The operator of two R22 mustering helicopters which collided soon after take-off did not define appropriate separation standards for its helicopter operations, with pilots permitted to arrange their own separation, an ATSB investigation has found.
The investigation's final report details that between first light and sunrise on 25 July 2024, the pilots of four Robinson R22s planned to take-off from the Mount Anderson Station homestead in WA's Kimberley to transit to a mustering site about a 10-minute flight away.
Shortly after taking off, two of the helicopters, flown by the lead pilot and another experienced mustering pilot, collided about 150 ft above ground level. The helicopters departed controlled flight and collided with terrain, and both pilots were fatally injured.
An ATSB investigation established that the helicopters collided during initial climb, after the lead helicopter had manoeuvred to the right.
"Neither pilot detected their converging flight paths before the collision," Chief Commissioner Angus Mitchell said.
"While limited data prevented a full visibility study to establish what each pilot could see, the wreckage examination indicated that at the point of collision the lead helicopter may have been in a blind spot for the second helicopter."
The investigation's final report considers what actions the helicopters' operator, Pearl Coast Helicopters, was taking to manage aircraft separation in its operations.
"The tools used by the operator to consider and manage operational risk were not tailored to their main business of aerial mustering," Mr Mitchell said.
"Further, the risk of collision had not been identified in operational risk assessments, and the operator's manuals did not provide documented procedures to ensure pilots establish and maintain adequate separation between helicopters."
Instead, the final report notes, company pilots were permitted to arrange their own separation based on personal preference.
"Pilots routinely flew with reduced vertical and lateral separation, and over time this became an accepted operating preference."
Mr Mitchell said the accident was a demonstration of the need for risk management to identify, assess and mitigate risks.
"Aerial mustering plays a critical role in Australia's agricultural sector," he said.
"This tragic accident should serve as a trigger for all mustering operators to consider their risk management practices, and whether they have scaled them adequately for their operation."
The final report notes Australia's Civil Aviation Safety Regulations for aerial work activities (Part 138) are intended to provide operators with flexibility through scalable risk management practices.
"We encourage operators to review available guidance to assist in their identification and management of hazards."
Mr Mitchell also said the accident was another reminder of the fallibility of see-and-avoid as a primary means of identifying and managing the threat of collision.
"Defined separation minimums and pre-planned safe exits which provide an opportunity to identify and respond to emerging collision threats are important tools in assisting pilots avoid midair collisions," he said.
"Additionally, airframe obstructions can limit visibility in even the most open cabins. This should be a key consideration when establishing how aircraft should be positioned when flying in close proximity."
You can find here the final report: Midair collision involving Robinson R22 Beta II, VH-HQH, and Robinson R22 Beta II, VH-HYQ, 51 km south-south-east of Curtin Airport, Western Australia, on 25 July 2024
