NUNAVAUGALUK LK, AK, USA
N8697F
HUGHES 369D
SHORTLY AFTER TAKEOFF, AT 1,000 FT AGL, THE PILOT EXPERIENCED AIRFRAME VIBRATION AND A GRINDING SOUND. HE ENTERED AUTOROTATION, AND AT 200 FT AGL THE TAIL ROTOR AND PART OF THE T/R GEAR BOX SEPARATED FROM THE HELICOPTER. IT THEN ROTATED APPROXIMATELY 720 DEG AND IMPACTED THE GROUND. ONE OF THE T/R BLADES WAS MISSING THE ABRASION STRIP. AN AIRWORTHINESS DIRECTIVE (AD) & SERVICE BULLETIN (SB) WERE IN EFFECT DIRECTING INSTALLATION OF RIVETS WITHIN 300 HRS TO PREVENT POSSIBLE LOSS OF TAILROTOR CONTROL. DUE TO SEASONAL USE, HELICOPTER HAD LESS THAN 160 HRS SINCE ISSUANCE OF THE AD. TAIL ROTOR BLADE FOUND INTACT WAS 40% DEBONDED, BUT WOULD PASS A 'TAP TEST' IAW MANUFACTURER'S SB. FAILED BLADE ESTIMATED TO BE 90% DEBONDED. DAILY VISUAL INSPECTION REQUIRED BY SB REPORTEDLY DID NOT DETECT DEBONDING IN PROGRESS.
THE SEPARATION OF THE TAIL ROTOR ABRASION STRIP AND THE SUBSEQUENT TOTAL LOSS OF THE TAIL ROTOR. FACTORS CONTRIBUTING TO THE ACCIDENT WERE: INSUFFICIENT MANUFACTURER'S MAINTENANCE DESIGN CHANGES, INADEQUATE AIRCRAFT EQUIPMENT DESIGN BY THE MANUFACTURER AND INSUFFICIENT STANDARDS OF THE FAA CERTIFICATION ORGANIZATION.
Source: NTSB Aviation Accident Database
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