Incident Summary
A helicopter experienced substantial damage during an aborted takeoff from a helicopter-landing pad. According to the pilot, the helicopter was started and a full run-up of both engines and all systems was performed. Both engine FADEC Power Management Switches were verified in the 'Flight' position, and the collective-mounted 100 percent/102 percent switch was set to '102'. The number 1 Electronic Display Unit showed three vertical yellow lines indicating both engines’ rpm at 102 percent and that the rotor rpm was co-joined with them.
Pilot Actions
The pilot lifted the helicopter into a five-foot hover. After approximately 30 seconds of normal hovering flight, a 'bang' was heard. The helicopter then began to settle vertically, and the pilot observed multiple caution and warning lights on the number 1 Electronic Display Unit. The aircraft oscillated laterally as it settled, with a rapid loss of rotor rpm. The pilot used the collective pitch lever to cushion the landing using the remaining rotor rpm. Upon the left main wheel touching down gently, the helicopter entered a violent lateral oscillation described as ground resonance. Despite the collective pitch lever being in the full down position, the oscillation increased in severity. The left main landing gear subsequently collapsed, and the helicopter settled onto its left sponson. The tail rotor blades made contact with the ground. The lateral oscillation continued, and the nose swung to the left following the main rotor rotation. The pilot then shut down both engines, and the main rotor blades coasted to a stop.
Examination Results
On-site examination indicated that the damage to the helicopter was consistent with ground resonance. Both engines were run on an engine test stand and showed no anomalies that would prevent normal operation. Examination of the non-volatile memory of the engine electronic controls for both engines revealed no preexisting anomalies or fault codes associated with the accident flight. Inspection of the flight controls and aircraft systems likewise found no anomalies associated with a preexisting condition.