Primary finding
Probable cause
The failure of the alternator drive coupling, and debris from the failed coupling that lodged in the engine oil pump, resulting in a sheared oil pump drive shaft. The engine subsequently failed because of oil starvation.
Investigator assessment
Analysis narrative
While en route to his destination airport, the pilot experienced complete loss of engine power. The pilot selected a pasture and made an emergency landing. During the rollout, the airplane collided with trees along a fence line. Examination of the engine disclosed that the alternator drive coupling failed, and debris from the coupling lodged in the engine oil pump drive; the engine experienced a loss of engine oil pressure.
Source record
Factual narrative
On August 19, 1994, at 1740 central daylight time, a Cessna, N9797V, collided with trees while attempting an emergency landing in a pasture near Clarksburg, Tennessee. The business flight operated under the provisions of 14 CFR Part 91 with a visual flight plan filed. Visual weather conditions prevailed at the time of the accident. The aircraft received substantial damage, the pilot was not injured. The flight departed Nashville, Tennessee, at 1640 hours. According to the pilot, while flying at 2500 feet enroute to his destination airport, the engine sputtered twice and lost power. After the second occurrence, the pilot selected a pasture for an emergency landing. During the landing rollout, the airplane collided with a fence and trees. The engine examination revealed that the engine sustained oil starvation damage. Steel and rubber debris from internal engine components were recovered from the engine oil sump. The examination also revealed that the alternator drive gear had sheared and was lodged in the accessary pad opening; the engine oil pump drive shaft had also sheared (see attached inspector's statement). -