SPARKS, NV, USA
N100HH
HILLER UH12D
THE CERTIFICATED PRIVATE HELICOPTER PILOT, THE SOLE OCCUPANT, WAS ON A LOCAL AREA FLIGHT WHEN A STRONG, MEDIUM TO HIGH FREQUENCY VIBRATION DEVELOPED IN THE TAIL SECTION OF HIS HELICOPTER. THE PILOT ELECTED TO MAKE A PRECAUTIONARY LANDING IN AN OPEN DIRT AREA, AND EXECUTED AN AUTOROTATION. AFTER TOUCHDOWN THE HELICOPTER SLID ON ROUGH, ROCKY TERRAIN, CAUSING THE MAIN ROTOR BLADES TO CONTACT THE TAIL BOOM. THREE FEET OF THE TAIL BOOM INCLUDING THE TAIL ROTOR GEAR BOX AND BLADES, AND THE TAIL ROTOR DRIVE SHAFT WERE SEVERED. AN EXAMINATION OF THE TAIL ROTOR DRIVE SHAFT AT THE POSITION WHERE A SUPPORT BEARING IS MOUNTED, REVEALED SIGNS OF HEAT AND WEAR. DURING THE IMPACT SEQUENCE, THE DRIVE SHAFT SUPPORT BEARING DEPARTED THE HELICOPTER AND WAS NOT RECOVERED.
THE ENCOUNTER WITH ROUGH, UNSUITABLE TERRAIN DURING A PRECAUTIONARY LANDING. CONTRIBUTING TO THE ACCIDENT WAS THE PILOT'S DECISION TO MAKE AN AUTOROTATION AFTER ENCOUNTERING AN AIRFRAME VIBRATION.
Source: NTSB Aviation Accident Database
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