Accident Details
Shortly after liftoff, the pilot experienced severe vertical and lateral vibrations. Observing that one rotor blade was tracking 12 to 18 inches out of the normal plane, the pilot initiated a landing. As the helicopter touched down, ground resonance developed, causing the aircraft to break apart.
Maintenance Findings
An FAA inspector examined the main rotor blade dampeners, which had been overhauled just before the flight. The inspection revealed that the dampeners had not been reassembled in accordance with the manufacturer's maintenance manual.
Manufacturer's Guidance
The maintenance manual explicitly stated that improper assembly of the blade dampeners could lead to ground resonance and destruction of the helicopter. The observed failure sequence matched this warning.