SYDNEY (REUTERS) – A C-130 tanker plane that crashed and killed all three Americans on board while fighting fires in Australia in 2020 likely stalled when flying in hazardous conditions after making a fire retardant drop, investigators said in a final report on Monday (Aug 29).

The Australian Transport Safety Bureau (ATSB) said it had identified a number of safety recommendations for large air tanker firefighting operations after the crash of the Lockheed Martin Corp plane, operated by private Canadian firm Coulson Aviation under contract to the New South Wales Rural Fire Service (RFS).

Coulson did not provide a pre-flight risk assessment tool for its firefighting large air tanker crews, ATSB said, while RFS had limited policies for aerial supervision requirements and no procedures for deploying tankers without aerial supervision.

In this case, a lead aircraft called a “birddog” initially assigned to support the C-130 had declined the mission due to weather-related safety concerns, but there is no evidence that was communicated to the tanker crew, ATSB said.

ATSB Chief Commissioner Angus Mitchell said the responsibility for the safety of aerial firefighting operations needed to be shared between the tasking agency and the aircraft operator.

“This accident highlights the importance of having effective risk management processes, supported by robust operating procedures and training to support that shared responsibility,” he said in a statement.

Coulson has since taken pro-active safety measures in response to the accident, including the introduction of a pre-flight risk assessment tool and new windshear management procedures and training, Mr Mitchell said.

The RFS has also committed to undertake research into best practices in aerial supervision procedures and task rejections, he added.

The crash of the plane killed US military veterans Captain Ian McBeth, 44, of Great Falls, Montana, First Officer Paul Clyde Hudson, 42, of Buckeye, Arizona, and Flight Engineer Rick DeMorgan Jr, 43, of Navarre, Florida.

The three US firefighters were a part of a multi-national team that had been helping Australia combat devastating bush fires.

The cockpit voice recorder was recovered but investigators said the data was not useful because all of the audio was from a flight that was operated in the United States in 2019.

The aircraft had been based there before coming to Australia to help during a bushfire season that killed 33 people, charred nearly 12 million hectares (29.7 million acres) of land and wreaked billions of dollars in damage.