HISTORY OF FLIGHT On April 2, 1995, at 1140 hours Pacific daylight time, a Robinson R22 Beta, N2323K, sustained substantial damage during a practice autorotative landing near Healdsburg, California. The helicopter was owned and operated by Peregrine Helicopters, Inc., and was on a dual instructional flight. Visual meteorological conditions were prevalent at the time and no flight plan had been filed for the operation. Neither the certified flight instructor nor her certificated private pilot student were injured. The flight originated from the Sonoma County Airport, Santa Rosa, California, at 1040 on the day of the accident. The instructor reported that the student had been performing autorotative landings with power recoveries to a river sandbar. After completing two 180-degree autorotations, the student initiated a straight-in autorotation from 550 feet agl. The instructor reported that during the descent airspeed and rpm were maintained within limits. The instructor reported that the student initiated his flare at 40 feet agl, but that he applied aft cyclic so abruptly and with such force that she was unable to counteract the movement. The helicopter continued to descend in a tail-low attitude until the stinger and tail rotor struck the ground, buckling the tailboom. After the tail struck the ground, the student relinquished the controls and the instructor landed the aircraft. The instructor reported that winds at the accident site were light and variable.