What happened
The aircraft impacted a line of trees located short of the runway shortly after the engine ceased operation while on final approach for landing. The sudden loss of power during this critical phase of flight resulted in the crash.
The investigation
A teardown of the failed engine revealed significant internal damage to the crankshaft gear retention system. Specifically, the crankshaft gear bolt had backed out, and the head of the bolt was found to have contacted the oil pump drive tank. Additionally, evidence indicated that foreign material had passed through the gear system. This debris originated from severely spalled tappets. The crankshaft gear dowel pin was found sheared, and several camshaft lobes exhibited wear consistent with corresponding tappet face spalling.
Findings
The failure mode was attributed to the internal failure of the crankshaft gear retention system. While the mechanical evidence points to a cascade of failures involving the bolt, dowel pin, and foreign object debris from spalled components, the initial source of this failure mode could not be determined.