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Hypoxia possible cause of fire surveillance crash

written by Adam Thorn | February 7, 2024

Overview of the accident site (Queensland Police, ATSB)

The ATSB is investigating whether hypoxia was responsible for a twin turboprop Commander crash that killed three people conducting aerial fire surveillance last year.

In its preliminary report into the incident in Queensland’s remote northwest, air crash investigators said voice recordings showed the pilot’s rate and volume of speech had “substantially lowered”.

Hypoxia is the result of a lack of oxygen in the body tissues. The most common type of hypoxia in aviation is altitude (hypobaric) hypoxia, which can be prevented by pressurising the aircraft or by breathing supplemental oxygen.

Symptoms can be insidious and include sleepiness, drowsiness, slurred and slowed speech, confusion and impaired cognition and decision making.

The ATSB’s chief commissioner, Angus Mitchell, said, “During their on-site examinations, investigators were able to account for all major aircraft components and determined that both engines and propellers had indications that the engines were running at impact.


“However, it was not possible to determine the operability of the aircraft’s pressurisation and oxygen systems.”

The preliminary report details that the aircraft, operated by AGAIR under contract with Queensland Fire and Emergency Services, had taken off from Toowoomba to photograph fire zones north of Mount Isa. On board were a pilot and two camera operators employed by the operator.

About 20 minutes after reaching the planned cruise altitude of 28,000 ft, the aircraft descended to 15,000 ft, remaining there for about 6 minutes before returning to 28,000 ft. After another 25 minutes, the air traffic controller requested the pilot change the radio frequency.

“The pilot acknowledged this request, but the controller was then unable to establish two-way communications with them for over an hour,” Mitchell said.

Once communications were eventually re-established, the pilot advised the controller they were to conduct airwork in an area near Mount Gordon.

When they were provided clearance for this, the pilot, seeming uncertain, repeated the clearance four times over four minutes.

“Although a formal speech analysis has not been undertaken at this stage, radio recordings during this period indicate that the pilot’s rate and volume of speech had substantially lowered from earlier communications and was worsening,” Mitchell noted.

Flight data indicates approximately 20 minutes after the pilot’s last transmission, the aircraft’s ground speed decreased before it departed controlled flight and began to descend rapidly.

The aircraft crashed in flat, open bushland and was destroyed by a “significant” post-impact fire.

Along with work at the crash site, ATSB investigators have also interviewed relevant parties, collected radio communication recordings, aircraft tracking and navigational application data, and gathered documentation relating to the aircraft, pilot, crew and operator.

“As the investigation proceeds, it will include further analysis of the pilot’s speech during radio communications, including an examination of hypoxia indicators,” Mitchell said.

“Investigators will also analyse weather information, maintenance records, operational procedures, flight data, and pilot and crew training and medical records.”

A final report will be released after the investigation.

“If at any time should a critical safety issue identified during the course of the investigation, the ATSB will immediately notify relevant parties so safety action can be taken,” Mitchell concluded.

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