On January 29, 2005, approximately 1135 mountain standard time, a Hughes 269C helicopter, N9688F, piloted by a commercial certificated flight instructor, was substantially damaged when it made a hard landing at Centennial Airport (APA), Englewood, Colorado. Visual meteorological conditions prevailed at the time of the accident. The local instructional flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The flight instructor and student pilot reported no injuries. The flight originated at Centennial Airport approximately 1040. The following is based on a telephone interview with, and written statement from, the flight instructor: The instructor and his student were practicing autorotations. The instructor demonstrated a "360 degree autorotation" to the student from an altitude of 600 feet agl with a power recovery. He then returned to an altitude of 600 feet agl, where he, "rolled off the throttle to initiate the maneuver [for the student]." The student lowered the collective and began a right turn. As he was completing the first 180 degrees of turn, the instructor noticed that the "rotor rpm was at the top of the green arc, so [he] applied collective to maintain rotor rpm." Approximately 270 degrees into the turn, rotor rpm had decayed and the instructor lowered the collective in an attempt to maintain rotor rpm. He then noticed that the airspeed had dropped to 40 knots and a high rate of descent had developed. The instructor applied power, then, rolled out of the turn and leveled the aircraft for a run-on landing. The instructor could not arrest the descent rate, and the helicopter touched down on the right skid. The skid collapsed and the helicopter skidded to a stop. All three main rotor blade tips were bent and the airframe was damaged on the right side as a result of the ground strike.