Primary finding
Probable cause
Fatigue failure of the crankshaft. Factors include non suitable terrain for a forced landing and an improper propeller.
Investigator assessment
Analysis 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.
Source record
Factual narrative
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