Winter Operations

Re-current training

Common standards, regulation and recommendationsEffects of frost, ice, snow, slush on airplane performanceMeteorological considerations on ice formationBasic characteristics of airplane de-icing/anti=icing fluids, including causes and consequences of fluid degradation and residuesGeneral techniques for removing deposits of frost, ice, slush and snow from airplane surfaces and for anti-icingDe-icing/anti=icing procedures in general and specific measures to be performed on different airplane types and de-icing using hot airAirplane in general and common critical areasTypes of checks requiredSafety precautions and human factorsFluid application and limitations of holdover time tablesDe-icing/anti-icing codes and communication procedures (RT/E)New procedures, new development and alternative technology, lessons learned from previous wintersCondition which can lead to the formation of ice on the airplaneLocal rules and restrictionsAirport operational procedures and ATCCompany proceduresDe-icing coordination procedures in general

Pre-flight Procedures• Critical Surfaces• Walk-around• Aircraft SystemsDe-ice Anti-ice

Procedures• Detection & Removal• Procedures• Use of Holdover Times

Flight Procedures• Aircraft Systems• Procedures

Overview

Here are the topics for this lesson.

Ops Spec 023

Icing Conditions

• Icing conditions exist when OAT (on the ground) or TAT (in-flight) is 10°C or below and:– visible moisture (clouds, fog with visibility less

than one statute mile (1600 m), rain, snow, sleet, ice crystals, and so on) is present, or

– standing water, ice, or snow is present on the ramps, taxiways, or runways.

Clean Aircraft Concept

The aerodynamic effectiveness of an airframe requires that it begins flight with critical surfaces free from contamination by frozen or semi-frozen moisture (‘contaminant’). This is called the ‘clean aircraft’ concept.

The clean-airplane concept describes an airplane that is aerodynamically clean — that is, free of frozen contaminants. The clean-airplane concept is important because airplane takeoff performance is based upon clean surfaces until liftoff.

An airplane is designed using the predictable effects of airflow over clean wings. Contaminants such as frost, ice, or snow adhering to the wings disturb this airflow, resulting in reduced lift, increased drag, increased stall speed, potentially severe roll problems due to uneven lift, and possible abnormal pitch characteristics.

FAR 121.629

• (b) No person may take off an aircraft when frost, ice, or snow is adhering to the wings, control surfaces, propellers, engine inlets, or other critical surfaces of the aircraft ...

The “clean-airplane” concept is derived from U.S. Federal Aviation Administration (FAA) Federal Aviation regulation (FAR) 121.629 paragraph b, and FAR 125.221.

The FAR also prohibits dispatch or takeoff any time conditions are such that frost, ice, or snow may reasonably be expected to adhere to the airplane, unless the certificate holder has an approved ground deicing/anti-icing program in its operations specifications that includes holdover time (HOT) tables.

Icing Conditions

• Icing conditions exist when OAT (on the ground) or TAT (in-flight) is 10°C or below and:– visible moisture (clouds, fog with visibility less

than one statute mile (1600 m), rain, snow, sleet, ice crystals, and so on) is present, or

– standing water, ice, or snow is present on the ramps, taxiways, or runways.

Failure to remove contamination from an aircraft and/or to protect it from acquiring further contamination before it becomes airborne may result in sudden loss of control at or shortly after take off. In the case of aircraft with rear mounted engines, any ice on the inner wings of an aircraft at take off may be shed and ingested into the engines causing a partial or total loss of thrust. Intake duct deposits and engine blade deposits may detach and be ingested by the engine(s) during the subsequent application of high power settings for takeoff, with consequential adverse effects on engine operation, and possible flameout. DefencesTo protect against loss of control, the following precautions should be taken prior to flight in weather conditions which are or have recently been conducive to ice accretion: •A thorough inspection of all the airframe critical surfaces to establish if any existing contaminant is present; the prevailing surface temperature of the aircraft skin is as important as the prevailing Outside Air Temperature (OAT). •A consideration of the weather conditions which prevail - and are likely to prevail - after the start of any treatment of ice already on an aircraft to determine if anti-icing is necessary. •The correct application of appropriate De-Icing Fluids and/or Anti-Icing Fluids and the correct use of the De/Anti-Icing Code to help prevent any mis-understandings. •The determination and monitoring of the applicable Holdover Time by the flight crew so that take off is not attempted if it cannot be completed within that time. It is important to note that the applicable Holdover Time may change if prevailing conditions change. •Not taking off if there is no applicable holdover time for the weather conditions which have prevailed at any time since the commencement of ground anti-icing (this applies for Heavy Snow, Hail (defined as ice pieces between 5 and 50mm diameter), Snow or Ice Pellets (defined as hail of less than 5mm in diameter) and Moderate or Heavy Freezing Rain. •Care to reduce holdover times if the effect of either jet blast or high wind speeds indicate that this would be prudent. •Detection of snow or slush within an engine nacelle may be difficult or even impossible using normal visual inspection; and removal of contaminants may be equally difficult. Therefore, every effort should be made to prevent the ingress of snow, rain, etc. by the use of engine inlet covers and plugs. However, it is vital that these are both properly secured and that their fitment is recorded in the Aircraft Technical Log. Should they become dislodged and disappear inside the inlet of a turboprop engine to the extent that they are no longer visible, it will be evident that they have not been lost externally and that engineering assistance must be sought. Details of a fatal accident which highlighted the importance of this procedure can be seen at the accident report listed under 'Further Reading' below. •In all respects, relevant aircraft manufacturer recommendations should be followed. Where appropriate guidance is not provided, aircraft operators should liaise with manufacturers, regulators and other qualified entities to obtain advice which will enable them to develop suitable procedures. Such procedures should be described in Operations Manuals.

It is crucial to the effectiveness of aircraft ground de/anti icing that the aircraft commander receives accurate information on the fluid treatment carried out. This should be achieved by the use of a standard format Anti Icing Code to ensure that there is no possibility of mis-understanding in respect of the minimum required information. Relevant additional information can and should be passed as well. The Anti Icing Code Procedure, as described in the AEA Guidelines (see further reading), should be incorporated in the operational procedures for all aircraft operators and de-icing service providers. The Code communicates the following information to the aircraft commander by referring to the last step of the fluid treatment procedure in the following sequence: •the fluid type - Type 1 Fluid, Type 2 Fluid, Type 3 Fluid or Type 4 Fluid •the fluid concentration within the fluid/water mixture, expressed as a percentage by volume (this is not required for Type 1 Fluid) •the local time in hours and minutes at the beginning of the final (or only) de-icing/anti-icing step •(optionally,for Type 2 and 4 Fluids only) the complete name of the anti-icing fluid (the “brand name”) •the statement "post de-icing/anti-icing check completed". By Example: A de-icing/anti-icing procedure in which the last step was the use of a mixture of 75% of a type 2 fluid and 25% water which commenced at 1335 local time is communicated as follows: “TYPE 2/75 1335 [optional complete name of anti-icing fluid] post de-icing/anti-icing check completed” Communication of the anti icing code and any related supplementary information can be by R/T, intercom or message board display. For Record keeping purposes at the service provider, the date of the treatment should also be recorded in the sequence day, month, year.

Contamination Check

• By checking representative surfaces, this check ensures that snow, ice, or frost, is not adhering to the wings, control surfaces, engine inlets, or other critical surfaces defined in the aircraft operations manual.

When the holdover time has been exceeded or at any other time deemed appropriate by the PIC, takeoff will not be attempted until a contamination check has been accomplished.

representative surfaces are surfaces which can be readily observed by flight crew during day and night operations, and which are suitable for judging whether or not critical surfaces are contaminated.

critical surfaces: wings, ailerons, flaps, spoilers, rudder, horizontal & vertical tail surfaces fuselage, engines, APU and instrument probes/sensors.

Cold Weather Pre-flight Inspection

During your walk-around you determine whether de-icing/anti-icing is required.

Critical Surfaces

• Wings• Control surfaces

– Ailerons– Flaps– Spoilers– Rudder

• Horizontal tail surfaces• Fuselage• Vertical tail surfaces• Engines and APU

All critical aircraft surfaces should be clear of ice, snow, and frost prior to takeoff. Even thin layers of frost may cause substantial performance and handling degradation. Remember that clear ice may not be easy to detect visually.

Control Surfaces & Flaps

• Surfaces– Takeoff with light coatings of

frost, up to 1/8 inch (3mm) in thickness on lower wing surfaces due to cold fuel is permissible; however, all leading edge devices, all control surfaces, and upper wing surfaces must be free of snow or ice.

– Thin hoarfrost is acceptable on the upper surface of the fuselage provided all vents and ports are clear.

The gaps between fixed surfaces and movable surfaces such as elevators, rudders, ailerons, and flaps may become contaminated and prevent full deflection. Contamination with slush may allow the controls to operate in an apparently normal fashion on the ground but freeze at higher altitudes. Verify visually that all flap and control surface gaps are free from contamination.

Pitot/Static Probes & Static Ports

• Pitot/static probes and static ports

Verify that all pitot/static probes and static ports are free of snow and ice. Water rundown after snow removal may freeze immediately forward of static ports and cause an ice buildup which disturbs airflow over the static ports resulting in erroneous static readings even when static ports are clear.

Vents, Inlets & Doors

• Check free of snow and ice:– Air conditioning inlets and exits– Engine inlets– Fuel tank vents– Landing gear doors– APU air inlet

Check that all inlets, exits, vents and landing gear doors are free of snow and ice.

Procedures Review

• Definitions• Operating Procedures

Takeoff - Wet or Contaminated Runway Conditions

• Do not use reduced thrust (assumed temperature method) for takeoff if the runway is contaminated by slush, snow, standing water, or ice.

• Reduced thrust (fixed de-rate) takeoff is allowed on wet or contaminated runways provided takeoff performance accounts for the runway surface condition.

• Takeoffs are not recommended when slush, wet snow, or standing water depth is more than 1/2 inch (13 mm) or dry snow depth is more than 4 inches (102 mm).

Icing Conditions

• Icing conditions exist when OAT (on the ground) or TAT (in-flight) is 10°C or below and:– visible moisture (clouds, fog with visibility less

than one statute mile (1600 m), rain, snow, sleet, ice crystals, and so on) is present, or

– standing water, ice, or snow is present on the ramps, taxiways, or runways.

Engine Anti-ice Ground

• Engine anti-ice must be selected ON immediately after both engines are started and remain on during all ground operations when icing conditions exist or are anticipated, except when the temperature is below –40°C OAT.

• When engine anti-ice is required and the OAT is 3°C or below, do an engine run up, as needed, to minimize ice build-up.– Run-up to a minimum of 60% N1 for approximately 30 seconds

duration at intervals no greater than 30 minutes.

• When engine anti-ice is required and the OAT is 3°C or below,

the takeoff must be preceded by a static engine run-up.

Fan Ice Removal

• If moderate to severe icing conditions are encountered:– During flight in moderate to severe icing

conditions for prolonged periods with N1 settings at or below 70%, or if fan icing is suspected due to high engine vibration, increase thrust on one engine at a time to a minimum of 70% N1 for 10 to 30 seconds every 10 minutes.

Cold Temperature Altitude Corrections

• Consider altitude correction procedures when operating at or near airports where high terrain and/or obstacles exist in combination with very cold temperatures (-30°C or colder), or when en route minimum altitudes are affected by terrain clearance.

Inspections/Checks

• Cold Weather Preflight Inspection

• Pre-takeoff Check- Always Performed

• Contamination Check- Performed if holdover time exceeded or fluid breakdown suspected– Pre-flight Contamination Check

These are special inspection checks associated with cold weather operations. You need to look more closely to understand the slight differences between them.

Pre-takeoff check

• After completion of the de-icing/anti-icing application to ensure all aircraft critical surfaces are free of frozen contaminates

• This check is accomplished just prior to takeoff within the holdover time computed for the existing conditions.

Pre-Takeoff Contamination check

• Completed when the holdover time has been exceeded and that the takeoff must be completed within 5 minutes from takeoff

• Conducted by a flight crewmember to determine if the aircraft’s critical surfaces are contaminated by frost, ice, slush or snow.

Pre-Takeoff Contamination check

• Always required in Icing Conditions–Regardless of holdover time

• Turn ON- wing lights• Look out windows• Use Tail Camera as a back-up• Conduct within 5 minutes of takeoff

Takeoff - Wet or Contaminated Runway Conditions

• Reduced thrust (fixed de-rate) takeoff is allowed on wet or contaminated runways provided takeoff performance accounts for the runway surface condition.

• Takeoffs are not recommended when slush, wet snow, or standing water depth is more than 1/2 inch (13 mm) or dry snow depth is more than 4 inches (102 mm).

Engine Anti-ice Ground

• Engine anti-ice must be selected ON immediately after both engines are started and remain on during all ground operations when icing conditions exist or are anticipated, except when the temperature is below –40°C OAT.

• When engine anti-ice is required and the OAT is 3°C or below, do an engine run up, as needed, to minimize ice build-up.– Run-up to a minimum of 60% N1 for approximately 30 seconds

duration at intervals no greater than 30 minutes.

• When engine anti-ice is required and the OAT is 3°C or below,

the takeoff must be preceded by a static engine run-up.

Fan Ice Removal

• If moderate to severe icing conditions are encountered:– During flight in moderate to severe icing

conditions for prolonged periods with N1 settings at or below 70%, or if fan icing is suspected due to high engine vibration, increase thrust on one engine at a time to a minimum of 70% N1 for 10 to 30 seconds every 10 minutes.

Ice Crystal Icing Non-Normal

Ice Crystal Icing Non-Normal cont.

After Landing

Secure Procedure additions

• PACK CONTROL selectors …… AUTO• Cabin altitude mode selector.....MAN• Cabin altitude manual control.....DESCEND– Position the outflow valve fully closed to inhibit

the intake of snow or ice.• Wheel chocks.....Verify in place• Parking brake...... Released– Reduces the possibility of frozen brakes.

Typical Scenarios•Failure to get airborne attributed to failure to ground de-ice beforehand. •Loss of control shortly after an overweight take off in freezing precipitation and without ground de-icing of ice seen on the airframe prior to departure. •Loss of control during flap retraction after take off attributed to failure to ground de-ice prior to take off. •High speed Rejected Take Off (RTO) after a significant elevator split attributed to undetected ice in the elevator leading edge gap developed during the take off roll. •Loss of Control shortly after take off after both engines failed, because ice was not removed from the wings before departure and was shed from the wings and ingested after take off.

Winter Operations Test

a) A check of representative surfaces to ensure that snow, ice, or frost is not adhering to the wings, control surfaces, engine inlets, or other critical surfaces defined in the aircraft’s AOM.

b) An inspection performed by the fight crew to determine whether de-icing/anti-icing is required.

c) Any walk-around done in weather less than 0⁰ C.

A Cold Weather Preflight inspection is:

Which of the following is NOT a critical surface as defined by Aramco:

a) Fuselageb) Engines and APUc) Landing Gear

Type IV fluids are designed for Ice retardation and are not used for ice removal.

a) Trueb) False

A pre-takeoff contamination check must be performed by the flight crew any time icing conditions are present.

a) Trueb) False

What other ground operations can cause ice accumulation?

a) Ambient temperatures are below freezing and moisture such as slush, or snow is on ramps, taxiways, and runways.

b) Dry snow blown by winds, other aircraft, or ground support equipment.

c) Both a and b.

Angle of attack sensors automatically adjust for the effects of contamination on the wings.

a) Trueb) False

Select the correct statement:

a) It is not necessary to remove contaminates from control surfaces before anti-icing.

b) For maximum effectiveness and minimum consumption, the de-icing solution should be only luke warm.

c) Apply only enough fluid to remove the ice and snow or to leave a light coating of fluid on the aircraft.

If the anti-ice switches are OFF, the ice detection system does NOT provide indications of icing conditions.

a) Trueb) False

Wind tunnel flight tests indicate that ice, frost, or snow formations on the leading edge and upper surface of the wing, having a thickness and surface roughness similar to medium or coarse sandpaper, can reduce wing lift by as much as 30% and increase airplane drag by 40%.

a) Trueb) False

When required, a pre-takeoff contamination check is conducted by a flight crewmember immediately before takeoff to determine if the aircraft’s critical surfaces are contaminated by frost, ice, slush or snow. This check is to be completed when the holdover time is exceeded and that the takeoff must occur within ______ minutes of accomplishing this check.

a) 1 minuteb) 5 minutesc) 15 minutes