Accident Details
The pilot initiated the flight with the helicopter at maximum gross weight. After lifting the helicopter to a hover and stabilizing the rotor RPM, the RPM began to decrease. Unable to recover the RPM, the helicopter settled to the ground, subsequently entering a ground resonance condition. The pilot closed the throttle and lowered the collective, and the helicopter began to shudder before turning 45 degrees to the left. The ground resonance condition then subsided.
The pilot then successfully lifted the helicopter again to a hover, stabilizing the engine RPM, and maintained a stable hover while sustaining rotor RPM during a left pedal turn. While attempting to transition to forward flight, the helicopter's RPM dipped again, forcing the pilot to set the helicopter down. Upon landing, the aircraft entered ground resonance a second time, which was more severe than the first. The helicopter shook apart around the pilot and the passenger.
Post-Accident Findings
Post-accident tests on all four landing gear dampers indicated that they had failed a load stroke test. The dampers were set too hard, resulting in a ground resonance condition being encountered after a landing due to reduced rotor RPM.