(NewsNation) — Two pilots on an Ethiopian Airlines Boeing plane fell asleep and missed their landing Monday, according to media reports.

The Aviation Herald said the pilots were flying from Khartoum, Sudan to Addis Ababa, Ethiopia, when they started to go to sleep.

The New York Post reported that the plane was supposed to touch down in Addis Ababa at 6:20 a.m., but air traffic control in Ethiopia’s capital noticed that instead of descending at that time, the jet instead remained at a cruising altitude of 37,000 feet.

When controllers tried to contact the pilots, they had no luck, the Aviation Herald said, but then, the autopilot disconnected, setting off an alarm that woke the crew up, and allowed them to maneuver a safe landing.

After remaining on the ground for 2.5 hours, the aircraft departed for its next flight.

Eventually, the two woke up, and landed the plane on its second approach, per the BBC. One aviation analyst, Alex Macheras, called the incident “deeply concerning” on Twitter, blaming it on “pilot fatigue.”

“Pilot fatigue is nothing new, and continues to pose one of the most significant threats to air safety internationally,” he said.

Ethiopian state-run news outlet Fana said Ethiopian Airlines put the pilots on leave.