Night Forced Landing After Engine Crankshaft Fatigue Crack Causes Oil Loss and Propeller Separation (N3707Z)

Incident Details

During a night cross-country flight, the pilot observed engine oil appearing on the windows. Unable to reach an airport before the oil pressure reached zero, the pilot experienced engine vibration and then the propeller separated from the engine. With forward visibility compromised and limited side visibility, the pilot executed a forced landing on a highway service road. During the landing roll, the airplane struck highway signs and reflectors. The pilot reported a fire on the highway behind the airplane, but it did not reach the aircraft.

Investigation Findings

A teardown examination of the engine revealed a failure of the crankshaft that was initiated by a pre-existing fatigue crack. Evidence indicated that the opening of this fatigue crack led to a gradual loss of lubricating oil, which subsequently resulted in the separation of the propeller.