On 1 August 2014, at about 0935 EST, a Reims Aviation F406 aircraft, registered VH-EYQ, departed Emerald, Queensland, on an aerial survey task with a pilot and navigator on board. The aircraft was fitted with an oxygen system to allow unpressurised operations above 10,000 ft. The pilot tested the oxygen system for normal operation prior to the flight.
During the climb, the pilot turned on the aircraft oxygen supply and connected and donned his oxygen mask. The pilot then monitored his blood oxygen saturation level on an oxygen pulse meter as the aircraft continued to climb, and monitored his flow of oxygen by reference to a flow indication in the supply tube. All appeared normal until about flight level 180, when the pilot noticed that his blood oxygen saturation level had fallen significantly.
The pilot attempted to increase the amount of oxygen he was receiving by making an adjustment to his oxygen system controller, but the accuracy with which he was controlling the aircraft deteriorated, and his speech became slurred. The navigator encouraged the pilot to maintain control and descend, and air traffic control prompted the pilot to ensure that he was receiving an adequate supply of oxygen. The pilot was ultimately able to reconnect a fitting in his oxygen supply system that had become disconnected. When he reconnected the fitting, the pilot sensed almost immediate relief and was able to make a controlled descent. The crew returned to Emerald for an uneventful landing.
This incident highlights the importance of careful attention to aircraft oxygen systems, particularly with respect to connecting and monitoring oxygen system performance. Pilots are reminded that hypoxia is an insidious condition and the time of useful consciousness is often very limited. A prompt and decisive response to the first indication of an oxygen supply problem is imperative.