NTSB Factual Report

On August 12, 2001, at 1530 central daylight time, a Piper PA-28-180, N8424W, experienced a total gear collapse during a forced landing in a plowed field in Union, Illinois. The pilot performed the off airport landing after the propeller separated from the engine during the flight. The pilot and two passengers were not injured. A third passenger received a minor injury. The airplane was substantially damaged. The 14 CFR Part 91 local flight was operating in visual meteorological conditions without a flight plan. The flight originated from the Lake in the Hills Airport, Lake in the Hills, Illinois, at 1445 central daylight time.

The pilot reported that approximately 45 minutes after takeoff, while in cruise flight, the crankshaft broke and the propeller separated from the engine. He reported that the windscreen was sprayed with oil and the engine seized. The pilot reported that he was at an altitude of approximately 4,000 feet above sea level when the engine seized. He reported that he proceeded to make a forced landing at a sod farm. The pilot reported the field was being prepared for planting and the recently tilled soil was very soft. Upon touching down, the landing gear stuck in the ground and it separated from the airplane. The pilot reported that the airplane slid approximately 50 feet during which time the right wing twisted.

The separated portion of the propeller was not located. The crankshaft was removed from the engine and sent to the NTSB Materials Laboratory in Washington DC, for examination. This examination revealed the crankshaft was separated at the No. 1 main bearing area. The fracture was on multiple planes. The spiral plane extended from the oil transfer tube. A crack on the spiral plane extended aft into the forward crank cheek for the No. 1 cylinder. Examination of the crack showed fatigue bands on the spiral crack, that initiated in the vicinity of the oil transfer tube hole, and propagated along the entire length of the crack. The fatigue crack initiated at the bore surface of the hole approximately midway between the exterior and interior surfaces of the crankshaft wall. The crack contained what appeared to be a large ratchet mark that extended from the bore surface of the hole.

According to the pilot, the airplane was involved in a propeller strike in March 1999. The engine logbook indicates that on March 18, 1999, the engine was removed for a tear down inspection because of a propeller strike. A work order parts list dated June 4, 1999, shows that the insurance company supplied a replacement crankshaft. A Serviceable Tag for the crankshaft shows that it was overhauled sometime between December 8, 1998 and February 12, 1999. The engine was reinstalled on N8424W on July 14, 1999.

NTSB Probable Cause

The total failure of the crankshaft as a result of fatigue and the unsuitable terrain encountered during the forced landing. Factors associated with the accident were the soft terrain on which the forced landing was made and the subsequent gear collapse.