Incident Overview
During cruise at 8,500 feet, the aircraft experienced an in-flight loss of control. The pilot reported that the autopilot pitch trim ran away nose-down, and he was unable to disconnect the autopilot before losing control.
Examination Findings
Post-incident examination of the aircraft revealed that the left elevator horn was bent downward and the right elevator horn was broken off. The autopilot was tested; all disconnect functions operated properly except for the accelerometer test. The pitch trim board was found to be improperly installed in the autopilot and did not make connection. With the altitude hold engaged, the autopilot would hold the elevator position at the time of engagement and trim to keep forces neutral. If the aircraft slowed, it would lose altitude and trim nose-up.
Radar Data
Radar data showed the aircraft began to slow, then descended from 8,500 to 8,300 feet, climbed to 8,900 feet, and then descended very rapidly to 1,700 feet before a recovery was made.
Pilot Actions
According to reports, the pilot did not test the autopilot before takeoff.