On June 22, 1999, about 1430 Pacific daylight time, a Hughes 369D, N1089Y, registered to and operated by Olympic Air, Incorporated, was substantially damaged during landing following a practice autorotation. The accident occurred at Shelton Airport, Shelton, Washington. The commercial pilot, the sole occupant of the aircraft, was not injured. A company VFR flight plan was filed and visual meteorological conditions prevailed for this 14CFR91 flight. The flight originated from Rockaway, Oregon, approximately one hour prior to the accident. The pilot stated he was practicing autorotations from an altitude of approximately 200 feet above ground level (AGL) and an airspeed of approximately 50 knots. During the second practice autorotation, the pilot reduced power with throttle and used collective to adjust rotor speed to 410 RPM (minimum RPM for practice autorotations). The pilot stated the rotor RPM "quickly" decayed and the aircraft rapidly started to descend. Before the pilot was able to recover, the aircraft collided with the ground and rolled over. The aircraft sustained substantial damage to the main rotor blades, tail rotor, tail boom and fuselage. The pilot reported no mechanical failures or malfunctions with the aircraft at the time of the accident.