This paper examines airplane response to flap extension on four general aviation (GA) airplanes. The scenario involves a pilot flying in the traffic pattern who becomes distracted, abruptly extends flaps while looking outside the airplane, and fails to notice airspeed and pitch-attitude changes. In the Code of Federal Regulation (CFR) ¿¿23.143, the Federal Aviation Administration (FAA) requires no more than 50 pounds of pitch wheel force to arrest any un-commanded airplane pitch response [1]. The airplanes tested in this report had pitch forces less than 40 pounds. Despite satisfying the FAA requirement, data gathered in-flight showed a pitch-up to more than 30 degrees in 5 seconds after flap extension, subsequently causing airspeed to drop below stall speed for three of the airplanes. If the pilot did not compensate for this response with positive pitch inputs on the controls, the airplanes would have stalled. At traffic pattern altitudes, stalling an airplane can be fatal. The National Transportation Safety Board listed over 1000 accidents caused by loss-of-control in the traffic pattern between 1982 and 2015 [2]. Since GA airplanes don't carry flight data recorders, we don't know how many of those accidents may have involved stalls caused by un-commanded response after flap extension. From the data we gathered in-flight, it seems possible some were. To improve safety, airplane developers could interconnect flaps with the elevator, reduce horizontal tail size, or use a T-tail. The FAA should consider reducing the maximum pitch stick and wheel forces in CFR ¿¿23.143 to 10 pounds or less.
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