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 detail autopilot malfunctions causing uncommanded flight path changes, such as rapid descents, abrupt climbs, and electric trim runaways.
• A significant safety issue is the repeated failure of primary and secondary autopilot disconnect switches, forcing pilots to resort to pulling circuit breakers or shutting off the avionics master switch to regain control.
• Autopilot failures can also lead to secondary issues like electrical odors/smoke and jammed flight controls, with some reported problems being chronic and persistent.

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