What happened

On 27 March 2014 the pilot of a Robinson R22 helicopter, registered VH-HRX, departed from Mullapunyah station, Northern Territory, for a short flight to the north-west. About 10 minutes after departure the pilot radioed that the drive v‑belts had failed and the station owner, in another R22, saw the helicopter enter a steep descent.

Soon after, the station owner found the helicopter complete and upright in a relatively clear area. The pilot of VH-HRX, who was laying a few metres from the helicopter, had sustained a serious head injury. The station owner tended the casualty and alerted emergency services at Borroloola of the accident, as well as personnel at the station homestead. Station personnel accessed the accident site over the rough terrain and started to transport the injured pilot on the back of a utility vehicle. The casualty was later transferred to a Bell 206 Jetranger helicopter for transfer to Macarthur River Mine. An aeromedical service then transported the injured pilot to Darwin where he was hospitalised for a number of weeks.

What the ATSB found

During the initial engine start/clutch engagement process following an extended period of static belt stretching, one or both rotor drive v-belts were displaced on the lower sheave with consequent increase in v-belt slack. Although the pilot, who was not qualified to conduct such maintenance, adjusted the clutch actuator to correct the excessive v‑belt slack, the v-belt displacement went undetected. While being operated in that abnormal configuration, one of the belts weakened and failed with consequent failure of the remaining belt, loss of drive to the rotors, and a forced landing.

Although Robinson Helicopter Company Safety Notice SN-33 provided guidance to pilots on how to stretch new v-belts statically, it did not specifically warn pilots that this process can increase the risk of belt displacement during the subsequent start.

Safety message

This accident highlights that in addition to having a good working knowledge of Robinson Helicopter Company Safety Notice SN-33, R22 pilots and engineers should be especially aware that, if the rotors do not turn within 5 seconds after clutch engagement, it is critical to perform the shutdown procedure and check the slack and position of the v-belts on both the lower and upper sheaves, before flight.

Pilots and operators of helicopters should also consider the residual risk of their operation and the benefit of occupants wearing helmets to reduce the risk of head injury in the event of an emergency landing.