What happened
During the final approach, the engine of the aircraft failed without warning. This loss of power forced the pilot to execute a forced landing into a bird sanctuary characterized by heavy woods.
The investigation
An examination of the engine identified that the crankshaft gear attachment bolt was loose, exhibiting 0.196 inches of play. Additionally, the dowel pin was found to be sheared. According to gear installation instructions, the gear must be seated using a drift and hammer to ensure no more than 0.001 inches of clearance; failure to meet this specification causes the dowel pin to become offset and work. Investigators found evidence that both the bolt and the dowel pin had been working.
The shearing of the crankshaft dowel pin allowed the gear to rotate around the bolt, which disconnected the gear and the idler gears responsible for transmitting torque to the magnetos. Secondary damage was also noted in the left magneto. Maintenance records showed that the engine had undergone an overhaul 88.7 hours prior to the accident.