Primary finding
Probable cause
The pilot's inadvertent stall and descent into terrain during a forced landing. Related factors are the manufacturer's undertorqued crankcase halves and inadequate surveillance, the pilot's delay in setting up the proper descent rate, and the altered aircraft performance with the separated propeller assembly.
Investigator assessment
Analysis narrative
The pilot reported a loss of engine power and declared an emergency. ATC issued vectors to the nearest airport, which was about ten miles away. The pilot then advised ATC he lost the propeller. About 3 minutes after the emergency was declared, the pilot reported 'i have the field....don't think i'm going to make it.' the airplane impacted terrain about 1.5 miles east of the airport. Post-accident investigation revealed the crankshaft was separated in two locations and the no. 2 main bearing had shifted in the journal. Metallurgical examination revealed one fracture was determined to be due to overstress and excessive torsional loads. The other fracture '...contained a well defined crack arrest pattern indicative of a high cycle fatigue crack. Examination of the crankcase halves revealed evidence of fretting at the mating surfaces.
Source record
Factual narrative
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