AIKEN, SC, USA
N118HS
BELL UH-1E
THE HELICOPTER WAS BEING OPERD AT APRX 100 FT AGL WITH A HOPPER EXTDD FROM A CABLE. WITNESSES HEARD A LOUD POPPING SOUND. AS THEY LOOKED IN THE DRCTN OF THE HELICOPTER, THEY NOTED THE TAIL ROTOR WAS NOT TURNING & ONE BLADE APPEARED TO BE HANGING. THE PLT RPRTD THERE WAS NO WARNING OF AN IMPENDING ANTI-TORQUE CONTROL PROBLEM WHEN HE LOST CONTROL OF THE HELICOPTER. THE HELICOPTER THEN COLLIDED WITH TREES & CRASHED. INV REVEALED THE PLT HAD RPRTD AN OIL LEAK FM THE 90 DEG GEARBOX ON 4/11/89. THE COMPANY MECHANIC SUBSEQUENTLY REPLACED THE GEARBOX & A FUNCTIONAL TEST FLT WAS COMPLETED. THE ACDNT OCCURRED AFTER APRX ANOTHER 6 HRS OF OPN. AN EXAM OF THE TAIL ROTOR ASSEMBLY REVEALED THAT 1 OF THE 2 RETENTION BOLTS WERE MISSING FM THE TAIL ROTOR PITCH CHANGE CROSSHEAD. THREADED IMPRINTS WERE FND INSIDE THE RESPECTIVE CROSSHEAD RETENTION THRU-BOLT HOLE. THE RETENTION BOLT, NUT, WASHER & COTTER PIN WERE NOT RECOVERED. BOTH TAIL ROTOR BLADES CONTAINED CHORDWISE MARKS WHICH CORRESPONDED TO MARKS ON THE VERTICAL FIN (OPPOSITE OF THE TAIL ROTOR TIP PATH PLANE).
IMPROPER INSTALLATION OF A TAIL ROTOR PITCH CHANGE CROSSHEAD RETENTION BOLT BY THE COMPANY MECHANIC, WHICH RESULTED IN LOOSENING OF THE BOLT AND EVENTUAL FAILURE OF THE TAIL ROTOR ASSEMBLY/BLADE AND SUBSEQUENT LOSS OF CONTROL. TREES AT THE CRASH SITE CONTRIBUTED TO HELICOPTER DAMAGE.
Source: NTSB Aviation Accident Database
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