On July 19, 2001, about 1540 eastern daylight time, a McDonnell Douglas 369E, N577DB, was substantially damaged when it rolled over during landing, at the operator's facility in Niagara Falls, New York. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the positioning flight that departed a helipad in Niagara Falls, New York, about 1530. No flight plan was filed, and the flight was conducted under 14 CFR Part 91. According to the pilot he was re positioning the helicopter so it could be placed in a hangar. He departed a helipad and flew about 4 minutes to the operator's facility. He then came to a hover over a helicopter-dolly with the wind to the front left of the helicopter. The pilot lowered the collective, and the helicopter touched down softly. The skids on the helicopter were lined up with the white touchdown markings, but the pilot felt that the right skid was not situated properly on the dolly. As the pilot increased collective to reposition the helicopter, it rolled to the right, and impacted the ground. The pilot then executed an emergency shut down, and exited the helicopter. According to a Federal Aviation Administration inspector, the landing surface on the helicopter-dolly was constructed of wooden boards that measured 8 inches wide by 2 inches thick. To hold the landing surface boards in place, there were two additional wooden boards, each measuring 4 inches wide by 2 inches thick, attached perpendicular to the underside of the landing surface with metal screws. Examination of the helicopter-dolly revealed that both sets of boards were intact, and that the metal screws had sheared consistent with overload. About 15 minutes after the accident, Niagara Falls International Airport (IAG), Niagara Falls, New York, which was located approximately 3 miles to the southeast of the accident site, recorded the following weather: wind 070 at 8 knots, visibility 12 miles, few clouds at 4,500 feet, ceiling 6,500 feet broken, 18,000 feet overcast, temperature 82 degrees Fahrenheit, dew point 68 degrees Fahrenheit, and an altimeter setting of 30.11 Hg. According to Advisory Circular 90-87, Helicopter Dynamic Rollover, if a rolling moment is allowed to develop while one skid is in contact with the ground, the helicopter can exceed its critical rollover angle. As the helicopter begins to roll, lateral cyclic control response becomes more sluggish and less effective than for a free hovering helicopter. As the roll rate increases, the angle at which recovery is still possible is significantly reduced. The pilot reported 2,200 hours of total flight experience, all of which was in turbine helicopters. The pilot added that he had about 200 hours in the accident helicopter make and model, with 35 hours of that being in the actual accident helicopter.