NTSB Identification: SEA90LA010.
The docket is stored on NTSB microfiche number 42196.
Accident occurred Friday, October 27, 1989 in NEAH BAY, WA
Probable Cause Approval Date: 10/07/1992
Aircraft: HUGHES 369D, registration: N9163F
Injuries: 1 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 AN EXTERNAL LOAD OPERATION, THE PILOT HAD JUST RELEASED THE LOAD AND WAS TRANSITIONING TO A CLIMB ATTITUDE WHEN THE TAIL ROTOR GEARBOX SEPARATED FROM THE TAIL BOOM. THE PILOT WAS UNABLE TO MAINTAIN CONTROL AND THE HELICOPTER COLLIDED INTO THE ROUGH TERRAIN. THE GEARBOX WAS METALLURGICALLY EXAMINED, REVEALING THAT ALL FOUR ATTACHMENT STUDS HAD FAILED DUE TO FATIGUE. FURTHER EXAMINATION REVEALED CONTAMINANTS ON THE GEARBOX MOUNTING PADS BETWEEN THE TAIL ROTOR GEARBOX AND THE TAIL BOOM; FRETTING WAS NOTED. AD88-17-09 AND SERVICE INFORMATION NOTICE DN-151/EN-39/FN-28 BOTH MANDATE INITIAL AND RECURRENT INSPECTION (EVERY FLIGHT) OF THE GEARBOX ATTACHMENT AREA.

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

FATIGUE FAILURE OF ALL FOUR ATTACHMENT STUDS OF THE TAILROTOR GEARBOX RESULTING IN SEPARATION OF THE GEAR BOX, AND INADEQUATE MAINTENANCE INSPECTION.

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