No audio was recorded from inside the cockpit of the C-130 Hercules that crashed while fighting fires in southern New South Wales, killing its three crew members, according to the investigation's initial report.
Investigators had hoped the cockpit voice recorder would provide critical details about what caused the crash that killed United States aerial firefighters Ian McBeth, Paul Hudson and Rick DeMorgan Jr as they battled the Good Good fire near Cooma on January 23.
The recorder was retrieved from the wreckage and, though damaged, its audio recovered.
But Australian Transport Safety Bureau (ATSB) chief commissioner Greg Hood today said audio of the flight had not been recorded.
"Instead, all recovered audio was from a previous flight when the aircraft was operating in the United States," he said.
No distress call made before impact
When releasing its preliminary report into the crash, the ATSB said it had already been able to piece together some of the moments leading to the air tanker's crash.
Witness video showed the aircraft making a number of passes at varying heights before dropping retardant and becoming obscured by smoke.
About 15 seconds after this, it was seen flying "at a very low height" with its left wing down, which then clipped a tree and crashing into the ground.
A review of air traffic control recordings found no distress calls were made by the crew before the impact.
Mr Hood said there would be other methods to determine what caused the accident, but a full review could take more than 18 months.
"Our investigators do have a range of other evidence, including witness videos, at their disposal in building a comprehensive understanding of the accident sequence," he said.
The investigation has yet to consider the aircraft's maintenance history, crew qualifications and environmental influences or complete its teardown and inspection of the tanker's engines and propellers.
But Mr Hood said any critical safety information would immediately be made known to regulators and the public.
