FTW03LA099 · Robinson R22 Beta II

While ferrying a helicopter to its new owner/operator, the 1,351-hour pilot experienced a loss of main rotor drive. The pilot reported that the helicopter was in level cruise flight at an altitude of 700 to 900 feet AGL at an indicated airspeed of 70 to 75 knots, when they heard a loud "thump" coming from the area behind the cabin, immediately followed by the activation of the clutch light and accompanied with a change in engine and rotor noise. Within a couple of seconds, the pilot reported hearing another "thump" and, subsequently, the engine RPM started to increase as the rotor RPM was decreasing. The pilot initiated a 180-degree turn to position the helicopter into the wind while maintaining 70 knots as he entered an autorotation into rolling rough and uneven terrain. The helicopter came to rest in an upright position. Examination of the wreckage by the FAA inspectors, who traveled to the accident site, revealed that both main rotor blades were damaged and the tailboom was severed from the helicopter and broken into several pieces consistent with the main rotor contacting the tailboom during the landing. The engine showed evidence of an overspeed greater than about 110%. One of the two drive belts was missing and the remaining belt was off of the upper sheave and showed considerable damage. The wreckage was recovered to the Robinson Helicopter Company facility in Torrance, California, for a detailed examination. No discrepancies were noted, apart from impact related damage, in the assembly, installation or alignment of the engine, clutch assembly or actuator assembly. No evidence of pre-impact damage to the flight and powerplant controls was found. The failed belt was found separated between the vees with only a 5-inch section still intact.

Verbatim NTSB analysis and probable cause from the NTSB dataset