On July 27, 2000, at 0900 hours mountain standard time, a Robinson R-22 Beta, N888KB, experienced a tail rotor failure while standing with the engine and rotors idling in a field near Phoenix, Arizona. The aircraft sustained substantial damage; however, the student pilot, the sole occupant, was not injured. The aircraft was being operated as an instructional flight by Universal Helicopters, Inc., under 14 CFR Part 91 when the accident occurred. The flight originated in Wickenburg, Arizona, earlier that morning. Visual meteorological conditions prevailed at the time and no flight plan was filed. The pilot reported that he intended to land in a field used by the operator as a practice area in order to make some entries in his navigational log. He initiated his approach to the center of a field, terminating at a 5-foot hover. He then hovered forward about 150 feet looking for a smooth, level surface on which to touch down. After selecting his touchdown point, he performed a 360-degree pedal turn to determine wind direction and make certain he would be landing into the wind. He performed a smooth touchdown, reduced the throttle to idle, turned the governor off, and set the control frictions. He was at idle for about a minute, entering his flight time on his cross-country log and determining the heading for the final leg back to Scottsdale airport. In preparation for departure, the pilot released the control frictions and began to increase the throttle. As the power approached 95 percent, but before engaging the governor, the aircraft began to shake uncontrollably and the antitorque pedals began to move under his feet. He immediately reduced the throttle to idle, took out the checklist, and shutdown the aircraft per the instructions. After shutdown, the pilot exited the aircraft and inspected it for damage. He noted visible damage to the tail rotor and vertical stabilizer. He then notified the operator by cell phone and stayed with the aircraft until help arrived.