Hundreds of departing flights from major British airports were disrupted on Tuesday after air-traffic control provider NATS experienced a technical issue.
Heathrow, Gatwick, Manchester and Stansted were among the airports affected by cancellations and delays.
NATS said it had implemented a fix and the flight system was starting to recover. However, the knock-on effect was expected to last for several hours.
“Our engineers are on-site and working urgently to resume normal operations as quickly as possible,” it said initially. “Flights are still departing and airspace is open, but recovery will take some time.”
UK Transport Secretary Heidi Alexander acknowledged the issue would be frustrating for passenger and apologised.
Flight tracking website Flightradar24 said on social media that arrivals and departures were being regulated at airports in the London flight information region.
About 100 flights were cancelled at Heathrow and 367 delayed, according to data on platform FlightAware. About 250 flights were delayed at Gatwick, almost a third of the total, data showed.
Edinburgh Airport said in a post on X that the issue might affect its operations. Ireland's Dublin Airport said flights leaving and arriving were also being disrupted.
Other airports reporting delays or cancellations included London's Luton and Birmingham, as well as Aberdeen and Glasgow.
British Airways said it was experiencing disruption to flights because of the issue. “This is entirely out of our control and we're in touch with our customers whilst our teams work to get them on their way as quickly as possible,” a statement said.
easyJet said the issue was causing delays across Europe. Ryanair, Wizz Air and Virgin Atlantic were not immediately available for comment.
Tuesday's delays follow previous incidents that caused severe disruption.
In 2024, Britain's aviation regulator said NATS needed to review its contingency plans after the automatic processing of flight plans had malfunctioned a year earlier, causing chaos across Britain's airports.
Airline bosses said it had cost them more than £100 million ($135.5 million) in refunds and compensation.
In July last year, a radar-related technical issue in Britain's air-traffic control system disrupted flights for more than four hours at major airports in London and elsewhere, including Heathrow.
