Incident Overview
A commercial certificated pilot reported that he was attempting to land a wheel/ski equipped helicopter on a metal landing grid. As soon as the landing gear touched the grid, the helicopter began to vibrate in ground resonance. The pilot immediately lifted the helicopter into a low hover, but the vibrations increased. He attempted to move the helicopter away from the landing grid but indicated that he was unable to control the helicopter due to the severe vibrations of the main rotor system.
Sequence of Events
During the attempted departure from the grid, the helicopter's main rotor blades subsequently struck a tower located about 30 feet from the grid. This impact caused the helicopter to strike the ground and roll inverted. The pilot stated that there were no preimpact mechanical problems with the helicopter.
Damage Assessment
The helicopter sustained structural damage to the fuselage, tail boom, and all rotor blades. The accident sequence resulted in the helicopter coming to rest inverted on the ground.
Pilot Report
The pilot, who held a commercial certificate, reported the sequence of events and noted that the vibrations were severe enough to prevent control of the helicopter. He confirmed that no mechanical issues existed prior to the accident.