NTSB Identification: CHI00LA154.
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Accident occurred Thursday, June 08, 2000 in MINNEAPOLIS, MN
Probable Cause Approval Date: 10/02/2001
Aircraft: Piper PA-28-161, registration: N8189T
Injuries: 2 Minor.
NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
During initial climb after takeoff the engine crankshaft failed, resulting in a engine failure. The flight instructor took control of the aircraft and executed a forced landing into a swamp. Post-accident investigation revealed that the engine crankshaft had failed between the number three bearing journal and the number three connecting rod journal. According to the National Transportation Safety Board Materials Laboratory Factual Report, the fracture surface, on the forward piece of the crankshaft, "...appeared relatively smooth with curving crack arrest lines, features typical of fatigue." The report stated, "Fracture features for the fatigue region emanated from an origin...at the surface of the aft radius of the third main journal...." The factual report indicated that the fatigue cracking progressed through more than 80-percent of the check prior to the final separation. The factual report further added that that the inner and outer diameter surfaces of the number three main bearing halves were circumferentially rubbed. The report states, "One edge of each of these bearing halves was rubbed and worn in the approximate shape of the journal radius. In addition, the antirotation tabs for these bearing halves were worn away from the outside diameter surface." The factual report indicated that the number four main bearing halves were deformed and the inner diameter surface was gouged. The report states, "Also, some slight circumferential rubbing marks were observed on the inner diameter surface of the number 1 and 2 main bearing halves. No evidence of heat tinting was noted on any of the bearing halves."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the failure of the engine and the unsuitable terrain for landing encountered by the pilot-in-command. Factors to the accident were the fracture of the crankshaft due to fatigue, excessive main bearing wear, and the swampy terrain condition. Full narrative available
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