On July 15, 2005, about 0900 mountain standard time, a Robinson R-22 Beta II, N7514P, impacted the terrain and rolled over during a practice hovering autorotation at the Williams Gateway Airport (KIWA), Mesa, Arizona. Sliver State Helicopters was operating the helicopter under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) and pilot undergoing instruction (PUI) were not injured; the helicopter sustained substantial damage. The local instructional flight departed Mesa, Arizona, about 0835. Visual meteorological conditions prevailed, and no flight plan had been filed. In a written statement, the CFI stated that the purpose of this instructional flight was to prepare the PUI for the Robinson Safety Course. They had planned on practicing several maneuvers, which included hovering autorotations. The CFI reported that they positioned the helicopter in a hover over taxiway hotel between taxiway Charlie and runway 30R to practice hovering autorotations. On the third attempt at the hovering autorotation, they stabilized the helicopter in a 2-foot hover. The PUI counted down "three, two, and one" and entered the maneuver. He then increased the throttle, as opposed to retarding the throttle, and simultaneously added full right antitorque pedal. The helicopter then began to rapidly yaw to the right. The CFI then retarded the throttle and tried to overcome the PUI's right antitorque pedal input. At this point, the helicopter was starting to descend, and the right yawing motion was beginning to slow down. As the helicopter descended towards terrain, the low rotor rpm horn and light went off, and the CFI lowered the collective in an attempt to stop the descent. Shortly thereafter, the helicopter impacted the terrain, and rolled over on its right side facing 180 degrees from the initial starting point. The resulting damage was to the main rotor blades, tail rotor blades, and tail boom. The pilot stated that the helicopter and engine had no mechanical failures or malfunctions during the flight. According to the Rotorcraft Flying Handbook (FAA-H-8083-21), when performing hovering autorotations the pilot is to firmly roll the throttle into the spring loaded override position, if applicable. This disengages the driving force of the engine from the rotor, thus eliminating torque effect. As the throttle is closed, apply proper antitorque pedal to maintain heading.