Accident Piper PA-12 N78599, Sunday 6 September 1992

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Date:	Sunday 6 September 1992
Time:	10:00 LT
Type:	Piper PA-12
Owner/operator:	John I Ritter
Registration:	N78599
MSN:	12-3961
Total airframe hrs:	4777 hours
Engine model:	Lycoming O-340-A1A
Fatalities:	Fatalities: 0 / Occupants: 2
Other fatalities:	0
Aircraft damage:	Substantial
Category:	Accident
Location:	Cokeville, WY - United States of America
Phase:	Manoeuvring (airshow, firefighting, ag.ops.)
Nature:	Private
Departure airport:	Kemmerer, WY
Destination airport:
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
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.

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

Accident investigation: