Autopilot Malfunctions

The following information is derived from maintenance facility submissions to the FAA's Service Difficulty Reports database.


Cessna 208B Grand Caravan

Uncommanded Pitch Down

The pilot reported the Garmin GFC 600 autopilot engaged uncommanded and pitched the aircraft nose down. Autopilot would not remain disengaged. At this writing, maintenance has not determined cause of failure. Autopilot system was installed 74.4 hours and 32 days before occurrence.

Part total time: 74.4 hours

Cessna 208B Grand Caravan

Porpoising In Pitch

Two crews reported the aircraft had a slight porpoising movement with autopilot on and altitude hold selected. With the autopilot off, the aircraft did not porpoise or indicate any altitude changes. The Garmin GFC 600 autopilot was disabled and deferred for maintenance.

Part total time: Unknown

Cessna 208B Grand Caravan

Uncommanded Pitch Down

While en route in light icing, the pilot noticed airspeed decaying faster than normal. While he inspected the wing for ice accumulation, the low airspeed warning went off. Pilot’s ASI indicated 100 KIAS while copilot’s read 130. The airplane then announced low airspeed and pitched over; the pilot held down the autopilot disconnect switch until ESP turned off. Pilot reversed course to return. Two more times during the descent, the Garmin GFC 600 autopilot re-engaged itself with ESP off and tried to pitch down. At around 2000 feet, the pilot-side airspeed began working again and the pilot landed uneventfully.

Part total time: 1452.0 hours

Epic LT

Malfunctioning Pitch Servo

Aircraft experienced a failure of the pitch trim actuator (p/n 0108-15-P2) in flight after the S-Tec autopilot trimmed the pitch to the full nose-down position.

Part total time: Unknown

Pilatus PC-12/45

Faulty Mode Controller

On descent, the autopilot disconnected, followed by electrical odor and smoke in cockpit. The crew declared an emergency and landed without further incident. The Honeywell autopilot mode controller was found to be faulty and the source of the electrical odor. The mode controller (p/n 065-00086-0017) was replaced.

Part total time: 2230.0 hours

Pilatus PC-12/47E

Jammed Ailerons

At FL230 while in IMC, the autopilot tripped off. Ailerons were jammed, pitch control normal. Much higher control wheel pressure required to roll. Partial jam remained until about 2500 feet msl.

Part total time: Unknown


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