On May 7, 1995, about 1130 eastern daylight time, a Robinson R22 Beta helicopter, registered to Metro Helicopter, Inc., operated by Ace Helicopter Corp., landed hard at the Kendall- Tamiami Executive Airport, Miami, Florida, while on a 14 CFR Part 91 instructional flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was substantially damaged and the certified flight instructor (CFI) and student were not injured. The flight originated about 1040 from the Kendall-Tamiami Executive Airport, Miami, Florida. The CFI stated that the student pilot was performing a practice autorotation with power recovery. The entry altitude and airspeed were 600 feet and 75 knots. The glide airspeed stabilized at 65 knots and at 100 feet, the rotor rpm was in the green range, the airspeed was 60 knots, and the rate of descent was 1,500 feet per minute (fpm). At 100 feet the student initiated the flare and at 40 feet, forward cyclic and power were applied. The main rotor rpm then began to decay and the helicopter impacted the ground hard. A section of the tailboom was then severed by the main rotor blades. The CFI stated that there was no engine or airframe preimpact failure or malfunction. According to the airframe manufacturer pilot's operating handbook normal procedures section and the flight training guide, the stated altitude to initiate the flare is about 40 feet above ground level (agl). At about 8-10 feet agl, apply forward cyclic to level the helicopter and raise collective to stop the descent. Additionally, power as required to keep the rpm in the green arc.