Enroute from Curtain Springs to Alice Springs, while flying low and slow to observe cattle, the pilot heard a loud noise followed by an immediate increase in engine RPM and decrease in rotor RPM. An autorotational approach and landing was carried out into the rough hilly terrain, but the helicopter landed heavily and rolled over. A subsequent investigation revealed that the clutch assembly upper bearing had failed allowing the engine drive to disconnect from the rotor system. The bearing was a commercial bearing, not a genuine Robinson bearing, although the manufacturer's instructions clearly state that only genuine bearings, having the correct internal clearances, must be installed. A specialist report indicated that the failure was due to brinelling of the bearing races, possibly caused by the bearing being dropped or damaged during assembly of the clutch. There was also evidence that the bearing had not been sufficiently lubricated which would have decreased its time to failure. Although the accident was survivable, severe spinal and lower back injuries were suffered by both occupants. It was reported that the space below the seats contained a number of hard items including a hand fuel pump. The flight manual for this type of helicopter, and placards placed near the under seat compartments caution against placing hard objects in them as they could cause injury to occupants if the seats crush while absorbing energy during a heavy landing. SAFETY ACTION As a result of the investigation, the Civil Aviation Authority issued Airworthiness Directive AD/R-22/39, which requires an inspection of the upper clutch actuator bearing of all R22 helicopters to ensure only approved parts are fitted.