NTSB Identification: DEN91LA095.
The docket is stored on NTSB microfiche number 44402.
Accident occurred Monday, July 01, 1991 in GRAND JUNCTION, CO
Probable Cause Approval Date: 02/08/1993
Aircraft: BELL 412, registration: N20703
Injuries: 3 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.

DURING CRUISE FLIGHT, THE ENGINE TO TRANSMISSION DRIVE SHAFT FORWARD COUPLING OVERHEATED AND FAILED. THE PILOT EXECUTE AN AUTORATATION. DURING THE LANDING FLARE, THE PILOT DID NOT MAINTAIN ADEQUATE ROTOR RPM AND THE HELICOPTER LANDED HARD RESULTING IN SKID COLLAPSE. COMPANY MAINTENANCE PERSONNEL DISPATCHED THE HELICOPTER WITH A KNOWN DRIVE SHAFT COUPLING GREASE LEAK WHICH THEY HAD ATTEMPTED TO STOP BY USING AN UNAPPROVED SILICON SEALANT. THEY HAD REPACKED THE 500 PLUS HOUR COUPLING TWO TIMES PRIOR TO THE ACCIDENT. THE NORMAL REPACK INTERVAL WAS ONCE EVERY 600 HOURS. EXAMINATION OF THE FAILED DRIVE SHAFT DID NOT REVEAL ANY MISALIGNMENT, BUT DID ISOLATE HEAT RELATED FAILURE AREAS OF THE FORWARD COUPLING END.

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

THE PILOT'S FAILURE TO MAINTAIN ADEQUATE MAIN ROTOR RPM PRIOR TO TOUCHDOWN. FACTORS WERE: THE DISCONNECTED ENGINE TO TRANSMISSION DRIVE SHAFT AND THE INADEQUATE INSPECTION BY COMPANY MAINTENANCE PERSONNEL.

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