What happened
The pilot attempted to operate the helicopter at its maximum gross weight. After lifting the aircraft into a hover and stabilizing the rotor RPM, the RPM began to decrease. Unable to recover the RPM, the helicopter settled back to the ground and entered a ground resonance condition. The pilot responded by closing the throttle and lowering the collective; during this process, the aircraft shuddered and rotated 45 degrees to the left before the resonance subsided.
The pilot then successfully re-established a stable hover with stabilized engine and rotor RPM, even performing a left pedal turn. However, while attempting to transition into forward flight, the rotor RPM dipped a second time. This forced the pilot to set the aircraft down again. Upon landing, the helicopter entered ground resonance for a second time. This second event was more severe than the first, causing the aircraft to be shaken apart around the pilot and the passenger. The incident resulted in 2 injuries.
The investigation
Post-accident testing focused on the landing gear components. The investigation revealed that all four landing gear dampers had failed a load stroke test. Specifically, the dampers were set too hard, which contributed to the onset of the ground resonance condition following the reduction in rotor RPM.