On October 20, 1991, a North American NAVION D (registration N10JF) operated by Rempert, Roger L. was involved in an aviation accident near Lake Geneva, WI. Investigators recorded the probable cause as: A broken crankshaft due to fatigue failure emanating from a scratch in the fillet at the number 2 main bearing journal. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A Cessna 172M experienced an in-flight engine failure caused by a fractured crankshaft, resulting in a forced landing in a field. Investigation revealed fatigue cracks originating from a scratch on the main bearing journal.
What happened
The pilot climbed to cruise altitude and set the engine power before the aircraft's engine began to vibrate briefly and then quit. Following the sudden loss of power, the pilot executed a forced landing in a rough field.
The investigation
A teardown of the engine revealed that the crankshaft was broken. Examination of the fracture surface indicated that the failure originated from fatigue cracks emanating from a scratch located in a fillet at the number 2 main bearing journal.
Findings
The mechanical failure was traced to material fatigue initiated by a pre-existing defect. The presence of the scratch on the critical bearing surface served as the stress concentration point for the crack propagation that ultimately led to the catastrophic breakage of the crankshaft during operation.
Probable cause
A broken crankshaft due to fatigue failure emanating from a scratch in the fillet at the number 2 main bearing journal.
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