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Pilot Fell Asleep for 40 Minutes Due to Hypoxia

A small aircraft pilot in Australia fell asleep for around 40 minutes mid-flight due to fatigue, lack of sleep, and mild hypoxia, according to The Guardian report last month. 

The air traffic control lost contact when the Cessna aircraft flew over Brisbane and the Gold coast in July 2020, prompting authorities to ask a Beechcraft B200 King Air pilot of the Royal Flying Doctor Service to intercept the Cessna which originally departed Cairns and was heading to Redcliffe. 

The King Air pilot approached the Cessna several times in an attempt to trigger its traffic alert and collision system, but the pilot remained asleep.

After being asleep for around 40 minutes and overflying by more than 110 km from his intended destination, the Cessna pilot finally responded, although air traffic control officials reported that he sounded “groggy.”

The authorities instructed the pilot to head to Gold Coast airport where he could land. At 18:01, he landed safely and was immediately attended to by the aircraft rescue and firefighting officers. However, he declined first aid and an ambulance.

 

Inadequate Sleep and Fatigue as the Main Culprits 

Investigators have suggested that the pilot had fallen asleep due to fatigue and lack of sleep, with mild hypoxia possibly exacerbating the situation.

The reports showed that the Cessna pilot was flying at over 11,000 feet in icy conditions and only used the supplied oxygen intermittently. 

Air Transport Safety Bureau director Kerri Hughes said the incident highlighted the importance of pilots making sure that they are “well-rested and nourished,” which is particularly important during a single-pilot operation. 

The aviation safety officer added that mild hypoxia was likely a secondary factor and not the main culprit because it is not typical for a person experiencing “clinical hypoxia” to regain consciousness without additional oxygen and change in altitude.  

Hypoxia Risk

In general, hypoxia occurs when pilots are flying at high altitudes (i.e., above 12,500 feet) in an unpressurized aircraft. As altitude increases, the air becomes less dense which means less oxygen for breathing. 

While 12,500 feet is the benchmark, some people may experience mild symptoms at altitudes as low as 10,000 feet due to age, fatigue, physical conditions, fitness, smoking, etc. This is probably the reason why the Cessna pilot fell asleep, even though he was only flying at around 11,000 feet. 

Meanwhile, common symptoms of hypoxia, which often appear gradually, are visual impairment, impaired judgment, loss of consciousness, headache, blue lips and fingernails, and even euphoria, which is the earliest and arguably the most dangerous symptom because it can mislead amateur pilots into thinking that everything is okay. 

Pilots are trained to identify symptoms of hypoxia and address the problem to prevent accidents. 

  • According to FFA’s oxygen requirement, pilots must use supplemental oxygen at an altitude above 12,500 feet msl cabin pressure for more than half an hour; and anytime once they reach 14,000 feet msl. 
  • If the pilots think they are getting hypoxic, they can declare an emergency and descend or reduce their altitude below 10,000 feet from the air traffic control. 
  • Small aircraft pilots can inform their passengers in the cockpit about the telltale signs of hypoxia to prevent accidents and keep an eye on each other at high altitudes.
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