Incident Overview
The airplane sustained impact and fire damage when it cartwheeled during a forced landing following a loss of engine power. According to the pilot, approximately 30 minutes into the flight, he heard a "clunk," after which the engine stopped running and the propeller was not windmilling. The pilot attempted to restart the engine without success. During an off-airport landing attempt in a bean field, the right wing contacted the ground, causing the airplane to cartwheel, and a post-impact fire ensued.
Engine Examination
Inspection of the engine revealed that the piston and piston pin on the number 4 cylinder were separated from the connecting rod. A metallurgical examination of the number 4 connecting rod determined that the piston pin end of the rod was fractured and the fractured ends were deformed inward. The fractured surface exhibited an area typical of a fatigue crack that originated at the forging parting plane on the exterior surface. The fatigue origin areas contained ratchet marks, indicating that fatigue cracking initiated at multiple sites and extended through approximately 60% of the wall thickness.
Maintenance History
The engine, a Lycoming O-320-E2D, was overhauled on August 11, 2003, at an engine total time of 3,918.7 hours. The engine had accumulated approximately 70 hours since the overhaul. Maintenance records indicate that during the overhaul, the connecting rods were magnafluxed, rebushed, checked for alignment, and reinstalled. The connecting rods were the original engine rods.