Accident Description
A certificated private pilot departed from a remote airstrip. After climbing to approximately 1,000 feet above ground level, the engine lost power. The pilot executed an emergency landing on terrain covered with soft snow. During the landing, the airplane nosed over. The extent of damage to the aircraft was not specified.
Engine Examination
Post-accident examination of the engine revealed that the alternator drive coupling, which consisted of a hub, retainer, and bushing, had fragmented internally. Fragments of the retainer became enmeshed in the engine accessory gear teeth, causing fractures to both the alternator drive shaft and the oil pump gear. Additionally, the number 6 cylinder connecting rod failed and penetrated the engine case; this failure was attributed to a lack of lubrication.
Maintenance History
The engine, including the alternator, had undergone an overhaul 250 hours before the accident. A service bulletin issued by the engine manufacturer recommended inspection and replacement of the standard alternator drive coupling every 500 hours. The manufacturer also offered an alternative one-piece alternator drive coupling in which the retainer, bushing, and hub were bonded together as a single unit.