On November 21, 2006, about 1230 Pacific standard time, a Robinson R22 Beta, N994HV, encountered a dynamic rollover near Santa Clarita, California. Twin Air, Inc., was operating the helicopter under the provisions of 14 CFR Part 91. The certificated flight instructor and student were not injured; the helicopter sustained substantial damage. The local instructional flight departed Van Nuys Airport, Van Nuys, California, about 1145. Visual meteorological conditions prevailed, and a flight plan had not been filed. In a written statement, the flight instructor reported that the purpose of the flight was for the student pilot to review the maneuvers for the private pilot practical test standards. While en route to a practice area, the instructor determined the direction of the wind by comparing the indicated airspeed to the global positioning satellite displayed speed, and by observing dust behind a tractor operating in a field below. Both indicators verified that the wind was from the east. After the student demonstrated several maneuvers, the instructor decided to have him practice autorotations. He again confirmed that the wind was from the east. The instructor further stated that with the helicopter headed in an easterly direction, the student configured it for an autorotation. It descended, and they began the flare portion of the maneuver about 40 feet above ground level (agl). Despite their control inputs (adding throttle and raising the collective), it continued the descent, and settled toward the ground. The instructor took the controls, and initiated a power recovery. The aft section of the skids first touched the soft sandy surface, and it continued forward with very little airspeed. It pivoted about the right skid, and came to rest on its right side. The instructor reported that after egressing the helicopter, he noted a westerly wind. He opined that the wind had changed directions in the midst of their practice autorotation. He noted no mechanical malfunctions or failures with the helicopter prior to impact. A weather reporting station in Saugus, California, (about 3 miles northeast of the accident site) reported that between 1204 and 1244 winds were consistently from the south at 4 miles per hour (mph). In a written statement, another helicopter pilot who was practicing in the vicinity reported that he noticed a wind shift around the time of the accident.