By Matt Bungard and Eilidh Mellis
Three American firefighters have died after a C-130 water tanker aircraft crashed while battling a blaze in southern NSW on Thursday.
ACT Emergency Services confirmed the large air tanker crashed while fighting a blaze near Cooma, north-east of the Snowy Mountains.
A C-130 Hercules, nicknamed Thor, shows its capabilities in 2017.Credit: Ben Rushton
"It's just a ball of flames ... over," a nearby plane said in radio communications with flight control.
Firefighters remain on the ground after the plane crashed in what Rural Fire Service Commissioner Shane Fitzsimmons described as "a large fireball associated with the impact of the plane as it hit the ground", in an area that remains an active fireground.
"Our thoughts are not just with family and loved ones, but for anyone who feels impacted by what has unfolded this afternoon," he said. "We can't thank enough people who continue, notwithstanding the conditions, to put their safety at risk to protect lives and property of others."
Premier Gladys Berejiklian said: "Today again demonstrates the fire season is far from over." She later tweeted that flags would fly at half-mast around the state on Friday.
Mr Fitzsimmons said that Coulson Aviation, the Canadian operator of the C-130 aircraft, had grounded its fleet on Thursday afternoon as a mark of respect for the victims and to reassess safety conditions.
"Obviously, grounding of a number of aircraft momentarily will have an effect on our aerial capacity, but it's absolutely warranted and I support them 100 per cent in grounding them for the reasons that they stipulated," he said.
The missing plane was a re-purposed C-130 Hercules, built in 1981 in America by Lockheed Martin. It took off from Richmond RAAF base at 1pm, and disappeared from the flight radar just after 2pm.
The Commissioner said that the addition of large air tankers had given the RFS capability and capacity that they "simply haven't had before".
He said that the cause of the crash was not yet known. He would not publicly identify the victims, who are all American, until families have been notified.
The owners of Coulson will be on the first available flight out of Canada and are expected to be here within 24 hours, Mr Fitzsimmons said.
He and Emergency Services Minister David Elliott will brief crews from the United States and Canada who have been recently deployed to NSW on Friday morning.
"As the Premier indicated, it is a confronting and sobering reminder of the inherent risks associated with firefighting and we've seen all too often this season, unfortunately, the tragic consequences that can come as a result of these significant bushfires that we've seen burning across NSW," Mr Fitzsimmons said.
People are seen embracing at Numeralla Rural Fire Brigade near the scene of a water tanker plane crash.Credit: Getty Images
He praised the trio as "absolute professionals" and valued members of the firefighting fraternity.
The Australian Transport Safety Bureau is deploying a team of transport safety investigators with experience in aircraft operations, maintenance and data recovery to the accident site, to begin the evidence collection phase of the investigation. A preliminary report will be released in about 30 days.
"The crew on board were well known, not just to their colleagues here in Australia, but we're also reminded that a number of our US colleagues that are embedded in some of the incident management teams right now, including down in the high country, actually had personal relationships with them," Mr Fitzsimmons said.
"Our hearts are out with all those that are suffering what is the loss of three remarkable well-respected crew that have invested, you know, so many decades of their life into firefighting and fire management, and are professionals in the aviation firefighting sector."
Coulson Aviation is a privately owned family company based in Canada. The Coulson family released a statement saying that "thoughts and prayers are with the families of the three crew members onboard".
The US Ambassador to Australia, Arthur B. Culvahouse Jr, issued a statement on Thursday evening.
"I am deeply saddened by the tragic news we received today. The brave Americans who died near Snowy Monaro died helping Australia in its time of need," he wrote on Twitter.
"The families and friends of those who we have lost are in our thoughts and prayers. Thank you Australia for your sympathy and solidarity."
Helicopters and an air force plane circled the Snowy Monaro region after contact was lost with the large air tanker which was working on bushfires in the area.
A Boeing P-8 air force plane, which according to the Australian Defence Force is "a cutting-edge maritime surveillance and anti-submarine aircraft," had been circling an area near Cooma, north-east of the Snowy Mountains.
The Adaminaby Complex fire was burning at emergency level in the region before being downgraded to "watch and act", while visibility remains low due to bushfire smoke.
At a C-130 Hercules demonstration water drop in 2017, then NSW Minister for Emergency Services Troy Grant said, "this aircraft can dump 15,000 litres of water or fire retardant at a time and will be used for direct attacks on both bush and grass fires, to create containment lines, and to provide urban interface protection".
The RFS has a handful of its own aircraft but the vast majority of its aerial efforts are organised through contractors. Two weeks ago, a contracted helicopter crashed into a dam near the border with Victoria.
The RFS uses hundreds of contracted machines to assist in firefighting efforts, although many of them badge themselves with the RFS insignia while associated with the organisation.