On August 16, 2010, about 1445 eastern daylight time, a Bell UH1H helicopter, U.S. Customs tail number 21769, and no Federal Aviation Administration registration number, was substantially damaged during a practice autorotation at Warrenton-Fauquier Airport (HWY), Warrenton, Virginia. The helicopter was operated by U.S. Customs and Border Protection. The certificated commercial pilot and flight instructor were not injured. Visual meteorological conditions prevailed at the time, and a visual flight rules flight plan was filed for the public use training flight. The flight originated at Manassas, Virginia (HEF) at 1400. The pilot receiving instruction reported that he was attempting a practice autorotation to runway 33 from 1,800 feet. During the touchdown, the pitch of the helicopter increased and the tail rotor and stinger contacted the runway. The flight instructor immediately pitched the helicopter forward to arrest the tail-low condition when the helicopter began to shudder. Both pilots worked to maintain aircraft control and the helicopter pivoted to the right due to the loss of tail rotor control. The helicopter struck the runway in a left-skid-low condition and came to rest near the taxiway exiting runway 33. The pilots reported that there were no mechanical anomalies with the helicopter during the autorotation. The pilot receiving instruction reported about 3,500 hours of helicopter flight time, including 100 hours in the UH1H. He also reported 20 hours in the 90 days prior to the accident and 10 hours in the 30 days prior to the accident. A cursory examination of the wreckage revealed the tail rotor was separated and the vertical stabilizer was severed. The 1440 weather observation for HWY included the following: scattered clouds at 3,700 feet, ceiling broken at 4,400 feet, surface winds from 230 degrees at 6 knots, 10 statute miles visibility, temperature 35 degrees Celsius, dew point 22 degrees Celsius, and an altimeter setting of 29.94 inches of mercury.