What happened
While performing a hover taxi from the west side of the airport toward a hangar on the east side, the pilot of the unspecified helicopter lifted the aircraft to an altitude of approximately three feet. During this maneuver, the pilot noted that the cyclic began to rotate in a six to eight inch circle and reported hearing a low-pitch frequency oscillation.
The aircraft then entered a strong, uncontrollable roll to the left. Despite the pilot's attempts to push the cyclic to the right, the direction of movement could not be corrected. Recognizing that airplanes and personnel were in the flight path, the pilot elected to intentionally land the helicopter on its side to halt further movement. A witness observed the aircraft lift from the ramp to a height of 3 to 5 feet before the tail rotor struck the ramp, causing the aircraft to impact on its left side. The pilot was not injured.
The investigation
An examination of the aircraft revealed substantial damage to the cockpit area, skids, tail rotor, and main rotor blades. A review of the helicopter's systems showed no anomalies. During the previous annual inspection, a mechanic noted that the aircraft would experience a small amount of stick swirl during hover, though this issue could be mitigated by active control inputs.