Two Ethiopian Airlines pilots reportedly fell asleep and missed their landing during a flight on Monday (Aug. 15), according to a report by commercial aviation news site Aviation Herald.

The pilots were operating a Boeing 737-800 from Khartoum, the capital of Sudan, to Addis Ababa, the capital of Ethiopia “when the pilots fell asleep” and “the aircraft continued past the top of descent,” according to the report.

The pilots reportedly fell asleep at 37,000 feet and were unable to be reached by air traffic control. They were woken by an onboard alarm that began blaring when the plane passed the point of descent and the autopilot disconnected. After about 30 minutes, the “disconnect wailer woke the crew up, who then maneuvered the aircraft for a safe landing on runway,” according to the news site.

Ethiopian Airlines did not confirm that the pilots fell asleep, but in a statement today (Aug. 20), the company said the crew members involved had been suspended pending a further investigation. “Appropriate corrective action will be taken based on the outcome of the investigation,” the airline said.

It was not immediately clear how many passengers were on board but the Boeing 737-800 has a capacity of up to 189 passengers depending on the layout. Ethiopian Airlines is Africa’s largest airline with an operating fleet of 138 planes that fly to almost 130 destinations in Africa and around the world.

Aviation analyst Alex Macheras expressed on Twitter his shock at the “deeply concerning incident,” which he says may have been the result of pilot exhaustion. “Pilot fatigue is nothing new, and continues to pose one of the most significant threats to air safety — internationally,” he tweeted on Thursday (Aug. 18).

”Just last week, pilots publicly criticised UK leisure airline Jet2 for ‘refusing to recognise concerns about pilot fatigue,’” he added.