A pilot fell asleep and was uncontactable for 40 mins as his plane flew over Brisbane and the Gold coast, an investigation has found.
The Air Transport Safety Bureau (ATSB) said air traffic controllers lost contact when the plane was around 53 km north-west of Sunshine Coast airport in July 2020, and tried repeatedly to try and get through to the pilot.
The pilot only responded after the plane was over 100km away from its intended destination, and was instructed to head to Gold Coast airport, where he safely landed the plane.
The Cessna 208B Caravan aircraft had originally departed Cairns and was heading to Redcliffe as part of a ferry flight.
The ATSB said they asked the pilot of a Royal Flying Doctor Service Beechcraft B200 King Air to try and intercept the Cessna, and to wake up the pilot.
The King Air pilot at first attempted to attempted to get close and contact the unresponsive pilot, but couldn’t get through.
So he tried dipping the plane’s wings and approached the Cessna in an attempt to trigger its traffic alert and collision system (TCAS), but the pilot remained unresponsive.
Eventually the pilot woke up and was able to re-establish communication with air traffic controllers.
According to the report by ATSB, the pilot had fallen asleep due to fatigue, with the situation likely exacerbated by mild hypoxia from the intermittent use of supplemental oxygen.
The plane was flying at over 11,000 feet due to icy conditions, but the pilot was only occasionally using the supplied oxygen.
The report says the pilot “was experiencing chronic fatigue due to their reported inadequate sleep” and that sleep was inconsistent over an “extended period” prior to the incident.
The ATSB acting transport safety director, Kerri Hughes, said the investigation found the mild hypoxia was making the fatigue worse.
“Operating at 11,000 feet with intermittent use of supplemental oxygen likely resulted in the pilot experiencing mild hypoxia. This likely exacerbated the pilot’s existing fatigue and contributed to the pilot falling asleep.”
Hughes said the incident highlighted the importance of pilots being aware of their condition and health.
“This incident emphasises the importance of pilots monitoring their own health and wellbeing, to ensure that they are well-rested and adequately nourished, especially when conducting single pilot operations.”
Hughes said medical specialists had concluded that the pilot had not lost consciousness solely because of mild hypoxia.
“Although a common symptom of hypoxia is loss of consciousness, it is not typical for someone experiencing hypoxia to regain consciousness, while still operating at the same altitude and without additional oxygen,” she said.
Peter Gibson, a spokesperson for the Civil Aviation Safety Authority, said hypoxia comes when the amount of oxygen in the air drops, and can be fatal.
“Once you get above 10,000 feet or so, the amount of oxygen in the atmosphere decreases to a point where you can’t breathe normally.”
He said most aircrafts are pressurised, so avoid the dangers, but in an unpressurised plane, pilots need access to continuous oxygen.
“Its very insidious, it just creeps up on you. If you don’t get oxygen and drop to a lower altitude, its fatal. No two ways about it.”
Hypoxia was also the main culprit behind the deaths of all eight occupants of a chartered Beechcraft 200 Super King Air which crashed in Western Australia in similar circumstances, in September 2000.