On December 14, 2000, at 1402 hours Pacific standard time, a Robinson R22 Beta, N7189K, was substantially damaged during a practice 180-degree autorotation landing to a flood control basin, 8 miles northwest of the North Las Vegas, Nevada airport. During the landing the helicopter touched down hard, the main rotor severed the tail boom, and the helicopter rolled over. The commercial certificated flight instructor/first pilot received minor injuries and the commercial certificated flight instructor/second pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the instructional flight that originated at North Las Vegas about 1330. The flight was operated under 14 CFR Part 91 by West Air Helicopters. The first pilot was a senior instructor, and the purpose of the flight was to evaluate the second pilot for hire as a flight instructor. They proceeded to a floodwater retention basin that the operator used as a practice area. The elevation was 3,400 feet mean sea level. The first pilot reported there were no mechanical problems with the helicopter. In his report to the Safety Board, the first pilot reported that he asked the second pilot to demonstrate some straight in and 180-degree autorotation landings. During four of six autorotations it was necessary for the first pilot to assume control of the helicopter and make power recoveries due to high landing flares, improper airspeed, and improper rotor rpm. During the seventh autorotation, the landing approach that resulted in the accident, the first pilot stated that the second pilot first let the main rotor rpm get too high, then too low, and then let airspeed get low. The first pilot took control and applied engine power, but this time, as the ground approached more rapidly than before due to recovery from a low airspeed and low rpm condition, the second pilot "began to scream" and interfered with the first pilot's control by pulling up on the collective. The first pilot could not overpower him, the rotor rpm decayed, and a hard landing resulted. In his report to the Safety Board, the second pilot reported that, as he initiated the final autorotation, the first pilot said "hold on, hold on," and the second pilot thought he was again taking the controls and relinquished them to him. As the helicopter continued the descent, the first pilot continued to say "hold on, hold on," and the second pilot became worried because the ground approached rapidly and the low rpm horn had been on for several seconds. When the second pilot realized they were going to crash and the first pilot wasn't doing anything to arrest the situation, he (the second pilot) took the controls and tried to flare and pulled full up collective to cushion the landing.