Canberra, May 3 : A preliminary report on Wednesday revealed that a Boeing 737 aircraft struck a ridgeline and then crashed during an aerial firefighting task in Western Australia (WA) earlier this year. According to the report released by the Australian Transport Safety Bureau (ATSB), the modified Boeing 737 air tanker, callsign "Bomber 139", departed from Busselton Airport on February 6 with two pilots on board to assist fire control efforts near Hopetoun, a town on the state's south coast, reports Xinhua news agency. "Arriving at the fire ground, the 737 crew was briefed by a bird-dog aircraft that the tasking was to tag and extend an existing retardant line," said ATSB Chief Commissioner Angus Mitchell. The report detailed that Bomber 139 descended to about 400 feet and completed a partial drop of three-quarters of their tank, before the captain stopped the drop as their retardant line was entering a burnt area. The air tanker then repositioned to commence a second drop to use the remaining retardant. "Flight recorder data shows the throttles were advanced and the engines had accelerated just before the aircraft struck a ridgeline with the stick shaker activating. The aircraft then cleared a small line of foliage, before impacting the ground a second time and sliding to rest," said Mitchell. "Fortunately, and remarkably, both pilots were able to exit the aircraft through a cockpit window, and suffered only minor injuries," he added. The aircraft was subsequently consumed in a post-impact fire. The investigation is still ongoing with a final report expected to be released. At about 4.40 p.m. on February 6, police and emergency services responded to reports of a plane crash in the Fitzgerald River National Park. According to WA Police, the aircraft was believed to have taken off at 3.25 p.m. "This is the first serious accident involving a Boeing 737 aircraft in Australia, and the second involving a large air tanker firebombing aircraft," Mitchell said in a statement shortly after the accident. /IANS