Accident Overview
A pilot flying a Piper PA-12 encountered a loss of engine power while maneuvering in an effort to locate missing sheep. The pilot initiated a turn toward lower, flatter terrain in an attempt to manage the situation. Despite this, the engine continued to lose power, necessitating a forced landing in terrain that was not suitable for a safe touchdown. After the aircraft touched down, it nosed over.
Findings
Post-accident metallurgical testing of the engine identified that the crankshaft had failed due to fatigue. The engine had been installed on the aircraft under a field approval. Furthermore, the combination of propeller and engine installed in this aircraft had not been tested or approved for this installation—nor had it been approved for any other installation.
Investigation
The investigation focused on the mechanical failure of the crankshaft. The presence of a field approval for the engine installation indicated that the modification did not follow standard certification processes. The lack of testing or approval for the propeller/engine combination raised questions about the compatibility and reliability of the powerplant configuration. However, no additional analysis or causal conclusions were drawn beyond the stated facts.