On May 21, 1999, at 1605 central daylight time, a Robinson R22 Beta, N215WW, piloted by a private pilot, was substantially damaged when it collided with the terrain following a loss of control during a practice pinnacle approach, near East Troy, Wisconsin. Visual meteorological conditions prevailed at the time of the accident. The personal flight was conducted under the provisions of 14 CFR Part 91 and was not on a flight plan. The pilot reported no injuries. The local flight departed East Troy Municipal Airport, East Troy, Wisconsin, at 1530, and was practicing flight maneuvers at the time of the accident. According to the pilot's written statement, he was practicing a pinnacle approach to a specific point in a fallow farm field. The pilot reported that he conducted a high reconnaissance, at an altitude of approximately 500 feet above ground level (agl), then performed a traffic pattern around his predetermined landing point. The pilot stated that he then began a descent towards the landing point and at an altitude of approximately 10 feet agl he began his final vertical descent. The pilot reported that the aircraft began to, "...shudder violently," and he made the determination that the shuddering was a result from settling with power. The pilot stated that he tried to maneuver the helicopter out of the rotor-blade turbulence by moving the cyclic forward but the aircraft began to descend at an increasing rate. The pilot reported that he was too low to lower collective and he tried to arrest the descent by increasing the helicopter's pitch. The aircraft impacted the ground on the skids and rolled over on the windscreen. The retreating main rotor blade struck the tail-boom separating it from the helicopter.