On February 28, 2000, at about 1030 eastern standard time, a Hughes TH-55, N9518K, registered to Pasco County Mosquito Control, operating as a 14 CFR Part 91 training flight crashed during a training autorotation. Visual meteorological conditions prevailed and no flight plan was filed. The helicopter sustained substantial damage. The commercial pilot reported no injuries. The pilot departed from a private state heliport about 30 minutes before the accident. The pilot stated he was conducting an autorotation with turn. He started his deceleration between 75 to 100 feet. The helicopter was not slowing down, he applied aft cyclic and the helicopter entered into a vertical rate of descent. Collective pitch was increased, the helicopter collided with the ground in a tail low attitude separating the tail boom, and rolled over on its right side.