What happened
During cruise flight over Hood Canal, the rotorcraft began experiencing significant vibrations. A witness on the ground reported hearing a loud "pop" accompanied by the sight of white smoke emanating from the aircraft. In response to the mechanical failure, the pilot-in-command performed an intentional ditching in the water. While the passenger survived the impact, the pilot was unable to swim to shore and the accident resulted in 1 fatality.
The investigation
Postcrash examination of the Lycoming HIO-360-D1A engine identified that the number two connecting rod assembly had failed due to the separation of the cap end. A metallurgical analysis determined that the connecting rod cap failure was caused by fatigue. This fatigue was specifically associated with fretting occurring on the inner face of the rod cap, located between the face and the bearing surface. Additionally, investigators found that both connecting rod bolts had failed due to overload.