Control System Servos

The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts.



Beechcraft Model 58 Baron

Overheated Pitch Servo

The pitch servo overheated, causing smoke in the cockpit. Investigation revealed the current-limiting resistor had melted. The pilot reported that 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

Beechcraft Model 300LW King Air

Uncommanded Pitch Inputs

Autopilot made uncommanded momentary pitch inputs at FL230 and then again at 4000 feet msl. Found elevator trim servo clutch out of tolerance and slipping. Adjusted the servo clutch to maintenance manual specs.

Part total time: 921.0 hours

Beechcraft Model B300 King Air

Intermittent Pitch Trim

Elevator trim annunciation took a long time to extinguish after engine start. Elevator trim in cruise flight was binding and immovable with autopilot on. A sudden nose-down pitch excursion was experienced but stabilized a few seconds after. Landing was uneventful. Maintenance replaced the elevator pitch trim servo (p/n 8221168003).

Part total time: 393.0 hours

Beechcraft Model 400A Beechjet

Intermittent Yaw Dampener

Aircraft experienced an intermittent yaw dampener fault—the autopilot would trip off while in turbulence. Troubleshooting found the rudder servo (p/n 622-6717-104) to be weak. The unit was removed from service and replaced with an overhauled item.

Part total time: Unknown

Cessna Model 172F Skyhawk

Binding Autopilot Servos

Elevator and aileron servos (p/n 8100064) stuck in flight. Owner/pilot cleared with force. Removed old unit and replaced with manufacturer’s new replacement part. Returned aircraft to service after complete test per manufacturer’s recommendations. Elevator servo had previously been changed for the same issue.

Part total time: Unknown

Cessna S550 Citation II

Porpoising Autopilot

At FL400, the autopilot started porpoising and was turned off. Afterward, the aircraft would not trim properly. The crew diverted; it was difficult to keep it pitched down while descending. During the final phase of flight, the yoke was very difficult to input pitch changes, but was okay in the roll axis. After landing, troubleshooting duplicated the problem. Elevator servo (p/n 4006719914) was replaced with serviceable unit.

Part total time: Unknown


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