A long weekend in Britain—the last one before summer draws to a close—could have been idyllic. But for many, it became a nightmare as flights were canceled or delayed indefinitely due to a technical glitch.
Scores of flights departing from and arriving in London on Monday, a U.K. holiday, were disrupted after a technical issue affected the National Air Traffic Services’ (NATS) ability to automatically process flight plans on its systems.
London Heathrow, which is among the world’s busiest airports, saw 331 flight delays and 49 cancellations by 4:30 p.m. local time on Tuesday, according to data from Flightradar24.
Meanwhile, the capital city’s Gatwick airport saw 26 cancellations and 251 delays—meaning more than half of all flights out of Gatwick departed late.
The disruption wasn’t limited to London, however. Airports in major hubs Manchester, Birmingham, and Glasgow were still also experiencing swaths of delays on Tuesday, the data showed.
What caused the chaos?
On Monday afternoon, NATS confirmed a fault that forced it to enter flight plans manually, preventing it from operating quickly and managing flight volumes like it usually does.
The issue was resolved in just a few hours, but the backlog caused 27% of all U.K. departures and arrivals to be canceled on Monday, aviation analytics firm Cirium told Fortune.
U.K. transport minister Mark Harper said on Tuesday that it would still take some time for the problems caused by the technical meltdown to be fully resolved.
“I accept it’s disrupted thousands of people and it is going to take some days to get people back to where they should be,” he told the BBC, adding that the U.K.’s Civil Aviation Authority would investigate what caused the technical issues. He ruled out the possibility of a cyberattack.
'It was a technical issue.. it was not a cyber security incident'
— BBC Breakfast (@BBCBreakfast) August 29, 2023
Transport Secretary Mark Harper spoke to #BBCBreakfast about the disruption to air travel in and out of the UKhttps://t.co/0wyScnzTp7pic.twitter.com/reJh9zloV0
The issue, although quickly resolved, was exacerbated since it was one of Britain’s busiest days for travel, with people returning from summer vacations and quick getaways over the three-day weekend.
“It will take some time for flights to return to normal, and we will continue to work with the airlines and the airports to recover the situation,” NATS operations director Juliet Kennedy said in a statement. The organization has not yet provided a clear cause for the glitch.
While this type of disruption is rare, it isn’t unheard-of.
In 2014, a number of European flights faced disruptions following a technical problem on NATS’s air traffic control system, and in 2019, a radar display glitch led to many flight cancellations.
The chaos that ensued in airports resembled last summer, when passengers were left stranded in Britishairports for hours at a time. It was the first summer following COVID-19 lockdowns, when high demand was met with a staffing shortage that meant many airports across Europe couldn’t manage.
This year, the volume of flights departing the U.K. over the long weekend was scheduled to be 10% higher than the same time last year, according to the New York Times—that’s 83% higher than in 2021.
What are airlines doing?
Amid high demand to travel in and out of Britain, major airline carriers have warned stranded passengers to brace for further delays. British Airways is offering customers free flight changes for any other date, subject to availability.
“Like other airlines operating in the U.K., we are continuing to experience the knock-on effects of yesterday’s NATS Air Traffic Control issue, which includes unavoidable delays and cancellations,” a British Airways spokesperson told Fortune in a statement, adding that passengers should check the status of their flights before making their way to the airport.
Meanwhile, Dublin-based Ryanair said it had to cancel 250 flights on Monday, impacting about 40,000 travelers. Further cancellations followed on Tuesday, but the company expects operations to return to normal on Wednesday with 3,200 scheduled flights.
Michael O'Leary, CEO of the Ryanair Group gives an update on delays/cancellations due to UK ATC failure on Aug 28 pic.twitter.com/HoebuSNqBy
— Ryanair (@Ryanair) August 29, 2023
“It is sadly outside of our control,” Ryanair chief Michael O’Leary said in a video statement Tuesday. “We have been in contact with U.K. NATS. We still haven’t had an explanation from them—what exactly caused this failure yesterday? And where were their backup systems? It’s not acceptable.”
Other carriers like low-cost airline EasyJet were also forced to ground flights. The airline said it was working with authorities to “understand the impact of this issue,” and offered affected passengers refunds on their flights.
While airlines are doing their bit in trying to help passengers find alternatives, it could be a while before airports bounce back to their regular operations. Heathrow and Gatwick airports have told travelers to check with airlines if their flight is still flying as scheduled.
Due to yesterday’s technical issues suffered by UK Air Traffic Control, there may be some continuing disruption on some routes, including flight cancellations. (1/2)
— Heathrow Airport (@HeathrowAirport) August 29, 2023