On April 11, 2003, at 1030 mountain daylight time, a McDonnell Douglas 369E, N91620, registered to and operated by the U.S. Border Patrol Air Operations as a public use operation, rolled over at the Sher-Wood Airport, Plentywood, Montana. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was substantially damaged and the commercial pilot and passenger/observer were not injured. The flight originated from Glasgow, Montana, about one hour and ten minutes prior to the accident. In a written statement, the pilot reported that the helicopter was hovering about three feet above the taxiway, when he began to make a 180 degree left pedal turn. As the tail of the helicopter passed through the downwind portion of the turn, the tail rose sharply. The pilot applied abrupt aft cyclic control. The tailrotor struck the pavement, followed by a loss of tail rotor authority and an uncommanded rapid spin to the right. Throttle was reduced as the pilot attempted to perform a hovering autorotation. The helicopter touched down in a level attitude, but with excessive lateral movement. The right side landing skid collapsed and the helicopter rolled to the right coming to rest on its right side. The pilot reported the weather at the time as clear, with greater than 10 miles visibility. The temperature was 65 degrees F, and the wind was reported from 175 degrees at 21 knots, gusting to 28 knots. The pilot reported no mechanical failures or malfunctions with the helicopter at the time.