Ethiopian Airlines has suspended two passenger jet pilots following reports they fell asleep midway through a flight on Monday, causing them to overshoot their runway and miss their landing window.
The sleeping pilots were unable to be reached by air traffic control, but were eventually woken by an alarm when the autopilot system disconnected, according to aviation news site The Aviation Herald.
They were able to circle back and safely complete their landing at Ethiopia's capital, Addis Ababa, 25 minutes later.
Flight tracking data confirmed the plane, a Boeing 737-800 flying out of Khartoum in nearby Sudan, was following the correct route as it approached Addis Ababa for landing but didn't descend, instead remaining at its cruising altitude of 37,000 feet (11.2 kilometres).
Ethiopian Airlines said on Saturday that the pilots had been "removed from operation pending further investigation".
"Appropriate corrective action will be taken based on the outcome of the investigation," the airline said on social media.
"Safety has always been and will continue to be our first priority."
Keith Tonkin, managing director of Australian aviation consultancy firm Aviation Projects, said airlines generally have protocols in place to ensure someone at the controls is awake at all times.
However, he said they would rarely need to be enacted for a two-hour flight such as the trip from Khartoum to Addis Ababa.
"It's important [the pilots] be given a chance to explain themselves, but if there was some reason they couldn't stay alert or awake for such a short trip, if they did violate some sort of rule or procedure, then there may be some action taken against them," he said.
"Fatigue management has also become more and more important as airlines have tried to maximise their crew resources, using risk management to optimise the crew to fly as many hours as they can."
Ethiopian Airlines, Africa's largest passenger airline, is generally considered by experts to have a good safety record, and runs its own flight school, the Ethiopian Aviation Academy.
A 2019 crash which killed 157 people shortly after one of the airline's flights took off from Addis Ababa was found to be the result of faulty sensors and new anti-stalling software in Boeing's 737 MAX 8 jet, the same flaws which led to the crash of Lion Air Flight 610 in Indonesia in 2018 and ultimately the jet's temporary grounding.
Boeing took full responsibility for the Ethiopian Airlines crash.
