On June 28, 2003, at 1715 mountain daylight time, a Schweizer 269C helicopter, N3623U, was substantially damaged when it impacted terrain during aerial taxi at Bountiful-Skypark Airport (BTF), Bountiful, Utah. The commercial pilot was uninjured. The local flight was being conducted under Title 14 CFR Part 91 without a flight plan. Visual meteorological conditions prevailed at the time of the accident. The flight had originated at approximately 1615, and was taxiing to parking when the accident occurred. The pilot reported that during the hour previous to the accident he had been flying in the pattern at BTF. The pilot said that he was hover taxiing from the west side of the airport to his hangar on the east side. He said he had lifted the helicopter "up to about a three-foot hover," when the cyclic started to rotate "in about a six to eight inch circle" in his hand. The pilot reported he heard a "low pitch or frequency oscillation." The pilot said, "The helicopter started a strong uncontrollable roll to the left. I tried to push the cyclic to the right but found no change in stopping the roll or direction of movement." The pilot said that he knew there were airplanes and people in the direction the helicopter was heading. The pilot said he decided to put the helicopter down on its' side to stop any further movement. A witness said the helicopter lifted off the ramp approximately 3 to 5 feet. The tail rotor then struck the ramp and the helicopter impacted on its left side. An examination of the helicopter at the accident site showed substantial damage to the main rotor blades, rotor head, tail rotor, and both skids. The Plexiglas windscreen was broken out and fragmented. Flying fragments from the helicopter struck and caused damage to two airplanes, a hangar wall, and a mechanics shop door. The helicopter was further examined the week of August 26, 2003. Flight control continuity was confirmed. Flight control action was smooth. An examination of the main rotor, engine, engine controls, and other helicopter systems revealed no anomalies that could have contributed to the accident. At 1656, the wind conditions at Salt Lake City International Airport, 5 nautical miles south of BTF were 350 degrees at 11 knots with gusts to 16 knots. According to the mechanic who had performed the previous annual inspection on the helicopter; when in a hover, the helicopter would experience a small amount of stick swirl. The mechanic said that "if you work it, it [the swirl] will go away."