Hundreds of Flights Into Britain Canceled After ‘Technical Issue’ With U.K. Air Traffic Control

Airlines were forced to cancel hundreds of flights and delay hundreds more on Monday after Britain’s air traffic control service experienced a “technical issue” that caused widespread disruption on one of the country’s busiest travel days of the year.

More than 200 flights departing from Britain were canceled, according to Cirium, the aviation analytics company, along with 271 that were scheduled to arrive in the country on Monday. Many other flights would be delayed by more than eight hours, “which will inevitably result in a cancellation,” Cirium added.

NATS, Britain’s National Air Traffic Service, said a technical problem had affected its ability to automatically process flight plans, which meant that the information had to be entered manually, slowing down the process.

While British airspace was not closed at any time, NATS restricted the number of flights departing from and landing at airports in order to maintain safety while its engineers tried to fix the problem. At about 3 p.m. local time, NATS said it had resolved the issue, but noted that air traffic remained disrupted. Britain’s government has a 49 percent stake in NATS, which is a public-private partnership.

The delays hit during a particularly heavy travel period, as people returned from summer vacations or extended weekend trips on Monday’s “bank holiday,” or national day off, in Britain.

Thousands of holidaymakers spent hours stuck in departure lounges or on runway tarmac, facing long delays and uncertain departure times.

In Palma de Mallorca, Jon Hughes, 49, boarded a plane bound for the English city of Leeds at about 1 p.m. local time with his two children, ages 13 and 15. Once seated, he said, they were told that the plane had been allotted a departure slot in about seven hours.

“It’s very hot and kids are getting restless,” he said in a message. “We don’t know how long we will be stuck on the plane. Or even if we will get home today.”

Two hours after NATS said it had resolved the technical issue, Mark Harper, the government minister responsible for transport policy, said flights were still affected, and advised travelers to “be aware” of their rights when flights were delayed or canceled.

Heathrow Airport, near London, advised passengers to contact their airline before heading there, and Edinburgh Airport told passengers not to leave home before checking the status of their flight.

Jamie Steele, 39, a British nurse returning to Manchester from a vacation in the Italian city of Pisa, had been set to depart at 10.30 a.m. local time. Four hours later, he was still sitting in the plane on the tarmac. The pilot told passengers that the plane would have a departure slot in the next three hours, but added that he was “not sure he trusts the time given.”

“It’s difficult not knowing the time we will get home,” Mr. Steele said in a message.

Louise Haigh, the lawmaker in charge of transportation policy for the opposition Labour Party, described the disruption as “extremely concerning for passengers” on “one of the busiest days of the year.”

The number of flight departures during the three-day holiday weekend had been scheduled to be 10 percent higher than the same period the year before, according to Cirium, and 83 percent higher than in 2021, when the Covid-19 pandemic drastically reduced air travel.

Alex Macheras, an aviation analyst, said the backlog of flights would cause flight disruptions for several days.

“That’s probably the worst timing ever given it’s the end of August, which is typically one of the busiest weeks of the calendar year,” he said.

Mr. Macheras said that compared with last summer, when there were numerous cancellations and delays, this summer’s air travel in Britain and continental Europe had been “smooth sailing” until Monday.

The disruption is expected to have little effect on overall operations for U.S. airlines, which collectively had just over 140 planned flights to or from Britain on Monday.

European flights were disrupted for hours in December 2014 because of a technical problem at NATS’s air traffic control center in Swanwick, England.

Niraj Chokshi contributed reporting.