PUUNENE, MAUI, HI, USA
N8376F
HUGHES 269C
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.
On August 5, 1994, at 1215 hours Hawaii standard time, a Hughes 269C helicopter, N8376F, rolled over during the termination of a practice autorotation near Puunene, Maui, Hawaii. The helicopter was operated by the flight instructor and was on a local area dual instructional flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter sustained substantial damage. The certificated commercial pilot flight instructor and the dual student were not injured. The flight originated at Kahului, Maui, Hawaii, on the day of the accident at 1130 hours. In his statement, the flight instructor reported that the student was performing a practice autorotation from 800 feet agl. At 50 feet, the student began to apply aft cyclic control to slow the helicopter, and at 10 feet he began to increase the collective to cushion the touchdown. The instructor said the main rotor rpm was low and he added throttle to touch down with power. The instructor reported that immediately a ground resonance vibration began and he lifted off the ground. The vibration did not abate and the instructor rolled the throttle off and set the helicopter on the ground. During the touchdown, the helicopter rolled over on its side. The landing gear dampers and main rotor dampers were removed from the helicopter and sent to the Schweizer factory in Elmira, New York, for examination under the supervision of a Federal Aviation Administration (FAA) inspector from the associated Flight Standards District Office (FSDO). A copy of the test report is attached as an exhibit to this report. Compression tests of the right rear and left front main landing gear dampers revealed charge pressures below acceptable factory specifications. The right front and left rear dampers were found to be within factory specification ranges. All three main rotor dampers were found to be adjusted to excessive friction torque values. The red blade damper was found to be assembled incorrectly with a plate stack up improper for any version of the damper assembly. The helicopter maintenance records were examined by an FAA inspector from the Honolulu FSDO. He reported that the helicopter had been in storage for 2 years prior to June 1994, when it was leased to the current operator. The red blade damper had been removed from another helicopter, overhauled, and placed in spare parts inventory at Rotor Wing Hawaii, Inc., of Honolulu, Hawaii. The damper was put on the accident helicopter's red blade on July 20, 1994. Pertinent portions of the helicopter maintenance records and serviceable parts tag for the dampers are attached to this report.
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.
Source: NTSB Aviation Accident Database
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