NTSB Identification: SEA96LA219.
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Accident occurred Monday, September 23, 1996 in TROY, MT
Probable Cause Approval Date: 08/21/1997
Aircraft: Kaman HH-43 B/F, registration: N4069R
Injuries: 2 Minor,4 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that while in cruise flight, the internal autorotation cockpit gauge needles split, and the helicopter lost altitude. The rotor rpm was decreasing, and the pilot initiated an autorotation. During the descent, the pilot noted that the N1 gauge indicated that the engine was running, but there was no power to the rotor. The helicopter landed hard, which drove the landing gear through the belly and separated the tail boom. A postaccident investigation revealed that bearings in the one-way freewheeling sprag clutch had failed. The one-way clutch was not a time-retireable item, and determining total time of the assembly from the maintenance records was not possible.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

failure of the freewheeling sprag unit bearings for undetermined reasons.

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