NTSB Identification: SEA98LA192.
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Accident occurred Wednesday, September 30, 1998 in AVON, MT
Probable Cause Approval Date: 01/11/2000
Aircraft: Mayala DRAGONFLY, registration: N4478V
Injuries: 1 Minor.

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 pilot-in-command/owner of the homebuilt Volkswagen-engine powered Dragonfly departed Helena, Montana, uneventfully. After approximately 30 minutes of flight he observed the engine oil pressure decrease to zero in less than two minutes with a concurrent increase in oil temperature. He then executed a forced landing in a rough pasture during which the aircraft bounced and then cartwheeled. Post-crash examination revealed oil on the aircraft's firewall and underside. Further examination revealed that the engine rear crankshaft seal was deformed and the neoprene gasket was missing.

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

Failure of the engine crankshaft aft oil seal resulting in the loss of engine oil, and rough terrain during the forced landing.

Full narrative available

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