On April 11, 1995, at 1048 Pacific daylight time, a Robinson R- 22B helicopter, N4015Y, rolled over during the touchdown phase of an autorotation at the Lampson Airport, Lakeport, California. The autorotation was precipitated by the activation of a low rotor rpm warning horn, which the pilot was unable to resolve. The helicopter was operated by Resort Aviation of Lakeport, and was on a student solo instructional flight. Visual meteorological conditions prevailed and included calm wind conditions. No flight plan was filed for the operation. The helicopter sustained substantial damage; however, the student pilot, the sole occupant, was not injured. The flight originated at the Lampson airport on the day of the accident at 1015 as a local traffic pattern practice student solo operation. A Federal Aviation Administration (FAA) airworthiness inspector from the Sacramento, California, Flight Standards District Office responded to the accident site, examined the wreckage, and interviewed both the student pilot and other company employees. In a verbal statement to the inspector, the student said he was performing takeoffs and landings in the traffic pattern for runway 28, and was on downwind when the low rotor rpm warning horn activated. The student said he was unsuccessful in extinguishing the warning horn by throttle and collective manipulation and entered an autorotation. The student reported that he did not verify the main rotor rpm by reference to the rotor tachometer. During the touchdown, about 1/4-mile southeast of the airport in a soft field, the skids dug into soft soil and the helicopter rolled over. The inspector examined the aircraft and engine, which included an engine start and static run-up. The engine started normally and was successfully exercised throughout its normal power range. The inspector examined the maintenance records for the helicopter and interviewed both company flight instructors and maintenance personnel. The maintenance records revealed a history of false low rotor rpm warning horn activations in the accident helicopter dating back to July of 1994. After pilots would report the warning horn discrepancy to maintenance personnel, some system component would be changed and the helicopter returned to service; however, the problem persisted. In written statements, company flight instructors reported that the accident helicopter was the only one the company had, and they felt compelled by management to fly the aircraft with the unresolved discrepancy. The instructors stated that they trained the students, including the accident pilot, how to cope with the nuisance warning.