Autopilots

While in IFR cruise at 4000 feet, the pilot observed the flight director command bars move out of view as the airplane started a gradual descent. When the pilot corrected, the electric trim started to run nose down and the aircrafts descent rate increased. The pilot attempted to disconnect the autopilot and trim with the control switches and the red disconnect switch. None of this had any effect. With the turbulence and conditions, the pilot was unable to reach the autopilot and electric trim circuit breakers. After all other remedial procedures had failed, he shut off the avionics master switch at about 1000 feet and recovered the airplane at about 500 feet.

Key Takeaways:

• Multiple incidents involved autopilot malfunctions causing uncommanded aircraft pitch changes, often leading to rapid descents or abrupt climbs.
• In several cases, standard autopilot disconnect switches failed, forcing pilots to resort to pulling circuit breakers or shutting off the avionics master switch to regain control.
• Autopilot failures were attributed to various issues, including faulty mode controllers resulting in electrical smoke, and mechanical problems like jammed ailerons.
• Some aircraft experienced chronic autopilot instability, posing safety concerns and requiring recurring, unconventional remedies.

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