FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsHard
During cruise flight with the autopilot engaged, a pilot notices the manual pitch trim wheel rotating nose-down continuously, and the aircraft begins a gradual descent despite ALT HOLD being selected. What is the most appropriate immediate action?
- ADisconnect the autopilot and manually trim the aircraft
- BSwitch the autopilot to vertical speed (VS) mode and monitor
- CIncrease the autopilot-commanded climb rate to counteract the trim movement
- DReduce power to match the unexpected descent
Show answer & explanationAnswer & explanation
Correct answer: A. Disconnect the autopilot and manually trim the aircraft
Continuous, uncommanded trim movement combined with an uncommanded descent is a classic sign of autopilot pitch trim runaway. The correct immediate response is to disconnect the autopilot (and autotrim if separate) and manually control pitch and trim to regain positive control, rather than attempting to work around the malfunction through other autopilot modes.
Why the other options are wrong
- B. Changing modes does not resolve a trim runaway malfunction and may not stop the trim motor.
- C. Adjusting climb rate does not address the underlying trim runaway and could worsen control difficulty.
- D. Reducing power does not correct the trim runaway and could compound the control problem.
Autopilot Trim Runaway
A malfunction where the autopilot's autotrim system continuously drives the trim in one direction, causing unexpected pitch changes; the correct response is immediate autopilot disconnect and manual trim correction.
- Signs include continuous trim wheel movement and unexpected pitch/altitude changes
- Immediate disconnect prevents worsening control difficulty
- Pilots should know the location of the autopilot disconnect switch and trim interrupt switch
Memory trick: Runaway trim? Disconnect first, ask questions later.