Incident Overview
At approximately 1614 local time, an air tanker operating as Bomber 139 crashed during a firefighting mission in Fitzgerald River National Park, Western Australia. The aircraft had departed from Busselton Airport, Western Australia, on a task to drop fire retardant. There were two pilots on board: the captain in the left seat serving as pilot flying, and a copilot in the right seat as pilot monitoring.
Sequence of Events
During a go-around from a second partial retardant drop, the aircraft impacted a ridgeline at an elevation of about 222 feet. The subsequent crash resulted in a post-impact fire that destroyed the aircraft. Both pilots sustained minor injuries.
ATSB Findings
The Australian Transport Safety Bureau (ATSB) conducted an investigation and released the following probable cause:
"The ATSB found that the accident drop was conducted at a low height and airspeed downhill, which required the use of idle thrust and a high descent rate. The delay in the engines reaching go-around thrust at the end of the drop resulted in the aircraft’s height and airspeed (energy state) decaying as it approached rising terrain, which was not expected or detected by the pilot flying. Consequently, the aircraft’s airspeed and thrust were insufficient to climb above a ridgeline in the exit path, which resulted in a controlled flight into terrain. The operator’s practice of recalculating, and lowering, their target drop speed after a partial load drop also contributed to the low energy state of the aircraft leading up to the collision with terrain. The ATSB also found that the operator and tasking agency had not published a minimum drop height, which resulted in the copilot, who did not believe there was a minimum drop height, not making any announcements about the low energy state prior to the collision. The ATSB found the operator’s pilot monitoring duties were reactive to the development of a low energy state and did not include call-outs either before or at the minimum target parameters to reduce the risk of a low energy state developing. The ATSB benchmarked the WA, New South Wales and National Aerial Firefighting Centre standards against the United States Forest Service and United States National Wildfire Coordinating Group standards and found inconsistencies between the Australian agencies’ standards but not among the United States agencies’ standards. This was likely a result of each Australian state participating in the LAT program independently producing their own standards."