Australia's air safety watchdog has recommended national safety standards and minimum drop heights for water bombers as it wraps up its investigation into the crash of a large air tanker in Western Australia.
The Boeing 737 water tanker crashed on February 6, 2023, while dropping fire retardant on a bushfire in the Fitzgerald River National Park, 460 kilometres south-east of Perth.
The plane clipped a ridge before crashing into the ground.
Both pilots escaped with minor injuries in what then-WA Premier Mark McGowan described as a "miracle".
The Australian Transport Safety Bureau (ATSB) released its final report on its investigation into the accident on Wednesday.
LoadingIt found the aircraft struck a ridge line during a second drop onto the bushfire before hitting the ground a second time and sliding to a stop.
The pilots were able to escape through a cockpit window before the aircraft went up in flames.
A computer-generated recreation of the crash shows the flights final moments as it descends.
The burnt out remains of the plane crashed while fighting a bushfire near Hopetoun. (Supplied: DFES)
Bomber flying too low
ATSB chief commissioner Angus Mitchell said the bomber was flying low and slow to complete a drop to extend a fire retardant line.
"Towards the end of the drop, the aircraft's height and airspeed decayed as it approached rising terrain that had not been detected, and was not expected, by the aircraft captain," he said.
"Not detecting the rising terrain likely contributed to the captain allowing the aircraft to enter a low energy state during the drop."
The plane appeared to have crashed on an unsealed road in the Fitzgerald River National Park. (Twitter: PilotPoli)
The report noted captains could use their own judgement on drop heights as operator Coulson Aviation and the WA government had not published a minimum limit.
"This resulted in the co-pilot, who did not believe there was a minimum drop height, not making any announcements about the aircraft's low energy state prior to the collision," Mr Mitchell said.
While Coulson Aviation had a standard minimum drop height of 150 feet [45 metres], it was not published in the operations manual.
LoadingSince the accident, Coulson Aviation has increased its minimum drop height of 200 feet [61 metres] for large air tankers.
WA's Department of Fire and Emergency Services and the Department of Biodiversity, Conservation and Attractions are amending procedures to implement a 200 feet [61 metres] minimum height.
The two pilots, believed to be Canadian, were able to walk into hospital after the crash. (ABC News)
The ATSB investigation also identified the variation of standard operating procedures between state as a safety issues which increased risk.
Rules to be standardised
The Australasian Fire and Emergency Services Authorities Council will now develop standard operating procedures for large air tankers at a national level.
The remote Fitzgerald River National Park has a number of rugged peaks. (Supplied: WA Parks and Wildlife Service)
"This accident highlights that standard operating procedures and crew resource management should be implemented with the intent to prevent an unsafe situation from developing," Mr Mitchell said.
"Safety standards should not be solely dependent on the performance of the pilot flying and recovery call-outs."