What happened
While flying at 2,300 feet, the pilot of the aircraft shut off the autopilot. Immediately following this action, the pilot was unable to maintain pitch control, and the airplane entered a series of uncontrollable gyrations. Despite attempts by the pilot to regain control of the aircraft, the flight continued until the airplane collided with trees located five miles west of Baxley Municipal Airport.
The investigation
A post-accident functional examination of the autopilot assembly was conducted. The investigation disclosed that when the unit was engaged, the pitch servo would only correct the pitch attitude in one direction. An internal examination of the pitch servo revealed that three transistors had been replaced, while one transistor appeared to be original to the unit. Additionally, a functional check of the pitch trim servo solenoid revealed that the unit was not within design specifications.
Findings
The investigation noted that according to the pilot operating handbook, if the autopilot is disengaged while encountering opposing mistrim forces, the pilot may be required to exert control forces exceeding 50 pounds to maintain the airplane's attitude. The pilot must maintain this significant control force while manually retrimming the airplane.