CANBERRA, June 21 (Xinhua) -- A fatal fire surveillance aircraft crash near Cloncurry, Queensland in 2023 was caused by pilot hypoxia brought on by a persistent pressurization system defect, a government investigation report has revealed.

The Gulfstream 695A, operated by aircraft rental service AGAIR was on a mission to map fire zones near Mount Isa on Nov. 4, 2023, when it crashed, killing the pilot and two camera operators on board, according to the Australian Transport Safety Bureau (ATSB).

The ATSB found the aircraft's pressurization system had been unreliable for months, yet AGAIR management failed to formally address the issue. As a result, pilots resorted to unsafe, improvised measures such as brief descents and frequent use of emergency oxygen.

On the day of the crash, the pilot briefly descended from 28,000 to 15,000 feet before returning to cruising altitude. Approaching Cloncurry, a power reduction at 28,000 feet led to a loss of control and a steep spin, with evidence suggesting the pilot was impaired by hypoxia before the fatal crash, said the report released on Thursday.

Air traffic controllers detected signs of hypoxia in the pilot's speech, but AGAIR management failed to inform them of the known defect, preventing timely intervention that might have averted the crash, the report said.

The ATSB identified systemic failures, including normalized unsafe practices and unclear emergency protocols, prompting key actions such as Airservices Australia's revision of hypoxia response procedures, it said.

"This was a tragic and entirely unnecessary accident that underscores the dangers of operational practices which circumvent critical safety defenses, and the insidious and deadly potential of altitude hypoxia," said ATSB Chief Commissioner Angus Mitchell. ■