On August 19, 1997, at 1645 mountain daylight time, a Bell 47G-3B-2 helicopter, N2243W, made a hard landing during an autorotation training flight 5 miles north of Montrose, Colorado. The certified flight instructor pilot and commercially certificated student were not injured and the helicopter sustained substantial damage. The flight was being conducted under Title 14 CFR Part 91 as an instructional flight and no flight plan was filed. According to the flight instructor, the student was practicing power recovery autorotations and had completed nine. On the 10th autorotation, at approximately 20 feet, the student brought in power and leveled the aircraft and the instructor said he felt the throttle being applied. The low rotor horn sounded and the aircraft touched down hard causing the main rotor to flex and severe the tail boom. Examination of the engine and drive train, by an FAA inspector, following the accident provided no evidence of preimpact failure or malfunction. Density altitude at the time was 11,300 feet above mean sea level and according to the flight instructor, they were operating into the wind, which was westerly at 10 to 15 knots.