On August 7, 1996, at 0900 hours Pacific daylight time, a Bell UH-1H, N499DF, collided with the runway while performing a practice autorotation at Ukiah Municipal Airport, Ukiah, California. The aircraft sustained substantial damage; however, neither the flight instructor nor his commercial student was injured. The aircraft was being operated as an instructional flight by the California Department of Forestry. The flight originated in Willits, California, at 0745. Visual meteorological conditions prevailed and a company VFR flight plan had been filed. According to the statements of both pilots, after first practicing a few confined area and slope landings, they flew to the Ukiah Airport. At Ukiah the instructor conducted emergency procedure training, which consisted mainly of autorotations terminating with power recoveries. He felt that the pilot had been having difficulty maintaining situational awareness during the previous confined area operations. The training continued with a series of straight in autorotations, with the touchdown point planned to be about midfield on runway 15. During the first three or four autorotations, the instructor pilot had to take control of the collective because she allowed the N2 to overspeed. She was also having problems with aircraft control, primarily during flare, initial pitch application, and recovery. The instructor estimated they had performed 10 to 15 straight in autorotations prior to the accident. During the final autorotation, the instructor described her flare as "very gradual." She had allowed the aircraft to descend to approximately 10 feet agl, with the aircraft was still in a near level attitude, when she began a power recovery. As she was rolling on the throttle, she inadvertently made an abrupt aft cyclic control movement. The stinger and tail rotor struck the ground before the instructor could regain control. After the tail rotor strike, the instructor stabilized the aircraft at a 3- to 4-foot hover. When he checked the controls he noticed a vibration and realized the aircraft had been damaged. He had hovered off the east side of runway 15 and was setting the aircraft down when the vibration became worse. During the aircraft shutdown, the tail rotor and tail rotor gearbox separated from the tailboom. The crew exited the aircraft without further incident. Fresh scrapes and gouges were observed on the runway surface. The left- and right-hand synchronized elevator, as well as the tail boom vertical fin and spar, had structural damage. The second stage power turbine wheel exhibited foreign object damage (FOD) on two blades. A tail rotor control tube and a synchronized elevator control tube also exhibited damage. The pilot had previously received 5.4 hours of initial training from the instructor between June 25 and June 27, 1996. On June 28, 1996, the pilot received a check ride from the CDF air operations officer. A pilot qualification card was issued with the provision that she receive additional training and a reevaluation check ride. The pilot then went on 2 weeks active duty for training (ADT) with the California Army National Guard at Los Alamitos AAF where she received additional training in the UH-1H helicopter. A telephone conversation between the CDF safety officer and her National Guard instructor pilot indicated that the pilot continued to have difficulties with aircraft control.