On June 27, 1983, a Cessna T188C (registration N9639J) was involved in an aviation accident near Marshall, MO. Investigators recorded the probable cause as: Fatigue fracture of the crankshaft at the #3 main bearing journal. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An aircraft experienced an engine failure while en route to spray, jettisoned its load, and subsequently impacted trees in a wooded pasture. Metallurgical analysis revealed a fatigue fracture of the crankshaft.
Incident Summary
An agricultural aircraft experienced an engine failure while en route to a spraying operation. The aircraft was observed to jettison its load before impacting trees in a wooded pasture. No further details about the operation or pilot actions were provided in the source.
Metallurgical Examination Findings
A metallurgical examination of the engine revealed that the crankshaft, part number 631716, had fractured due to fatigue progression. The fatigue crack propagated through the forward cheek of the #3 main bearing journal. Initiation of the fatigue crack occurred at a location 0.047 inches below the forward radius surface. No metallurgical abnormalities were detected at the origin site of the fracture.
Probable cause
Fatigue fracture of the crankshaft at the #3 main bearing journal.
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