NTSB Identification: ANC96LA053.
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Accident occurred Saturday, April 20, 1996 in GRAYLING, AK
Probable Cause Approval Date: 02/01/1997
Aircraft: Maule M-5-210C, registration: N9704N
Injuries: 1 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.
The certificated private pilot departed a remote airstrip. About 1,000 feet above the ground, the engine quit. The pilot performed an emergency landing on soft snow covered terrain and the airplane nosed over. An engine examination revealed that the alternator drive coupling, consisting of a hub, retainer and bushing, fragmented within the engine. The alternator drive shaft and the oil pump gear were fractured when fragments of the retainer were enmeshed in the engine accessory gear teeth that drove both accessories. The number 6 cylinder connecting rod failed and penetrated the engine case due to a lack of lubrication. The engine, including the alternator, was overhauled 250 hours before the accident. An engine manufacturer's service bulletin recommended inspection and replacement of the standard alternator drive coupling every 500 hours. The engine manufacturer offered a one piece alternator drive coupling in which the retainer, bushing and hub were bonded together as one unit.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: disintegration of the alternator drive coupling, jamming of the accessory drive gear, shearing of the oil pump drive, oil starvation, and failure of the number 6 cylinder connecting rod. Non-compliance with a manufacturer's service bulletin and soft snow were factors in the accident. Full narrative available
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