What happened
Following a recent overhaul of the main rotor blade dampers, a helicopter experienced severe mechanical instability during flight. Immediately after liftoff, the pilot reported intense vertical and lateral vibrations throughout the aircraft. During the vibration event, the pilot observed that one rotor blade was tracking 12 to 18 inches out of its normal plane.
As the pilot attempted to land the aircraft, the helicopter began to undergo structural failure due to ground resonance. The aircraft ultimately became non-operational as it came apart during the landing process.
The investigation
An inspection conducted by an FAA inspector focused on the main rotor blade dampers that had been overhauled just prior to the flight. The examination revealed that the dampers had not been reassembled in accordance with the manufacturer's maintenance manual. According to the manual, improper assembly of these components can directly lead to ground resonance and the subsequent destruction of the helicopter.