Accident Description
Witnesses reported hearing a loud noise while the helicopter was flying at an altitude between 100 and 150 feet above ground level. They observed an object falling from the tail boom. The helicopter immediately pitched nose-down and began a right spin. It then impacted on a rocky island and came to rest in the adjacent water.
Findings
Post-accident examination revealed that the tail rotor gearbox, tail rotor hub, and one tail rotor blade were not located. A second tail rotor blade was found along the flight path, broken into two pieces approximately 150 feet from the main wreckage. The tail rotor gearbox had separated due to overstress, and all fractures of the recovered tail rotor blade were characteristic of overstress. The recovered blade showed no impact marks on its leading edge or tip.
No pre-crash failure or malfunction was found in the remaining structure, flight controls, main rotor blades, transmission, or engine.
Maintenance History
The helicopter had experienced a tail rotor strike 130 flight hours before the accident. Following that event, the tail rotor blades were replaced, but the hub was not changed as required by the manufacturer's instructions. The helicopter was being operated for hire and had flown 130 hours since its last maintenance inspection.
Center of Gravity Considerations
Calculations indicated that during takeoff, the helicopter's center of gravity was 3.4 feet forward of the forward limit. With the loss of the separated tail rotor components, the center of gravity would have moved approximately 2 feet further forward.