Incident Overview
On approach to the runway, the pilot-in-command reported a power loss. The aircraft subsequently passed through the tops of trees approximately 150 feet beyond the point of power loss, entered a stall/spin maneuver, and impacted a power line and the ground roughly 2,800 feet short of the runway threshold. Post-impact examination found the flaps and landing gear in a retracted position.
Engine Examination
Post-crash examination of the engine revealed that the crankshaft had separated in fatigue. The fatigue crack originated from a circumferential gouge mark on the aft face of the #2 cheek, located outboard of the forward radius of the #1 rod journal. This gouge mark was consistent with the connecting rod shifting forward during engine operation. Rub marks on the cheek walls of the #1 connecting rod were consistent with tight piston pin bushing-to-piston pin clearance. Additionally, all connecting rod bushings were found to be undersize.
Maintenance History
Review of the airframe and engine logs showed that a top overhaul of the engine had been performed approximately 23 flight hours prior to the crankshaft failure. During that overhaul, the piston pins were replaced, but the connecting rod bushings were not. No dimensional check of the bushings was made at that time, nor was one required. The engine had been overhauled 515 hours before the top overhaul. The manufacturer's overhaul manual specifies that new bushings should be reamed to the specified inside diameter.
Additional Findings
Post-crash examination also identified non-standard connecting rod cotter keys and light fretting between the engine case halves.
Probable Cause
The probable cause of the incident is the fatigue separation of the crankshaft due to a circumferential gouge mark on the #2 cheek, consistent with shifting of the connecting rod. Contributing factors include undersized connecting rod bushings and the lack of dimensional verification during the top overhaul.