On June 8, 2000, at 1545 central daylight time, a Piper PA-28-161, N8189T, piloted by a certified flight instructor, sustained substantial damage during an in-flight collision with a swamp, during a forced landing following a loss of engine power while on initial climb from runway 18 (2,691 feet by 75 feet, dry/asphalt) at the Flying Cloud Airport, Minneapolis, Minnesota. The airplane was owned and operated by Thunderbird Aircraft Company, Minneapolis, Minnesota. Visual metrological conditions prevailed at the time of the accident. The flight was operating under the provisions of 14 CFR Part 91 and was not on a flight plan. The certified flight instructor and single dual student reported minor injuries. The local instructional flight was departing at the time of the accident.

According to the dual student's written statement, "At 1200 ft. [feet] there was one big bang, one puff of black smoke. The prop [propeller] stopped dead. At that point the flight instructor ... [omitted name] took over, radio to the tower we lost our engine and we were going down. She [the flight instructor] turned back towards the airport but there was a hill we couldn't clear so she kept turning. As we made almost a 360[degree] turn we started clipping the tree tops. I saw a wing shear off, then [I] was knocked out."

The NTSB Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2, stated that the flight instructor had no recollection of the accident or the events leading to the accident.

Post-accident investigation revealed that the engine crankshaft had failed during flight. The two pieces of the broken crankshaft with attached connecting rods and main bearings were shipped to the Materials Laboratory Division of the National Transportation Safety Board (NTSB), Washington, D.C., for further evaluation.

According to the NTSB Materials Laboratory Factual Report, the crankshaft separated in the cheek between the number three bearing journal and the number three connecting rod journal. The factual report further noted that the number three and four connecting rods were bent. The factual report indicated that 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 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 stated, "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 stated, "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 complete Materials Laboratory Factual Report is appended to this factual report.

The crankshaft (Part number LW17020, serial Number S93324-1) had been inspected as part of an engine overhaul on November 25, 1997. The service release tag for the crankshaft stated, "Magnafluxed, Inspected, Polished Rods and Mains M-003, Cadmium Plated and Baked Flange".

A copy of the service release tag is appended to this factual report.

The crankshaft was reinstalled into a Lycoming O-320-D3G engine, serial number L-13305-39A, and an airworthiness logbook entry was made on January 15, 1998. The last maintenance recorded for the engine was on June 6, 2000, and the engine had accumulated a total time of 5,487 hours, 1,281 hours since major overhaul.

Copies of the engine logbook entries from the time of the last major overhaul are attached this factual report.

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