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A Robinson R22 helicopter collided with terrain when it likely encountered a downdraft with insufficient height to recover while unnecessarily flying at low level through the Northern Territory’s MacDonnell Ranges in Australia, an Australian Transport Safety Bureau (ATSB) investigation has found.
The R22 had departed a cattle station’s homestead’s helipad to inspect bore sites and then assist with the recovery of a vehicle at Quartz Hill. After completing a bore inspection, the helicopter took-off and was levelled off at 150 feet above ground level, which was below the peaks of the surrounding terrain as it tracked into the MacDonnell Ranges to continue towards Quartz Hill.
Shortly after entering the MacDonnell Ranges, the R22 collided with the ground on a downslope, about 125 kilometres east of Alice Springs. The helicopter’s last recorded data point indicated it was at about 142 feet above ground level with an estimated ground speed of about 79 knots. The pilot sustained fatal injuries and the passenger was seriously injured.
ATSB analysis of the helicopter’s GPS data and other available evidence suggested the pilot was likely operating the helicopter at low level and possibly contour flying. For the prevailing winds, the helicopter’s final track placed it on the lee side of higher ground. Bureau of Meteorology analysis indicated that broadscale moderate turbulence was especially likely at the time of the accident in the lee of the ranges and as a result of stronger upper winds mixing with lower winds.
ATSB director transport safety, Dr. Stuart Godley, said the investigation determined it was very likely the pilot was operating at low-level when the helicopter encountered a downdraft with insufficient height to recover, leading to the collision with terrain.
“When flying at low altitude there is a lower margin for error for obstacle avoidance. Even if a pilot has been trained and approved to conduct low-level operations it should be avoided when there is no operational need to do so,” Godley said.
The investigation also found a number of other factors that increased risk, including incomplete pre-flight planning, overloading, a forward centre-of-gravity, and the pilot’s elevated blood alcohol level.