MELBOURNE/SYDNEY (Reuters) - Australian officials were working on Friday to extricate the bodies of three U.S. firefighters from a plane that crashed in remote bushland, as the area’s “active” bushfire status complicated an investigation into the accident.

Officials said it was still too early to speculate on the cause of the crash of the C-130 Hercules tanker plane on Thursday, killing its entire crew, just after it dumped a large load of retardant on a huge wildfire in a national park.

“We are very much into the evidence gathering phase of the investigation,” Greg Hood, chief commissioner of the Australian Transport Safety Bureau (ATSB), which is leading the investigation, told reporters. “We will not be speculating.”

However, he added that “we have nothing to suggest there was a systemic fault” when asked whether other aircraft in use were safe.

Coulson Aviation, the Canadian firm that owned the plane and employed its crew, revealed on Friday that all three were former U.S. military members with extensive flight experience: Captain Ian H. McBeth, 44; First Officer Paul Clyde Hudson, 42; and Flight Engineer Rick DeMorgan Jr., 43.

Firefighters in Australia held a minute’s silence and flags on official buildings in New South Wales (NSW) state, where the plane crashed, were flown at half-mast as a mark of respect on Friday.

“We will forever be indebted to the enormous contribution and indeed the ultimate sacrifice that’s been paid as a result of these extraordinary individuals doing a remarkable job,” NSW Rural Fire Service Commissioner Shane Fitzsimmons said at a farewell near Sydney airport for 32 U.S. firefighters who were returning home after weeks on duty on Australia.

ATSB investigators had to be escorted to the one-kilometer-long crash site by firefighters on Friday and police were still in the process of securing the area, Hood said. Little of the plane was intact and potential hazards included aviation fuel and unexploded pressurized canisters, he added. (Graphic: tmsnrt.rs/30O47Eq)

Hood said the ATSB expected to retrieve the plane’s black box cockpit voice recorder, use a drone to 3D map the site, analyze both air traffic control and the plane’s data and review the weather at the time of the crash.

“We understand there were several witnesses to the accident,” he said. “We hope that some of the witness statements will actually be able to shed light on the sequence of events following the dropping of the retardant.”

A team from Coulson Aviation was due to arrive in Australia on Saturday, along with the aircraft history and maintenance records.

Coulson grounded its other large air tankers immediately after the crash but said on Friday they would be returning to work “in the very near future”.

There have been two previous crashes involving C-130 Hercules aircraft while fighting wildfires. In a 2002 accident in California the wings of the aircraft folded upward, breaking off the plane before the fuselage rolled and hit the ground upside down, killing all three crew. In 2012, another C-130 crashed in South Dakota, killing four of the six crew, in an accident that was later determined to be weather-related.

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“Unfortunately, aircraft are one of the riskiest parts of wildland firefighting,” said Eric Kennedy, a disaster and emergency management expert at York University in Toronto, Canada.

Kennedy said there many possible causes for Thursday’s crash, but noted that a well-known risk in the C-130 fleet was metal fatigue-induced wing failure.

“Reduced visibility, high turbulence, and low flying can all be contributing risk factors for air tanker crashes,” Kennedy said in emailed comments.

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MORE U.S. FIREFIGHTERS ARRIVE

The death toll from Australia’s devastating bushfires rose to 33 on Friday after police found a body in a home completely destroyed by fire in New South Wales south coast. The body has not yet been formally identified but it is believed to be of the 59-year-old male occupant, state police said in a statement.

The toll includes eight firefighters.

The fires have also killed millions of animals, razed thousands of homes and destroyed a land area about one-third the size of Germany since September.

Around 250 firefighters from the United States and Canada have undertaken deployments in Australia since the start of the season.

A 41-strong U.S. team arrived in Melbourne from the United States on Friday to help in eastern Victoria, the state’s Country Fire Authority said.

While fire conditions eased in southeastern Australia on Friday, Sydney was choking on a new smoke haze, blown in by a baking hot wind from the fires burning in the south of the state.

In New South Wales, firefighters were tackling 65 blazes with only one at the “watch and act” category, meaning there was no immediate threat. In Victoria state, all 37 fires were rated at the lowest level.