Accident Details
During cruise flight, the forward coupling of the engine-to-transmission drive shaft overheated and failed. The pilot performed an autorotation. During the landing flare, the pilot did not maintain adequate rotor RPM, causing a hard landing that resulted in the collapse of the skid.
Maintenance History
Company maintenance personnel dispatched the helicopter with a known drive shaft coupling grease leak. They had attempted to stop the leak by applying an unapproved silicon sealant. Prior to the accident, they had repacked the coupling twice; the coupling had accumulated over 500 hours in service. The normal repack interval was once every 600 hours.
Examination Findings
Examination of the failed drive shaft did not reveal any misalignment. However, investigators isolated areas of heat-related failure on the forward end of the coupling.