Accident Overview
A US Navy aircraft, flown by a Navy aviator with another Navy aviator in the right front seat, crashed during a mission over mountainous terrain. The accident occurred after the engine sustained a catastrophic crankshaft failure.
Sequence of Events
While over mountainous terrain, the engine experienced a catastrophic crankshaft failure. Despite the availability of lower and more suitable emergency landing areas, the pilot elected to proceed towards higher terrain. Internal communications between the right-seat occupant—a more experienced pilot—and the pilot-in-command indicated a plan to stall the airplane prior to landing on an upward sloping mountain ridge. The pilot subsequently misjudged the altitude and stalled the airplane. Both pilots were killed.
Investigation Findings
The investigation determined that the crankshaft failure was caused by inadequate torque of the through bolts, which led to fretting and galling on the crankcase halves. At the time of failure, the engine had accrued 618 hours since major overhaul and had experienced seven vacuum pump failures due to misalignment of the crankshaft drive gear. Additionally, the through bolts were removed by the operator to repair the No. 3 Rosan stud 322 hours before the crankshaft failed.