NTSB Identification: SEA92LA196.
The docket is stored on NTSB microfiche number 47819.
Accident occurred Sunday, September 06, 1992 in COKEVILLE, WY
Probable Cause Approval Date: 09/14/1993
Aircraft: PIPER PA-12, registration: N78599
Injuries: 2 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 PILOT OF THE PIPER PA 12 REALIZED THAT HE WAS EXPERIENCING A POWER LOSS WHILE MANEUVERING, LOOKING FOR MISSING SHEEP. HE TURNED TO LOWER, FLATTER TERRAIN. THE ENGINE CONTINUED TO LOSE POWER, SO HE MADE A FORCED LANDING IN UNSUITABLE TERRAIN. THE AIRCRAFT NOSED OVER AFTER TOUCHING DOWN. METALLURGICAL TESTING REVEALED THAT THE CRANKSHAFT HAD EXPERIENCED FATIGUE FAILURE. THE ENGINE HAD BEEN INSTALLED ON A FIELD APPROVAL. THE PROPELLER/ENGINE COMBINATION INSTALLED IN THIS AIRCRAFT HAD NOT BEEN TESTED OR APPROVED FOR THIS, OR ANY OTHER, INSTALLATION.

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

FATIGUE FAILURE OF THE CRANKSHAFT. FACTORS INCLUDE NON SUITABLE TERRAIN FOR A FORCED LANDING AND AN IMPROPER PROPELLER.

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