On September 25, 2000, approximately 1500 Pacific daylight time, a Robinson R-22 helicopter, N202RP, nosed over during a run-on landing at Corvallis Airport, Corvallis, Oregon. The certified flight instructor (CFI) and his student, who held a commercial pilot certificate, were not injured, but the aircraft, which was owned and operated by Pacific Rim Aviation, sustained substantial damage. The 14 CFR Part 91 local instructional flight, which had been airborne for about 45 minutes, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the CFI, the student was practicing a 180 degree autorotation to a planned power recovery over a taxiway adjacent to the runway. During the last part of the descent, the rotor rpm became low and the rotor low-rpm horn sounded. Although the CFI mentioned this to the student, the CFI was not concerned about the situation because he expected the rpm to increase when the student flared and began the power recovery. At the point where the student should have initiated his flare, he leveled the helicopter, but did not apply control inputs to stop its forward motion. As he attempted a power recovery, the helicopter continued to sink toward the ground and inadvertently made contact with the taxiway surface. At that point, the instructor took over, applied power, and tried to keep the aircraft from impacting the terrain a second time. Because the rotor rpm was still low, the aircraft settled to the taxiway surface a second time. At that point, the CFI transitioned to a run-on landing along the west edge of the taxiway. Although the helicopter was sliding along about 40 to 50 knots, it appeared to the instructor that it would slide to a stop on the taxiway. However, one skid slid off the left side of the asphalt surface, where it encountered soft terrain. The skid then sank into the terrain and the helicopter nosed over, coming to rest on its left side.