Australian investigators have opened an inquiry into an accident involving a Boeing 737-300 firefighting aircraft near Ravensthorpe in the southwest of the country.

The air tanker came down in the vicinity of Fitzgerald River national park.

Both pilots, the only occupants, survived the 6 February accident, according to the aircraft’s operator, Coulson Aviation.

Coulson had recently been granted a contract to operate the 737 – a 1995 ex-Southwest Airlines jet, converted and designated Tanker 139 – to support Australian firefighters, under a two-year government contract.

It stated that the aircraft (N619SW) would be based in Sydney but support operations elsewhere in the country. The 737 is fitted with a patented aerial delivery system capable of dropping up to 4,000USgal of retardant.

Coulson says the twinjet suffered the accident while “tasked to a fire”, but does not elaborate on the circumstances. It states, however, that the pilots “walked away” and have been medically assessed.

“We are offering all the support we can to our local and international crews,” it adds. “We’re also grateful for the support being provided by our firefighting and aviation industry colleagues in Western Australia.”

The Australian Transport Safety Bureau states that it is gathering a team of investigators from its Perth and Canberra offices, specialisting in operations, maintenance, data recovery and human factors.

It says it intends to interview the crew and other witnesses to understand the circumstances of the accident, and “determine the accessibility” of the site – about 400km south-east of Perth – in order to examine the wreckage.

Western Australia’s Department of Fire and Emergency Services says the aircraft took off from Busselton-Margaret River airport at 15:30 to deal with a bushfire. It states that the accident occurred about 45min later, at 16:15. The pilots removed themselves from the aircraft and were recovered by helicopter.

Coulson Tanker 139-c-Coulson Aviation

Source: Coulson Aviation

Coulson had supplied the aircraft, Tanker 139, to Australia under a new firefighting support contract