Accident Description
The pilot reported that during cruise flight, she heard an abnormal loud knocking noise from the engine. Within seconds, the engine exploded, and a rush of oil from the engine compartment covered approximately 90 percent of the forward windscreen. The cabin filled with smoke from burnt oil, and the propeller stopped rotating. The pilot executed a forced landing onto a 2,000-foot-long airstrip. Upon touchdown, the aircraft overran the departure end of the runway and impacted a fence.
Aircraft and Maintenance History
The pilot had purchased the 1978 model airplane earlier in 2006 and possessed its maintenance records. The records indicated that the engine had received three field overhauls: in 1980, 1991, and 1994. At the time of the accident, the engine's total time was 5,538 hours, with 950 hours since the last overhaul.
Examination Findings
After the accident, examination of the engine revealed a catastrophic internal mechanical failure that resulted in a breach of the crankcase at the forward top section. The oil lines were found secure at their respective engine fittings. The crankshaft and respective connecting rods exhibited severe heat distress consistent with lubrication deprivation. The number 1, 2, and 4 connecting rods were displaced from their respective journals, while the number 3 connecting rod remained on the journal, which also showed severe heat distress. The crankshaft and camshaft remained intact. No anomalies were found with the accessory components and gears, or with the lubricating system. The specific event leading to the lubrication deprivation and heat distress was not identified.