On May 30, 2010, about 1245 central daylight time, a Bell 206B, N6401X, operated by the City of Memphis Police Department, was substantially damaged during a practice autorotation at the Memphis Police Department Heliport (27TN), Memphis, Tennessee. The certificated flight instructor and certificated commercial pilot were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The public use training flight was operating under the provisions of 14 Code of Federal Regulations Part 91. According to the flight instructor, after takeoff, they remained in the traffic pattern to conduct flight maneuvers. After about 20 minutes, as the commercial pilot was climbing the helicopter through approximately 450 feet, the flight instructor rolled the throttle back to flight idle to simulate an engine failure. He then advised the commercial pilot to terminate the maneuver with a power recovery. The commercial pilot immediately lowered the collective and entered an autorotation. Approximately 100 feet above the ground, the flight instructor advised the commercial pilot to increase the throttle to full power. Shortly thereafter, the flight instructor heard the low rotor warning signal, and “got on the controls with the pilot.” The flight instructor advanced the throttle to 100 percent power, as both pilots remained on the controls. During the flare, the tail stinger struck the ground and the helicopter landed hard. The main rotor came into contact with the tail boom aft of the horizontal stabilizer and severed it. Examination of the helicopter by a Federal Aviation Administration inspector revealed that the helicopter came to rest on the helipad, and that the tail boom was severed aft of the horizontal stabilizer. Examination of the airframe and flight control system components revealed no evidence of preimpact mechanical malfunctions, and neither pilot reported any flight control or engine anomalies.