What happened
A commercial certificated pilot was attempting to land a wheel/ski equipped helicopter on a metal landing grid. Upon the landing gear making contact with the grid, the aircraft began to experience vibrations caused by ground resonance. In an attempt to mitigate the vibration, the pilot immediately transitioned into a low hover.
However, the vibrations intensified as the pilot attempted to maneuver the aircraft away from the landing grid. The severity of the main rotor system's vibrations rendered the pilot unable to maintain control of the helicopter. During this period of instability, the main rotor blades struck a tower located approximately 30 feet from the landing grid. This impact caused the helicopter to strike the ground and roll into an inverted position.
The investigation
The investigation focused on the structural damage sustained during the event. The helicopter suffered significant structural damage to the fuselage, the tail boom, and all rotor blades. The pilot reported that there were no mechanical problems with the aircraft prior to the impact.
Findings
- The aircraft experienced ground resonance immediately upon touchdown on the metal grid.
- Severe vibrations in the main rotor system resulted in a loss of control.
- There were no injuries reported following the accident.