This paper examines airplane response to rapid flap extension on seven general aviation airplanes. The scenario involves a pilot flying in the traffic pattern becoming distracted, abruptly extending flaps while looking outside the airplane, and failing to notice airspeed and pitch-attitude changes. The airplanes tested reached pitch forces of up to 36 lbf, meeting FAA requirements but exceeding the capability of 55% of the population. Flight data showed a pitch-up to more than 30˚ in 5 s after flap extension, causing airspeed to drop below stall speed for four of the airplanes. At traffic pattern altitudes, stalling an airplane can be fatal. The NTSB lists over 1000 accidents caused by loss of control in the traffic pattern between 1982 and 2017. As general aviation airplanes do not carry flight data recorders, it is unknown how many of those accidents may have involved stalls caused by uncommanded response after flap extension. From the data gathered in flight, it seems possible some were. To improve safety, flight training should prepare students to anticipate rapid pitch changes during flap extension and retraction. In addition, 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 14 CFR §23.143 to 20 lbf or less.
Kimberlin, Ralph; Wilde, Markus; Kish, Brian; and Silver, Isaac
"Airplane Pitch Response to Rapid Configuration Change: Flight Test and Safety Assessment,"
Journal of Aviation Technology and Engineering:
2, Article 7.
Available at: https://doi.org/10.7771/2159-6670.1216