What happened
On September 6, 2010, a Cessna P210N, registration N4632A, experienced a loss of engine power while performing an instrument proficiency check near Caledonia, Michigan. The flight, operated by Centurion Aviation LLC, departed from Gerald R. Ford International Airport (GRR) at approximately 0800.
While the crew was executing a holding pattern at 4,000 feet, the pilot heard a loud bang from the engine area. The pilot removed his view limiting devices and turned the aircraft toward GRR. The crew determined that the engine had lost power and prepared for an off-field landing in an alfalfa field. During the approach, the aircraft impacted terrain at the base of a hill, causing the nose gear to separate. The aircraft then slid into a corn field, where fuel from the left wing tip tanks leaked and ignited, resulting in a post-impact fire. Both the pilot and the flight instructor were not injured.
The investigation
FAA inspectors found no anomalies in the airframe prior to impact. The engine, a Teledyne Continental TSIO-520-RCAF, was sent to the manufacturer for a teardown.
Investigators discovered that the crankshaft had experienced a separation of its number three short cheek. Metallurgical analysis confirmed the separation was consistent with fatigue. The investigation also revealed that the number two lower through-bolt had the lowest torque value of all through-bolts examined. Furthermore, a nut intended for a cylinder stud had been incorrectly installed on that through-bolt. Fretting was noted on the mating surfaces of the main bearing supports near this bolt, and the associated bearing had spun out of its support.