4effect on wind 10-5

ELECTRICAL SYSTEM 5-19ELEVATOR 4-3

EMPENNAGE 1-4EMPTY-FIELD MYOPIA 15-10ENGINE

altitude 5-10cooling system 5-18pressure ratio (EPR) 5-32reciprocating 5-1sea-level 5-9turbine 5-29

ENROUTE FLIGHT ADVISORY SERVICE 11-2EQUILIBRIUM 3-10EQUIVALENT AIRSPEED 9-18EQUIVALENT SHAFT HORSEPOWER 5-31ERROR CHAIN 16-1ESTIMATED TIME EN ROUTE 14-12ETE 14-12EVAPORATION 10-13EXHAUST GAS TEMPERATURE 5-32EXHAUST SYSTEMS 5-19EXPLOSIVE DECOMPRESSION 5-25

FFAA FLIGHT SERVICE STATION 11-2FALSE HORIZON 15-11FATIGUE 15-7FILING A FLIGHT PLAN (VFR) 14-16FIREWALL 1-4FIXED LANDING GEAR 5-23FIXED-PITCH PROPELLER 5-3FLAMEOUT 5-33FLAPS 4-6FLIGHT COMPUTERS 14-8FLIGHT CONTROLS 4-1FLIGHT DIVERSION 14-27FLIGHT PLAN FILING (VFR) 14-16FLIGHT PLANNING 14-13FLIGHT WATCH 11-2FLOOR LOAD LIMIT 8-4FOG 10-14FOREIGN OBJECT DAMAGE (FOD) 5-32FORM DRAG 3-3FOUR STROKE CYCLE 5-2

compression 5-2exhaust 5-2intake 5-2power 5-2

FRONTS 10-18cold 10-20occluded 10-22stationary 10-22warm 10-19

FROST 10-14FSS 11-2FUEL

contamination 5-15

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I -4

drains 5-14gauges 5-14grades 5-15injection 5-8load 8-4primer 5-14pumps 5-14rate 14-12selectors 5-14strainers 5-14sumps 5-14systems 5-13tanks 5-14

FUSELAGE 1-2

GGAS DECOMPRESSION SICKNESS 5-26GLOBAL POSITIONING SYSTEM 14-26GPS 14-26GRAVITY 3-5GROUND ADJUSTABLE TABS 4-9GROUND EFFECT 3-7, 9-10GROUNDSPEED 6-6, 14-12GYROSCOPIC

action 3-24flight instruments 6-9principles 6-9rigidity in space 6-9

HHAZARDOUS ATTITUDES 16-6HAZARDOUS IN-FLIGHT WEATHER ADVISORY

SERVICE 11-3HEADING INDICATOR 6-12HEATSTROKE 15-7HIGH ALTITUDE PERFORMANCE ENGINE 5-11HIGH-SPEED FLIGHT 3-35

controls 3-40HIWAS 11-3HOT START 5-33HUMAN FACTORS 16-1HUMIDITY 2-2HUNG START 5-33HYDRAULIC SYSTEMS 5-22HYDROPLANING 9-14HYPERVENTILATION 15-3HYPOXIA 15-2

histotoxic 15-2hypemic 15-2hypoxic 15-2stagnant 15-2symptoms 15-2

I

IAS 6-6, 9-18I-BEAM 1-4ICE CONTROL SYSTEMS 5-28

airfoil 5-28propeller 5-29windscreen 5-29

IGNITION SYSTEM 5-11ILLUSIONS 15-4INCLINOMETER 6-11INDICATED AIRSPEED 6-6, 9-18INDICATED ALTITUDE 6-4INDUCED DRAG 3-3IN-FLIGHT WEATHER ADVISORIES 11-12INOPERATIVE EQUIPMENT OPERATIONS 7-8INSPECTIONS

100-hour 7-7aircraft 7-7altimeter system 7-8annual 7-7preflight 7-8transponder 7-8

INTERCOOLER 5-10INTERFERENCE DRAG 3-3INTERPOLATION 9-20INVERSION 10-13

LLAMINAR FLOW AIRFOIL 2-5LAND BREEZE 10-7LANDING GEAR 1-4

fixed 5-23retractable 5-23tailwheel 5-23tricycle 5-22

LANDING PERFORMANCE 9-17, 9-37LATERAL STABILITY 3-14LATITUDE 14-2LAZY EIGHTS 3-30LEADING EDGE DEVICES 4-7LICENSED EMPTY WEIGHT 8-4LIFT 3-1, 3-6LOAD FACTORS 3-26

flight maneuvers 3-29stalling speeds 3-28steep turns 3-27

LOADMETER 5-21LONGERON 1-2LONGITUDE 14-2LONGITUDINAL STABILITY 3-11LORAN-C 14-24

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I -5

LOST COMMUNICATION PROCEDURES 12-9LOST PROCEDURES 14-27LOW-LEVEL WIND SHEAR 10-9

M

MACH BUFFET BOUNDARIES 3-39MACH NUMBER 3-36MAGNETIC BEARING 14-23MAGNETIC COMPASS 6-14MAGNETIC DIP 6-16MAGNETIC HEADING 14-12MAGNETO 5-12MAGNUS EFFECT 2-3MANIFOLD ABSOLUTE PRESSURE (MAP) 5-4MASTER SWITCH 5-20MAXIMUM LANDING WEIGHT 8-4MAXIMUM RAMP WEIGHT 8-4MAXIMUM TAKEOFF WEIGHT 8-4MAXIMUM WEIGHT 8-4MAXIMUM ZERO FUEL WEIGHT 8-4MEAN AERODYNAMIC CHORD (MAC) 2-8, 8-4MEDICAL CERTIFICATE 15-1MEL 7-8MERIDIANS 14-2METAR 11-4MICROBURST 10-10MIDDLE EAR PROBLEMS 15-3MILITARY OPERATION AREA 13-4MILITARY TRAINING ROUTE 13-4 MINIMUM EQUIPMENT LISTS 7-8MIXTURE CONTROL 5-5MOA 13-4MOMENT 3-9, 8-4MOMENT INDEX 8-4MONOCOQUE 1-2MONOPLANE 1-3MOTION SICKNESS 15-6

NN1 INDICATOR 5-32N2 INDICATOR 5-32NACELLE 1-5NATIONAL SECURITY AREAS 13-5NAVIGATION

calculations 14-8measurement of direction 14-3wind effect 14-6

NDB 14-22NEGATIVE ARM COMPUTATIONS 8-8NEGATIVE STATIC STABILITY 3-10NEUTRAL STATIC STABILITY 3-10

NEWTON’S LAWS OF MOTION 2-2NIGHT VISION 15-10

autokinesis 15-11false horizon 15-11illusions 15-11, 15-12

NITROGEN 2-1NONDIRECTIONAL RADIOBEACON 14-22NOTAM 12-3NOTICES TO AIRMEN 12-3

OOBSTRUCTION LIGHTS 12-8OCCLUDED FRONT 10-22OIL SYSTEMS 5-16OPERATIONAL PITFALLS 16-9OUTLOOK WEATHER BRIEFING 11-4OUTSIDE AIR TEMPERATURE GAUGE 5-8, 6-17OVERBOOST 5-11OWNER RESPONSIBILITIES 7-11OXYGEN 2-1OXYGEN AND THE HUMAN BODY 10-2OXYGEN MASKS 5-27OXYGEN SYSTEMS 5-26

continuous flow 5-27diluter demand 5-27pressure demand 5-27servicing 5-28

PP FACTOR 3-23, 3-25PAPI 12-6PARACHUTE JUMP AREAS 13-4PARALLELS 14-2PARASITE DRAG 3-3

form 3-3interference 3-3skin 3-3

PAYLOAD 8-4PERFORMANCE 9-4

climb performance 9-6landing 9-17, 9-37range 9-8straight and level flight performance 9-5takeoff 9-15

PERFORMANCE CHARTS 9-19climb and cruise charts 9-23crosswind and headwind component chart 9-28density altitude charts 9-20landing charts 9-29stall speed performance charts 9-30takeoff charts 9-22

PILOT SELF-ASSESSMENT 16-5PILOT WEATHER REPORT 11-7

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I -6

PILOTAGE 14-10PILOT’S OPERATING HANDBOOK 7-1

use of 14-13PIREPS 11-7PITCH 3-9PITOT-STATIC FLIGHT INSTRUMENTS 6-1

blocked 6-8PLOTTER 14-8POWER 9-6POWERPLANT 1-5, 5-1PRECESSION 6-9PRECIPITATION 10-18PRECISION APPROACH PATH INDICATOR 12-6PREFLIGHT INSPECTIONS 7-8PREIGNITION 5-13PRESSURE ALTITUDE 6-4, 9-2PRESSURE DEMAND OXYGEN SYSTEMS 5-27PRESSURIZED AIRPLANES 5-24PREVENTIVE MAINTENANCE 7-9PRIMARY RADAR 12-10PROHIBITED AREA 13-3PROPELLER 5-2

adjustable-pitch 5-4fixed-pitch 5-3ice control 5-29principles 3-21

RRADAR OBSERVATION 11-2RADAR SUMMARY CHART 11-16RADAR TRAFFIC INFORMATION SYSTEM 12-11RADAR WEATHER REPORT 11-8RADIO COMMUNICATIONS 12-8RADIO EQUIPMENT 12-8RADIO LICENSE 12-8RADIOSONDE 11-1RANGE PERFORMANCE 9-8RECIPROCATING ENGINE 5-1REFUELING PROCEDURES 5-16REGION OF REVERSE COMMAND 9-12REIL 12-6RELATIVE BEARING 14-23RELATIVE HUMIDITY 9-4, 10-13REPAIRS AND ALTERATIONS 7-9RESTRICTED AREA 13-3RETRACTABLE LANDING GEAR 5-23RIB 1-3RIGIDITY IN SPACE 6-9RISK

assessing 16-5management 16-4

RNAV 14-21ROLL 3-9ROUGH AIR 3-30RUDDER 4-5

RUNWAY CENTERLINE LIGHTS 12-7RUNWAY EDGE LIGHTS 12-7RUNWAY END IDENTIFIER LIGHTS 12-6RUNWAY INCURSION AVOIDANCE 12-14RUNWAY MARKINGS 12-3RUNWAY SURFACE AND GRADIENT 9-13RUNWAY VISUAL RANGE 11-1RVR 11-1

SSCUBA DIVING 15-9SEA BREEZE 10-7SECTIONAL CHART 14-1SELF ASSESSMENT 16-5SEMI-MONOCOQUE 1-2SHOCK WAVES 3-37SIGMET 11-3, 11-12SIGNIFICANT METEOROLOGICAL

INFORMATION 11-12SIGNIFICANT WEATHER PROGNOSTIC

CHARTS 11-18SINUS PROBLEMS 15-3SITUATIONAL AWARENESS 16-8SKIN FRICTION DRAG 3-3SPAR 1-3SPATIAL DISORIENTATION 15-4SPECIAL FLIGHT PERMITS 7-9SPECIAL USE AIRSPACE 13-3

alert areas 13-4controlled firing area 13-4military operation area 13-4prohibited area 13-3restricted area 13-3warning area 13-4

SPINS 3-29SPIRAL INSTABILITY 3-16SPOILERS 3-40SPOILERS 4-7STABILATOR 1-4, 4-4STABILITY 3-10, 8-2

atmospheric 10-12dynamic 3-11lateral 3-14longitudinal 3-11static 3-10vertical 3-15

STABILIZER, ADJUSTABLE 4-9STALLS 3-20

high speed 3-29STANDARD EMPTY WEIGHT 8-4STANDARD WEATHER BRIEFING 11-3STANDARD WEIGHTS 8-4STARTING SYSTEM 5-16STATIC STABILITY 3-10

negative 3-10

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I -7

neutral 3-10positive 3-10

STATION 8-4STATIONARY FRONT 10-22STRAIGHT-AND-LEVEL FLIGHT

PERFORMANCE 9-5STRESS 15-6STRESS MANAGEMENT 16-6STRINGERS 1-3SUBLIMATION 10-13SUPERCHARGERS 5-9SUPERCOOLED WATER DROPLETS 10-15SUPERSONIC FLIGHT 3-35SURFACE ANALYSIS CHART 11-14SURFACE WEATHER MAPS 10-11SWEEPBACK WINGS 3-38

TTACHOMETER 5-3TAF 11-9TAS 6-6TAILWHEEL LANDING GEAR AIRPLANES 1-4, 5-23TAKEOFF PERFORMANCE 9-15TAXIWAY LIGHTS 12-8TAXIWAY MARKINGS 12-3TEMPERATURE/DEWPOINT SPREAD 10-13TEMPORARY FLIGHT RESTRICTIONS 13-4TERMINAL AERODROME FORECAST 11-9TERMINAL RADAR SERVICE AREAS 13-5THRUST 3-1, 3-2THRUST 9-6THRUST HORSEPOWER 5-31TIBS 11-2TIME ZONES 14-2TORQUE 3-23TORQUEMETER 5-32TOUCHDOWN ZONE LIGHTS 12-7TRANSCRIBED INFORMATION BRIEFING

SERVICE 11-2TRANSCRIBED WEATHER BROADCAST 11-3TRANSPONDER 12-11

inspection 7-8phraseology 12-12

TRANSPORT CATEGORY AIRPLANEPERFORMANCE 9-31

TRICYCLE LANDING GEAR AIRPLANES 1-4, 5-22TRIM TABS 4-8TRUE AIRSPEED 6-6, 9-18TRUE ALTITUDE 6-4TRUE COURSE 14-12TRUE HEADING 14-12TRUSS 1-2T-TAIL 4-3TURBINE ENGINE 5-29

turbofan 5-30

turbojet engines 5-30turboprop engines 5-30turboshaft engines 5-31

TURBINE ENGINE INSTRUMENTS 5-31TURBOFAN ENGINES 5-30TURBOJET ENGINES 5-30TURBOPROP ENGINES 5-30TURBOSHAFT ENGINES 5-31TURBOSUPERCHARGERS 5-10TURN COORDINATOR 6-11TURN-AND-SLIP INDICATOR 6-11TWEB 11-3TWIST 3-23

UUNCONTROLLED AIRPORT 12-1UNCONTROLLED AIRSPACE 13-3URGENT PIREP 11-3USEFUL LOAD 8-4

VV SPEEDS 6-7, 9-18VARIATION 6-15, 14-4, 14-12VASI 12-6VECTOR ANALYSIS 14-10VERTICAL CARD COMPASS 6-17VERTICAL SPEED INDICATOR 6-5VERTICAL STABILITY 3-15VERY HIGH FREQUENCY OMNIDIRECTIONAL

RANGE 14-18VFR ROUTES, PUBLISHED 13-4VFR TERMINAL AREA CHART 14-1VFR WEATHER MINIMUMS 13-2VG DIAGRAM 3-30VISIBILITY 10-18VISION IN FLIGHT 15-9VISUAL APPROACH SLOPE INDICATOR 12-6VISUAL GLIDESLOPE INDICATORS 12-6VOR 14-18

tracking 14-20use of 14-19

VOR/DME RNAV 14-21V-TAIL 4-6

WWAC CHARTS 14-1WAKE TURBULENCE 12-12WARM FRONT 10-19WARNING AREA 13-4WARREN TRUSS 1-2WASTE GATE 5-10

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I -8

WEATHER BRIEFINGabbreviated 11-4outlook 11-4standard 11-3

WEATHER DEPICTION CHART 11-15WEATHER MINIMUMS 13-2WEIGHT 3-1, 3-5WEIGHT AND BALANCE

computations 8-4effect of load distribution 3-33effect on airplane structure 3-32effect on performance 3-32effect on stability and controllability 3-33management 8-3terms 8-3

WEIGHT CONTROL 8-1WEIGHT SHIFT 8-9WIND 10-5

effect of obstructions 10-8patterns 10-6shift 10-21

WIND CORRECTION ANGLE 14-12WIND DIRECTION INDICATORS 12-8WIND PATTERNS 10-6WIND SHEAR 10-9WIND SHIFTS 10-21

WIND TRIANGLE 14-10WINDS AND TEMPERATURE ALOFT

FORECAST 11-13WINDSCREEN ICE CONTROL 5-29WING DIHEDRAL 3-14WINGS 1-3WINGTIP VORTICES 3-6, 12-13

avoidance procedures 12-13vortex behavior 12-13vortex generation 12-13vortex strength 12-13

WORK 9-6WORKLOAD MANAGEMENT 16-8WORLD AERONAUTICAL CHART 14-1

YYAW 3-9YAW STABILITY 3-15

ZZERO FUEL WEIGHT COMPUTATIONS 8-9

INDEX.qxd 10/22/03 12:26 PM Page I -8