NTSB Identification: IAD05LA138.
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Accident occurred Monday, September 12, 2005 in Rangeley, ME
Probable Cause Approval Date: 03/26/2007
Aircraft: Piper PA-46-500TP, registration: N747AW
Injuries: 3 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

With the autopilot engaged, and while climbing through approximately 5,000 feet msl, the pilot moved the heading bug 30 degrees to the right. The airplane then "sort of snapped with significant yaw," into a 60-degree right bank and lost about 1,800 feet of altitude. After recovering, the pilot continued to his destination. Examination of the airplane revealed that it was substantially damaged. Approximately five months prior to the accident, the autopilot system had been installed. Following the installation, the pilot experienced operational problems that included a "yaw problem" which began to worsen, but could not be duplicated by maintenance personnel. A postaccident examination of the autopilot and heading system also revealed no anomalies. Examination of the aft fuselage and tailcone revealed that the yaw damper was contaminated with oil. The source of the oil was an oil streak that ran from under the engine cowling aft along the belly of the airplane, and then up through the air conditioning exhaust vent. Two other airplanes which experienced yaw damper events were also examined, and oil contamination of the yaw damper amplifiers were identified.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A malfunction of the yaw damper system due to fluid contamination. Factors in the accident were the air condition exhaust vent design and the design stress limits of the airplane were exceeded.

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