Primary finding
Probable cause
failure of the rotor drive system clutch assembly which rendered the aircraft uncontrollable.
Investigator assessment
Analysis narrative
Approximately 20 minutes after takeoff on a cross-country flight, the pilot noticed the clutch light was on and he smelled burning rubber. The pilot conducted a power on autorotation and at approximately 50 feet above the ground, he heard a loud "pop" and the aircraft "dropped" to the ground, skidded about 15 feet, and rolled over on its side when a skid collapsed. Inspection revealed that the upper clutch actuator bearing had failed. All required inspections regarding the bearing assembly had been performed. Procedures used by the manufacturer require both the pilot and mechanic to listen for unusual bearing noise at specific intervals.
Source record
Factual narrative
On March 11, 2001, at 1320 mountain standard time, a Robinson R22 Beta, N144MB, sustained substantial damage during a forced landing approximately 20 miles east of Buffalo, Wyoming. The private pilot, the sole occupant, was not injured. The flight was a cross-country flight from Gillette, Wyoming, to Bozeman, Montana, and was being flown under Title 14 CFR Part 91. No flight plan was filed, and visual meteorological conditions prevailed. The flight departed Gillette Wyoming, at 1300. According to the pilot, he was in cruise flight about 2,200 feet above the ground when the clutch light came on and he smelled burning rubber. The pilot reportedly did a power on autorotation and at approximately 50 feet above the ground, he heard a loud "pop" and the aircraft "dropped" to the ground and skidded about 15 feet. The right skid broke off and the aircraft rolled on its right side. The fuselage and rotor system suffered substantial damage. Examination of the helicopter provided evidence of a failure of the upper actuator bearing, part number A-184. The bearing assembly is pressed onto the clutch shaft and is used as a point of attachment for one end of the V-belt tightening actuator. The other end is attached to a pulley, which presses against the V-belts when the actuator is activated. The actuator is electrically actuated to extend, which tightens the V-belts and enables the engine to supply power to the drive train. The actuator/bearing assembly requires inspection during the 100 hour inspection. An inspection was performed approximately 35 hours prior to the accident. The method of inspection requires the mechanic to listen to the assembly during varying speed ranges to detect unusual bearing noise. In addition, a Robinson Safety Notice (#28), requires the pilot to listen during start up and shut down for unusual noises in the upper and lower clutch actuator bearings. According to the safety notice, a failing bearing will produce a whine, rumble, growl, or siren sound. The aircraft was equipped with Teletemp indicator tapes (part numbers 110-2 and 110-4). The tapes are used to track changes in operating temperature. The status of the tapes was checked 1 hour prior to the failure for any trend change. No change was found.