An aerospace engineering expert has described the way a Boeing 737 Fireliner crashed in Western Australia's south as "similar" to how another large air tanker crashed in New South Wales in 2020.
The Fireliner crashed while battling two bushfires near WA's south coast on Monday, with the two pilots on board managing to escape with minor injuries.
The Boeing 737 had been converted by Coulson Aviation from a commercial liner into a water bomber.
In January 2020, another Coulson Aviation aircraft was involved in a fatal crash where three American firefighters died during the Black Summer Fires in NSW.
Similarities in radar data
University of New South Wales senior aerospace design lecturer Dr Sonya Brown said the radar data from the latest crash somewhat resembled the data from the fatal crash in 2020.
"Obviously the investigation is in its very early stages, but we can already see the radar data of this aircraft," she said.
"The situation started with a situation at very low altitude … In 2020, the aircraft had just done a [retardant] drop and had tried to climb out of that, and it's believed that part of the problem was a stall on the left wing," she said.
"Unfortunately, stalls at low altitude can absolutely be fatal."
Dr Brown said she suspected the latest crash in WA was likely caused by a similar situation, where conditions meant the aircraft's wings couldn't generate enough lift to climb.
"Coulson [Aviation] updated all of their safety procedures, some of their pilot training, etcetera, to try and avoid such an incident in the future. Yet, here we are just a few years later and we've had another incident," she said.
An investigation into the Black Summer Fires fatal crash found the NSW Rural Fire Service failed to pass on crucial information to the crew of the large air tanker, a C-130, before the crash.
Crash investigation ongoing
The Australian Transport Safety Bureau (ATSB) and the Department of Fire and Emergency Services (DFES) are both conducting separate investigations into the latest crash in WA.
ATSB Chief Commissioner Angus Mitchel has said it would take some time to piece together exactly what happened.
"What we will try and get a very good understanding of [is], was there anything mechanical behind this? Was it in the tasking involved? Was it the environment involved?" he said.
"In this particular instance, it does look as though it's potentially clipped the ridge line and has pancaked down."
Coulson Aviation temporarily grounded its air tankers across the country on a "stand-down day for welfare to rest the teams".
In a statement, Coulson Group CEO Wayne Coulson said they were "not in a position to speculate or make further comment at this time" regarding the cause of the crash.
More aviation incidents likely, expert says
The fact both pilots on board the converted Boeing 737 survived the crash was described as a "miracle" by WA's Premier Mark McGowan. Dr Brown agreed.
"I think we are very, very lucky in this particular accident that the pilots are walking away," she said.
Dr Brown said more work needed to be done to ensure proper assessments of environmental factors were completed before air tankers were deployed, especially as they were being used more frequently to combat bushfires.
The Boeing 737 which crashed on Monday had dropped just under 400,000 litres of retardant on eight bushfires in the last few weeks.
"That's the key thing we can do is better assessment of the local conditions to stop a [retardant] drop, which could be too hazardous," she said.
"We do expect to see, unfortunately, an increase in incidents just because ... we're doing more of this work."
Bushfire response hampered
The fire the pilots were working to control is continuing to burn through large swathes of sensitive bushland in the Fitzgerald River National Park.
More than 4,000 hectares has been burnt since lightning started the fire on Monday.
A watch and act alert in place as firefighters work to protect a handful of private properties in the area.
Firefighters said the loss of the 737 and another, now temporarily grounded large air tanker, was a setback.
"It has certainly initially hampered our response efforts," incident controller David Meehan, from the Department of Biodiversity, Conservation and Attractions, said.
"But I'm comfortable that we've got the six fixed-wing aircraft and the Blackhawk helicopters available to us for any aerial fire suppression."
Investigators from the ATSB will be briefed on the fire ground and safety requirements when they arrive later today.
An exclusion zone has been set up around the crash site, with mineral earthworks and roads closed to protect and preserve the area.
Mr Meehan was confident containment lines should be built around the fire before the end of the day and was hopeful any outbreaks could be held.
