Accident Sequence
During cruise flight, the helicopter experienced a sudden and severe right yaw. The pilot initiated an autorotation and ditched the helicopter in rough water. Touchdown occurred on top of a wave, after which the helicopter rolled over. Survivors did not deploy the life raft. Another helicopter arrived but could not land due to rough seas. A life raft was dropped, but by the time the copilot swam to it and inflated it, the raft had blown downwind. The copilot was unable to paddle against the wind to reach the other survivors. The helicopter sank before a rescue boat arrived, although it was later recovered.
Investigation
Examination of the helicopter revealed that the female portion of a tail rotor coupling, part number 204-040-604-5, had failed due to lack of lubrication. The proper type of lubricant had been used. The coupling seal, part number 204-040-611-1, showed tears and a circumferential cut measuring 0.14 to 0.16 inch long. Grease was found throughout the cut area. The helicopter had accumulated 1,226 hours total time and 376 hours since overhaul.
Findings
The investigation concluded that the tail rotor coupling failure resulted from insufficient lubrication. The seal damage likely allowed grease to escape, contributing to the lack of lubrication.