Collision with terrain involving a Robinson R44, VH-HLB, 126 km east-south-east of Tindal Airport, Northern Territory, on 23 September 2014

On 23 September 2014, at about 1500 Central Standard Time, a Robinson R44 helicopter, registered VH-HLB, departed Bulman camp, Northern Territory, to conduct gravity survey operations. On board were a pilot and a geophysical field technician. The operation involved flying to specified locations 2 km apart and selecting a suitable landing site within 400 m of the location.

At about 1630, after completing landings at about 30 sites, the helicopter arrived overhead a specified location. The pilot identified a potential landing site, overflew it to more closely assess the site and then entered an out-of-ground-effect hover just above treetop height to determine whether the selected site was suitable for landing. The pilot decided the site was unsuitable as trees prevented sufficient clearance for the main and tail rotors.

As the pilot attempted to depart the area, the helicopter started to sink and the pilot observed the rotor revolutions per minute (RRPM) decaying. He lowered the collective and rolled on throttle in an attempt to increase the RRPM. The outside air temperature gauge indicated about 40 °C and the pilot reported that increasing the throttle did not provide any detectable increase in power. The pilot then eased forward on the cyclic. The helicopter continued to descend and the main rotor blade collided with multiple tree branches. When at about 6 ft above ground level, the helicopter rotated about 180° and landed hard with the left skid touching the ground first. The helicopter sustained substantial damage and the pilot and passenger were uninjured.

This incident highlights the effect of air temperature on aircraft performance. Understanding the controllability issues at the limits of the normal operating envelope can assist pilots in recognising the symptoms of reduced aircraft performance.

Aviation Short Investigations Bulletin - Issue 37