office of aviation safety...configuration and aoa. • if airspeed too low, aoa required for level...
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Office of Aviation Safety
Aerodynamic Stalls at Low Altitude ICAO Mexico June 4, 2013
I Paul Cox Senior Air Safety Investigator
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Anyone Can Have a Bad Day
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• What is the origin of the title: • “Prevent Aerodynamic Stalls at Low
Altitude?”
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• Five Board Members • 400-Person Organization
– Office of Aviation Safety
–
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NTSB Facilitates Change Through….
• Accident Report Publications • Data Base Maintenance • Some Joint Effort Work • Outreach
• Safety Recommendations • Safety Accomplishments • Safety Results • Safety Alerts
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Where to Find These…
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Aviation Proverb • If you want to go up, pull back on the
yoke.
• If you want to go down, pull back a little more.
• If you want to go down real fast and spin around and around, just keep pulling back.
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FAA/Industry Cooperation • General Aviation Joint Steering
Committee (GAJSC) Loss of Control Work Group Approach and Landing
• 40.2% of the 1,259 fatal accidents 2001-2010 were “Loss of Control”
• 279 Accidents were approach and landing
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• Took 60 accidents, and used the first 30 that were well documented.
• Then developed a methodology to prioritize problems and interventions.
• Stressed the use of AOA systems.
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Forces on an Airplane
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Lift AoA
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Other Three Forces AoA
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Angle of Attack • Difference between the relative wind
and the wing chordline.
• AOA is primarily determined by aircraft speed and attitude.
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GearDownFS
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More Angle of Attack… • An element of lift, when AOA changes so
does the amount of lift produced. • Increased AOA is associated with
increasing CL up to max CL, then CL decreases.
• Critical AOA is at max CL
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Airspeed
• Controlled by power at a given configuration and AOA.
• If airspeed too low, AOA required for level flight will be so large that air cannot follow upper curvature of wing.
• Stall is from excessive AOA, not (directly) insufficient airspeed.
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Configuration • Flaps, landing gear, other devices
can affect stall speed.
• Device extension increases drag.
• Flap extension generally increases wing lift (white v. green arc.)
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Load Factor • Ratio of lifting force to weight of
airplane/contents.
• In a turn, increased load factors will cause an airplane’s stall speed to increase as angle of bank increases.
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Accelerated Stall • When an airplane stalls at a higher
indicated airspeed due to excessive maneuvering loads.
• Airplane stall speed increases in proportion to the square root of the load factor.
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Center of Gravity • As CG moves aft, the amount of
elevator deflection needed to stall is less. An increased AOA can be achieved with less elevator force.
• A forward CG can cause the stalling AOA to be reached at a higher airspeed.
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Performance numbers are really..
• The stall speed occurs at a particular angle of attack.
• Best glide speed occurs at a particular angle of attack.
• Best rate of climb speed occurs at a particular angle of attack.
• Best climb angle speed occurs at a particular angle of attack.
• Recommended approach speed is actually a recommended angle of attack.
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What is a stall? • Critical angle of attack is exceeded.
• Smooth airflow over the wing is disrupted.
• Can occur at any airspeed, any attitude, and
power setting.
• Gross weight affects the airspeed at which it can occur.
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What is a spin? • Critical AOA exceeded, with yaw.
• One wing “more stalled” than the other.
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What is a cross-controlled stall?
• Typically, rudder moves the airplane in one direction and ailerons in another.
• Results in rotation in the direction of rudder being applied, regardless of which wingtip is raised.
• Skidded Turn Stall • Slipping Turn Stall
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APS Training
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FCI
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Bruce Air
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Back Side of the Power Curve • Region of Reverse Command
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Arrest sink rate with nose up?
• Would be adding significant increase in induced drag with an increase in AOA.
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IASA-France
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Accident Investigation • (Wo)Man • Machine • Environment
• First collect the perishable data, then the rest.
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Main Wreckage • Wreckage Path • Leading Edges • Crush Angles
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Wing/Tail Breakage • In the Direction of the Spin
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DEN84FA308 Tabernash Co, CO • Cessna L-19E • August 10, 1984 • Found Aug 23, 1987 • 2 fatal • PC: None Stated (But narrative
discussed stall warning horn, 60-degree angle of bank and DA of 13,000 feet)
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ERA12FA196 Melbourne, FL • Cirrus SR22 • February 29, 2012 • 3 fatal • PC: The pilot's abrupt maneuver in response
to a perceived traffic conflict, which resulted in an accelerated stall and a loss of airplane control at low altitude. Contributing to the accident was the air traffic controller's incomplete instructions, which resulted in improper sequencing of traffic landing on the same runway.
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NYC01FA169 Medford, NJ • July 10, 2001 • 1 Fatal • PC: The pilot’s improper use of the
flight controls while turning to base, which resulted in a stall/spin and subsequent impact with the ground.
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DFW08FA060 Lindsay, OK • February 2, 2008 • 2 Fatal • The flight instructor’s failure to
maintain control of the airplane, which resulted in an inadvertent stall while maneuvering.
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AvWeb
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Ideas to Prevent Aero Stalls • Ground Preparations
• Utilize Imagineering
• In-Flight Preparations
• Pay Attention
•
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