Accident Description
While on final approach, the aircraft's engine failed without any prior warning. The pilot was forced to execute a forced landing into a heavily wooded bird sanctuary.
Examination Findings
Post-accident examination of the engine disclosed that the crankshaft gear attachment bolt was loose, exhibiting 0.196 inches of play. The accompanying dowel pin had sheared. According to the gear installation instructions, the gear was to be seated with a drift and hammer, allowing no more than 0.001 inches of clearance. If this clearance is exceeded, the dowel pin would become offset and work. Evidence of working was present on both the bolt and the dowel pin. The shearing of the crankshaft dowel pin would have released the gear to rotate about the bolt, thereby disconnecting the gear from the idler gears that transmit torque to the magnetos. This disruption prevented the magnetos from receiving power, resulting in the loss of engine ignition. Secondary damage was observed on the left magneto.
Maintenance Records
The engine's maintenance records indicated that it had been overhauled 88.7 hours prior to the accident.