Hypoxia strikes over Queensland

A Reims-Cessna F406 Caravan II, similar to the one involved in the Hypoxia event. Image: Pedro Aragão CC BY 3.0

It’s often said in aviation, that safety is about getting the little things right. This modest saying was borne out last year, when a routine aerial survey flight over Queensland turned hypoxic when a simple oxygen supply fitting disconnected at 18,000 feet.

The full report, released by the Australian Transport Safety Bureau (ATSB), details how the pilot became confused during the initial climb after noticing his blood oxygen saturation had fallen well below expected levels.

Unsure of what was causing the disruption, the pilot notified the navigator of the issue and tried to increase oxygen via the system’s controller.

The navigator, who had undergone hypoxia awareness training, moved closer to the pilot to provide assistance and monitor the pilot’s condition.

As the twin turboprop Reims Aviation F406 continued to climb, the pilot’s ability to handle the aircraft diminished and he failed to heed warnings from his navigator to maintain control of the aircraft and descend to a lower altitude.

The oxygen port beneath pilot's armrest. Image: ATSB
The oxygen port beneath pilot’s armrest. Image: ATSB

The pilot, who was probably hypoxic at this point, also failed to respond to multiple to air traffic control (ATC) transmissions, and when he finally did, his responses ‘were non-standard and his speech was slurred.’

Upon hearing the pilot’s responses, ATC transmitted ‘ oxygen, oxygen, oxygen’ and cleared the pilot to descend—declaring ALERFA alert phrase in the process.

Amazingly, despite his hypoxic condition, the pilot was able to determine the issue with his oxygen system, identifying that the system’s supply fitting had become disconnected.

The pilot re-connected the fitting and after taking a number of deep breaths felt immediate relief, quickly recovering from his confused state.

The pilot commenced a controlled descent and remained on oxygen until landing at Emerald, at which point he noticed his oxygen saturation levels had returned to normal.

The operator’s report into the incident found that ‘the bayonet fitting may not have been fully locked when connected by the pilot, noting that the connection could be in place but not necessarily properly locked.’

The associated oxygen fitting that disconnected. Image: ATSB
The associated oxygen fitting that disconnected. Image: ATSB

The investigation report also added that ‘the position of the port is such that some concentration and manipulation is required to ensure that the connection is seated correctly’ and that ‘the supply tube may not have been correctly routed through an armrest cut-out, and that movement of the armrest may have dislodged the improperly secured bayonet fitting.’

The operator’s report also found that ‘the pilot’s oxygen controller was not visible to the pilot or navigator’, which meant the crew ‘were unable to see indications on the controller that could have alerted them to an oxygen supply problem.’

While the ATSB didn’t recommend specific safety actions arising from the incident, it did reiterate the importance of paying careful attention to aircraft oxygen systems, particularly when connecting and monitoring system performance.

The ATSB concluded:

 Hypoxia is dangerous because it impairs cognitive and physical performance, sometimes without the flight crew realising that anything is wrong. Sudden onset may require a rapid and instinctive response by aircrew whereas gradual onset is a matter of awareness so that an appropriate response can be made before incapacitation occurs.

Flight Safety Australia examined Hypoxia in 2013 and analysed the harsh realities of the insidious killer and also created a training video highlighting these affects.


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