On March 21, 2001, at 1145 hours Pacific standard time, a Robinson R22B, N8492A, made a hard landing and severed the tail boom at the Long Beach/Daugherty Field Airport, Long Beach, California. The helicopter was operated by Rainbow Air Academy, Inc., under the provisions of 14 CFR Part 91 as a local area instructional flight, and sustained substantial damage. The certified flight instructor (CFI) and private helicopter pilot were not injured. Visual meteorological conditions prevailed for the flight. The flight departed the airport at 1115, and was scheduled to terminate there. No flight plan had been filed. In the CFI's written statement to the Safety Board, he stated that the purpose of the flight was to prepare the private pilot for his commercial pilot practical flight test. The private pilot had control of the helicopter with the CFI monitoring the flight. They made two takeoffs and landings, with no discrepancies noted. The CFI then instructed the student to do an autorotation. He said the first approach "was not bad." He did note that the airspeed was below 60 knots and the rotor rpm was "getting higher into the top of the green arc." The CFI instructed the pilot to keep his airspeed at 65 knots until they were close to the ground, and to keep the rotor rpm inside the "green arc." He also instructed the pilot to raise the collective to maintain rotor rpm. On the second approach, the airspeed was below 60 knots, but he kept the rotor rpm inside the green arc. As they got closer to the ground, the airspeed dropped to 58 knots and the rotor rpm was moving towards the bottom of the green arc. The low rotor rpm warning horn sounded and the caution light illuminated. The CFI stated that the normal procedure for a low rotor rpm recovery is to lower the collective or move the cyclic to the aft position. The CFI stated that he came up on the flight controls and noted that the collective was higher than normal. He stated that he could not lower the collective because of the proximity of the helicopter to the ground. He instead started the flare for landing. The rotor rpm continued to get lower. Forward pressure was applied to the cyclic to keep a level attitude after touchdown. The helicopter slid across the ground without bouncing. After they came to a stop the CFI noted there was no response from the anti-torque pedals. He saw that the tail rotor cone was broken and bent down at the anti-collision light. The private pilot stated that he had conducted two normal takeoffs and landings, two approaches, and two hovering autorotations, as well as two straight-in autorotations. On the accident autorotation he adjusted the collective to maintain rotor rpm in the green arc, but noted that the airspeed fell to 58 knots. Prior to the flare he heard the low rotor rpm horn sound. He stated that he believed that the rotor rpm would recover during the flare. After entering the flare he stated that the rotor rpm did not increase. The pilot stated that due to the closeness of the ground he was unable to perform a successful low rotor rpm recovery. He confirmed that the helicopter slid across a grassy area and the tail cone and anti-collision light was broken.