Accident Summary
While climbing through an altitude of 6,000 feet, the pilot heard and felt a distinct thud. Immediately after the thud, the pilot realized that the engine had ceased to operate. In response to the engine failure, the pilot conducted an emergency landing. The aircraft touched down in a muddy corn field. During the landing, the nose gear became caught in the soft, wet soil, causing the aircraft to pitch forward and nose over.
Investigation Details
A thorough teardown of the engine was undertaken as part of the accident investigation. The teardown revealed that the engine's crankshaft had fractured. Specifically, the fracture was located through the short cheek, just aft of the number 2 bearing journal. This fracture was complete, separating the crankshaft into two pieces. A metallurgical examination of the fracture surfaces was performed. This examination focused on determining the mode of failure. The examination determined that the failure originated from high cycle fatigue. High cycle fatigue is a progressive damage mechanism caused by repeated stress cycles. The fatigue initiation occurred at the surface of the short cheek area, which is a region of stress concentration. The fatigue crack then propagated through the crankshaft until the remaining material could no longer support the load, resulting in final fracture.
Findings
The investigation determined that the engine failure was due to a crankshaft fracture caused by high cycle fatigue. The emergency landing was executed by the pilot, and the aircraft nosed over due to the soft ground conditions.