NEAH BAY, WA, USA
N9163F
HUGHES 369D
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.
FATIGUE FAILURE OF ALL FOUR ATTACHMENT STUDS OF THE TAILROTOR GEARBOX RESULTING IN SEPARATION OF THE GEAR BOX, AND INADEQUATE MAINTENANCE INSPECTION.
Source: NTSB Aviation Accident Database
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