The pilot stated that shortly after takeoff on the skydiving flight, the airplane’s engine made a “clicking”
sound and lost power. The pilot subsequently performed a forced landing to a field, during which the
airplane flipped over and sustained substantial damage to the fuselage, right wing, and tail. Examination
of the engine revealed the crankcase web mating surfaces at the Nos. 2, 3, and 4 bearing saddles
exhibited pitting consistent with fretting, which was indicative of improper preloading (torque) of the
through bolts. Additionally, the No. 2 main bearing was displaced from its saddle and severely worn,
and the crankshaft fractured due to fatigue. A review of maintenance records revealed the engine’s
camshaft and lifters were replaced about 280 hours before the accident; this was the last documented
time during which the applicable through bolts and associated nuts would have been assembled. Given
this information, it is likely that maintenance personnel failed to properly apply torque to these through
bolts during this maintenance, which ultimately resulted in the crankshaft failure and the subsequent loss
of engine power.
DiverDriver.com