What happened
During the cruise phase of flight, the pilot reported that the engine abruptly lost all power. Following this loss of power, the aircraft attempted a forced landing at night. During the maneuver, the aircraft collided with trees, which caused both wings to be torn off.
The investigation
An examination of the engine revealed that the crankshaft gear bolt was loose and the gear alignment dowel had been sheared. This condition resulted in a loss of continuity within the engine gear train. A metallurgical examination determined that the dowel pin failed due to fatigue.
Further investigation included interviews with the operator's mechanic, who stated that the engine had experienced a sudden stoppage caused by a propeller strike approximately 151 operating hours prior to the accident. Lycoming Service Bulletin #465 mandates specific inspection, modification, and assembly procedures for the crank gear following a propeller strike or any gear train repair. The mechanic confirmed that the requirements of this service bulletin were not performed after the previous propeller strike.