On January 11, 2002, at approximately 0840 mountain standard time, a McDonnell Douglas MD 902 helicopter, N902AM, operated by MD Helicopters, was substantially damaged during a hard landing in a field near Aurora, Colorado. The flight instructor, a pilot receiving instruction, and one passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for this local training flight being conducted under Title 14, CFR Part 91. The flight originated from Centennial Airport, Englewood, Colorado, at approximately 0750. According to the instructor, he was conducting transition training and was demonstrating emergency procedures on anti-torque malfunctions and loss of thrust/fixed pedal settings. After reaching final approach at approximately 80 knots forward airspeed, and at approximately 100 feet above ground level, he began to demonstrate how to complete an approach with a loss of directional control or "Anti-Torque Failure- Fixed Thruster Setting." He identified an intended termination area, and established the helicopter on a "shallow" approach angle with a deceleration attitude of approximately 15 to 20 degrees nose up and approximately 300 feet per minute rate of descent. The flight profile "appeared normal" until about 50 to 60 feet above ground level when the helicopter started to descend at a higher than desired rate for demonstration. The pilot applied collective lever control and a shudder was felt in the rotor system, followed by an increase in descent rate. Collective lever application could not arrest the descent. The helicopter struck the ground hard in a nose high attitude, ballooned into the air approximately 3 to 5 feet and slowly rotated approximately 360 degrees. The "thruster" was jammed in the neutral position and the "fan would stall making popping sounds," but he had no problem landing the helicopter from a hover with power. The helicopter sustained substantial damage to the Notar (No Tail Rotor) Anti-Torque rotating thruster cone, the aft cross tube, and both landing gear skids. The pilot stated that he encountered "vortex-ring-state" while trying to slow the helicopter, and that it "put me on the ground at a very high rate of descent." The initial higher rate of descent may have been due to the higher density altitude at the training site than is normally encountered at his home station in Mesa, Arizona. At 0853, the reported weather at Centennial Airport (APA), Englewood, Colorado (approximately 12 nautical miles west of the accident site, and at an elevation of 5,883 feel msl) was, wind, 220 degrees at 8 knots; visibility, 10 statute miles; sky condition, few at 12,000 feet; temperature, 7 degrees C. (44.6 degrees F.); dew point, minus 12 degrees C. (10.4 degrees F.); altimeter setting, 30.24. The calculated density altitude was 6,022 feet msl.