Incident Overview
While climbing through approximately 5,000 feet mean sea level with the autopilot engaged, the pilot adjusted the heading bug 30 degrees to the right. The aircraft then experienced a sudden yaw and rolled into a 60-degree right bank, losing about 1,800 feet of altitude. The pilot regained control and continued to the intended destination. Following the flight, examination revealed substantial damage to the airplane.
Autopilot System History
The autopilot system had been installed approximately five months prior to the incident. After installation, the pilot reported operational issues, including a yaw problem that progressively worsened. However, maintenance personnel were unable to reproduce the problem during troubleshooting.
Postaccident Examination
A postaccident inspection of the autopilot and heading system found no anomalies. However, examination of the aft fuselage and tailcone revealed that the yaw damper was contaminated with oil. The oil originated from a streak running from under the engine cowling along the belly of the aircraft, then up through the air conditioning exhaust vent.
Additional Findings
Two other aircraft that had experienced yaw damper events were also examined. In those cases, oil contamination of the yaw damper amplifiers was identified.