What happened

On 12 November 2015, a pilot was mustering cattle in a Robinson R22 helicopter, registered VH-HWJ, at a property about 90 km south of McArthur River Mine, Northern Territory.

At about 1400 Central Standard Time (CST), as the helicopter approached the cattle yards, it descended rapidly and collided with a tree and terrain. The helicopter landed on its side and sustained substantial damage (Figure 1). The accident occurred about 200 m prior to the cattle yards. The pilot sustained serious injuries and was unable to recall the sequence of events.

Figure 1: Accident site showing damage to VH-HWJ

Source: Helicopter operator

Analysis of fractured yoke

The yoke connecting the clutch shaft to the rearward flex plate was found to have fractured at the connection to the shaft (Figure 2). The ATSB conducted analysis to determine whether the yoke failure may have contributed to the accident, or occurred as a result. The analysis found no evidence of fatigue damage in the yoke, and no other signs of pre-existing damage. The helical fracture was consistent with torsional overstress inducing failure in the yoke.

Figure 2: Fracture surfaces

Source: ATSB

Weather

The weather at McArthur River mine was recorded at 1200 and 1530. At 1200, the wind was from 340° at 5 kt and the temperature was 36 °C. At 1530, the wind was from 160° at 4 kt and the temperature was 38 °C. The direction of the helicopter relative to the wind at the time of the accident could not be determined. The ambient temperature at the time of the accident was about 37 °C. Although the influence of the temperature on the accident is unknown, high ambient temperatures adversely affect helicopter performance.

Operator comments

Subsequent to a previous accident, the operator mandated the wearing of helmets for all pilots. The operator commented that although the pilot sustained head injuries, the outcome might have been worse if the pilot had not been wearing a helmet.

ATSB comment

The ATSB was unable to determine the cause of the accident.

Safety message

US military research^[1] analysed helicopter accidents that were at least partially survivable. It found that occupants not wearing a protective helmet were significantly more likely to sustain severe and fatal head injuries. The US National Transportation Safety Board (NTSB) also acknowledged that the use of head protection can reduce the risk of injury and death. The NTSB issued Safety Recommendation A-88-009, recommending that crewmembers of emergency medical services helicopters wear protective equipment including helmets.

The ATSB investigation report (AO-2014-058) into an accident involving a Robinson R22 helicopter where the pilot sustained a serious head injury, reminded pilots and operators to consider the benefit of occupants wearing helmets to reduce the risk of head injury in the event of an emergency landing.

__________

1. Crowley, J.S. (1991) Should Helicopter Frequent Flyers Wear Head Protection? A Study of Helmet Effectiveness. Journal of Occupational and Environmental Medicine, 33(7), 766-769.