Incident Summary
A pilot reported engine failure during cruise flight at 11,500 feet mean sea level over terrain at 10,000 feet. The aircraft sustained damage during a forced landing on a rocky ridgeline. The airplane came to rest inverted after a rock struck during the landing roll.
Pilot Report
The pilot stated that the oil pressure gauge indicated zero while cruising. Approximately five minutes later, the engine produced a clanking sound and began to break apart internally. Within a few additional minutes, the engine seized completely. The pilot executed a forced landing between trees on a rocky ridge top. During the landing roll, the airplane hit a rock and nosed over, ending up inverted.
Postcrash Examination
Examination of the engine after the accident revealed extensive internal damage. Components were sent to a metallurgical laboratory for analysis. The investigation determined that the number one piston had developed in-service fatigue cracks. These cracks led to the disintegration of the piston, which in turn caused the general failure of the engine.