NTSB Identification: LAX94LA306.
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Accident occurred Friday, August 05, 1994 in PUUNENE, MAUI, HI
Probable Cause Approval Date: 05/09/1995
Aircraft: HUGHES 269C, registration: N8376F
Injuries: 2 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.

THE STUDENT WAS PERFORMING A PRACTICE AUTOROTATION AND AT 10 FEET HE BEGAN TO INCREASE THE COLLECTIVE TO CUSHION THE TOUCHDOWN. THE CFI SAID THE MAIN ROTOR RPM WAS LOW AND HE ADDED THROTTLE TO TOUCHDOWN WITH POWER. A GROUND RESONANCE VIBRATION BEGAN AND HE LIFTED OFF THE GROUND. THE VIBRATION CONTINUED AND HE ROLLED THE THROTTLE OFF AND SET THE HELICOPTER ON THE GROUND, THEN IT ROLLED OVER ON ITS SIDE. THE LANDING GEAR DAMPERS AND MAIN ROTOR DAMPERS WERE REMOVED AND TESTED AT THE FACTORY. THE RIGHT REAR AND LEFT FRONT MAIN LANDING GEAR DAMPERS HAD CHARGE PRESSURES BELOW ACCEPTABLE FACTORY SPECS. THE RIGHT FRONT AND LEFT REAR DAMPERS WERE FOUND TO BE WITHIN FACTORY SPEC RANGES. ALL THREE MAIN ROTOR DAMPERS WERE FOUND TO BE ADJUSTED TO EXCESSIVE FRICTION TORQUE VALUES. THE RED BLADE DAMPER WAS ASSEMBLED INCORRECTLY WITH A PLATE STACK UP IMPROPER FOR ANY VERSION OF THE DAMPER ASSEMBLY. THE HELICOPTER WAS IN STORAGE FOR 2 YEARS PRIOR TO JUNE 1994, WHEN IT WAS LEASED TO THE OPERATOR. THE RED BLADE DAMPER HAD BEEN REMOVED FROM ANOTHER HELICOPTER, OVERHAULED, AND PLACED IN SPARE PARTS INVENTORY, THEN PUT ON THE RED BLADE ON JULY 20, 1994.

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

the improper overhaul of the red blade main rotor damper, and the inadequate maintenance condition of the other rotor dampers and the landing gear dampers, which led to an uncorrectable ground resonance vibration and a subsequent rollover.

Full narrative available

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