At least 16 flights to and from London's Heathrow Airport were cancelled on Thursday, a day after technical problems with Britain's air traffic control system caused widespread disruption across the country's airports.
National Air Traffic Services (NATS), which provides air traffic control services for planes flying in UK airspace and the eastern part of the North Atlantic, said on Wednesday its systems were fully operational with capacity returning to normal after it switched to a back-up system.
The second outage in as many years at NATS also affected Gatwick Airport near London, Edinburgh Airport in Scotland and other locations, resulting in 122 cancellations as of 1830 GMT on Wednesday, according to aviation analytics firm Cirium.
Transport minister Heidi Alexander said she would meet NATS' chief executive Martin Rolfe "to understand what happened and how we can prevent reoccurrence".
NATS is working closely with airlines and airports to clear the backlog, Alexander wrote on social media platform X.
Heathrow's website showed that at least 16 flights, including departures to Brussels and Toronto and arrivals from New York and Berlin, had been cancelled on Thursday.
The airport, Britain's largest and Europe's busiest, was also hit by a fire at a power sub-station in March which stranded thousands of passengers.
Ryanair Chief Operating Officer Neal McMahon called on NATS' Rolfe to resign, saying no lessons had been learnt since the August 2023 disruption caused by a malfunctioning in the automatic processing of flight plans.
NATS, which on Wednesday apologised to those affected by the failure, did not immediately respond to a Reuters request for a response to McMahon's comments.