Pilot Falls Asleep During Flight, Misses Destination by Nearly 70 Miles

A pilot in Australia was reported to have fallen asleep midflight "likely due to a combination of fatigue and mild hypoxia [lack of sufficient oxygen]," according to the latest report Wednesday by the Australian Transport Safety Bureau (ATSB).

A new ATSB probe into the incident, which took place in July 2020, found the pilot who "was unresponsive to air traffic control calls for 40 minutes had fallen asleep due to fatigue likely exacerbated by mild hypoxia from the intermittent use of supplemental oxygen," the report said.

The pilot woke up and contact was reestablished when the plane was "about 111 km [around 70 miles]" from the intended destination of Redcliffe. The plane instead landed safely at Australia's Gold Coast Airport, around 56 miles south of Brisbane, the bureau said.

The pilot was operating a Cessna 208B Caravan aircraft on an afternoon ferry flight from the city of Cairns to Redcliffe (a suburb of the Brisbane metropolitan area) in the Australian state of Queensland.

The aircraft was cruising at 10,000 feet when the pilot faced "unforecast icing conditions and poor visibility due to cloud." Climbing to 11,000 feet, the pilot began using the plane's supplemental oxygen system intermittently, according to the report.

"Pilots are required to continuously use supplemental oxygen when flying unpressurised aircraft, such as the Caravan, when flying above 10,000 feet," the report explained.

According to the latest ATSB investigation, air traffic control (ATC) was unable to make contact with the pilot when the plane was around 33 miles from the Sunshine Coast Airport, located around 56 miles north of Brisbane.

After several calls, ATC called on pilots in nearby aircraft to help contact the Caravan pilot "who was seen to overfly Redcliffe and track towards Brisbane," the report said.

The report says another aircraft attempted to approach the Caravan to try to trigger the traffic alert and collision system but there was still no response from the pilot.

After 40 minutes without contact, the pilot woke up at 5:35 p.m. local time and ATC communications were reestablished when the plane was "about 111 km [around 69 miles] south-south-east of the intended destination," the report said.

The pilot was instructed to land at Gold Coast Airport where the plane landed safely just after 6 p.m. local time.

ATSB Acting Transport Safety Director, Kerri Hughes, said in the report: "The ATSB found that the pilot was likely experiencing a level of fatigue due to inadequate sleep the night before and leading up to the incident."

Most people tend to "underestimate their level of fatigue and tend to overestimate their abilities," Hughes noted in the report.

"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."

The director said the investigation "carefully considered the role of hypoxia" in the latest case.

She explained: "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.

"Therefore, from the information obtained by a medical specialist engaged by the ATSB and from studies conducted on mild hypoxia at moderate altitudes, the ATSB determined that it was unlikely that the pilot had lost consciousness solely due to mild hypoxia.

"Rather, the pilot had fallen asleep likely due to a combination of fatigue and mild hypoxia, possibly exacerbated by dehydration and diet," Hughes said.

According to an article on the U.S. Federal Aviation Administration (FAA) website, hypoxia is defined as "the lack of sufficient oxygen in the blood, tissues, and/or cells to maintain normal physiological function."

The most common causes of hypoxia in aviation include "flying, non-pressurized aircraft above 10,000 ft without supplemental oxygen, rapid decompression during flight, pressurization system malfunction, or oxygen system malfunction," the article notes.

"One factor that makes hypoxia dangerous is its insidious onset; your signs and symptoms may develop so gradually that they are well established before you recognize them. Hypoxia is painless, and the signs and symptoms vary from person to person," the FAA website explains.