On June 19, 1996, a Hughes 269C (registration N7400F) operated by Olympic Air, Inc. was involved in an aviation accident near Eldon, WA. Investigators recorded the probable cause as: Failure of the number two connecting rod assembly due to fatigue of the rod cap and overload of the bolts, associated with fretting between the rod cap inner face and bearing surface. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 2 related events involving the same aircraft type or operator are linked below.
A rotorcraft experienced shaking and a pop during cruise over Hood Canal, prompting an intentional ditching. The pilot could not swim ashore; the passenger survived. Examination found a connecting rod failure due to fatigue.
Incident Overview
While in cruise flight over Hood Canal, the rotorcraft began shaking. A ground witness reported hearing a 'pop' and observed white smoke. The pilot-in-command executed an intentional ditching. The pilot was unable to swim to shore, and the passenger survived.
Examination Findings
Postcrash examination of the rotorcraft revealed that the Lycoming HIO-360-D1A engine's number two connecting rod assembly had failed. The failure occurred when the cap end separated. Metallurgical examination determined that the connecting rod cap had failed from fatigue, and both connecting rod bolts had failed in overload. The fatigue was associated with fretting within the rod cap inner face between the face and the bearing surface.
Probable cause
Failure of the number two connecting rod assembly due to fatigue of the rod cap and overload of the bolts, associated with fretting between the rod cap inner face and bearing surface.