Autopilot Servos

The following information is derived from the FAA's Service Difficulty Reports and Aviation Maintenance Alerts.


Beech Model E55 Baron

Overtorqued Servo Clutch

Testing of the pitch servo’s clutch tension revealed breakaway force needed was 45 lbs. The specified setting is 13 ± 2 lbs. Examination revealed a new cotter pin on the castle nut and the orange torque seal strip did not align. At some point during previous maintenance, the castle nut securing the clutch on the servo was overtightened, which caused the breakaway force needed to be 30 lbs. too much.

Part total time: Unknown

Beech Model 58 Baron

Overheated Pitch Servo

The pitch servo (p/n 065001782200) overheated, causing smoke in the cockpit. The current-limiting resistor had melted. The pilot reported the aircraft had experienced some minor porpoising prior to the smoke. This is the third time this aircraft has experienced this problem and the third s/n with the same problem.

Part total time: Unknown

Beech B300 King Air

Intermittent Elevator Trim

Elevator trim annunciation took a long time to extinguish after engine start. Elevator trim in cruise flight was binding, with a sudden nose-down pitch input. No altitude loss. Replaced the elevator pitch trim servo and the aircraft was returned to service.

Part total time: 393.0 hours

Cessna 172F Skyhawk

Stuck Servos

Elevator and aileron servos stuck in flight. Pilot cleared with force. Removed old unit and replaced with new replacement part. Returned aircraft to service after testing per manufacturer recommendations. Elevator servo reportedly was changed previously.

Part total time: Unknown

Cessna 208B Grand Caravan

Smoking Pitch Servo

While en route, the pilot smelled smoke coming from aft compartment. Pilot diverted. Examination found the pitch servo was causing the smoke. Servo was replaced, aircraft returned to service.

Part total time: Unknown

Pilatus PC-12/47

Intermittent Stick Pusher

Pilot reported a stick- pusher CAS message during cruise flight. After landing, the stall warning circuit breakers were cycled but the message remained. Testing revealed the pusher servo was intermittent. It was replaced and the aircraft returned to service.

Part total time: Unknown

Piper PA-28R-180 Arrow

Failed Pitch Trim Servo

The pitch trim servo failed after approximately less than a year in service. Instrumentation displayed “AFCS preflight test failed” and “servo hardware fault” messages. The autopilot became inoperative. The servo displayed a “red” status light, indicating failure.

Part total time: 45.0 hours


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