Heathrow Airport was struggling to return to normal on Wednesday, 9 September, after a major failure in Britain’s air traffic control system forced it to halt arrivals overnight and contributed to the cancellation of more than 1,750 flights across the UK.

Flights are operating again at Heathrow, but the airport warned that disruption would continue as airlines reposition aircraft and crews left in the wrong places by Tuesday’s shutdown. It told passengers to check directly with their airline and travel to the airport only if their flight had been confirmed.

The disruption began Tuesday afternoon when National Air Traffic Services, or NATS, suffered a failure in its flight processing system. The problem sharply reduced the number of aircraft that could be handled and disrupted operations at Heathrow, Gatwick, Stansted, Manchester, Birmingham and other airports.

NATS said the technical problem had been resolved, but the interruption created a backlog that spread across Britain and into the wider European aviation network. The company provides air traffic control services to 15 UK airports.

Heathrow initially resumed departures Tuesday but suspended arrivals for the remainder of the night as the system recovered. On Wednesday, it said operations were recovering but warned of further cancellations and delays.

“Flights are operating today, however some knock-on disruption is expected as airlines reposition aircraft and crew,” Heathrow said.

More than 1,750 flights cancelled

The Associated Press reported that more than 1,750 flights had been cancelled as airlines struggled with the aftermath of the outage. Flight-tracking data cited separately by British media showed about 1,300 flights to and from UK airports were cancelled on Tuesday, with another 177 already cancelled Wednesday morning, almost all of them at Heathrow.

Reuters earlier put Tuesday’s cancellations at more than 1,000 and said hundreds of thousands of passengers had been stranded or otherwise affected.

British Airways, whose main hub is Heathrow, cancelled or diverted about 100 flights and said tens of thousands of its passengers were affected. The airline said Wednesday that the underlying air traffic control problem had been fixed but warned that aircraft and crews remained displaced across its network.

Ryanair said around 150,000 of its passengers were affected Tuesday and more than 200 flights were cancelled, according to Reuters. EasyJet also warned that the UK failure had caused disruption across Europe.

India-UK flights caught in disruption

The breakdown also hit services between India and Britain. Air India, IndiGo and British Airways flights linking India with the UK were among those affected by delays, diversions and cancellations. Air India flight AI 2107 from Delhi to London Heathrow was diverted to Paris after the disruption prevented it from completing its scheduled journey to London.

IndiGo services were also affected. Flight tracking showed its Mumbai-Heathrow service 6E1 scheduled for Wednesday as cancelled, while a Heathrow-Delhi service had been cancelled during Tuesday’s disruption. Passengers travelling between India and Britain were advised to check directly with airlines because schedules remained subject to change.

The impact on long-haul flights illustrates why an air traffic control outage lasting only a few hours can take considerably longer to unwind. An aircraft diverted to another airport may no longer be available for its next scheduled service, while pilots and cabin crew can run into legally mandated limits on working hours.

That produces a cascade of cancellations well after the original technical problem has been repaired.

Failure traced to flight processing system

NATS said it had identified the problem in its flight processing system, which handles information required by controllers to manage aircraft moving through UK airspace. The failure began at about 1 pm local time Tuesday and the system was fixed several hours later. NATS said the subsequent recovery was complex because of the scale of the backlog.

NATS Chief Executive Martin Rolfe said a cyberattack had been ruled out. “We have, at this point, ruled out cyber,” Rolfe told the BBC. He said the latest failure appeared to be different from previous incidents.

The company has not yet publicly established the underlying technical cause of the failure beyond identifying the affected flight processing system.

The outage has become a political issue because it is the latest in a series of failures affecting Britain’s air traffic control infrastructure. UK Transport Secretary Heidi Alexander summoned Rolfe to explain what had happened and what NATS would do to prevent another breakdown.

“I am seeking assurances that lessons will be learned and systems that support aviation are up to the job,” Alexander said.

Airlines have responded more aggressively.

Ryanair renewed its demand that Rolfe resign, while Wizz Air also questioned whether he should remain in the job. Ryanair Chief Operating Officer Neal McMahon said the scale and recurrence of UK failures compared poorly with disruptions in other countries.

Ryanair also criticized NATS for paying £175 million in dividends to shareholders last year, arguing that more money should have gone into technology and staffing.

NATS is neither a conventional government department nor an entirely private company. It operates as a public-private partnership whose owners include the UK government, airlines including British Airways and easyJet, and institutional investors.

Third major disruption in three years

The latest failure has revived questions about the resilience of Britain’s air traffic control systems because it follows two other significant disruptions.

In August 2023, an unusual flight plan triggered a failure in NATS’ automatic flight-plan processing system. The disruption occurred during one of the busiest travel periods of the year and ultimately cost airlines more than £100 million in refunds, compensation and other expenses.

Another technical failure in July 2025 affected radar systems and disrupted operations for several hours at Heathrow and other airports.

NATS has since invested in upgrading and replacing parts of its ageing infrastructure. Its financial disclosures have described work on the National Airspace System flight data processor and plans for a replacement system intended to improve resilience while a newer platform is developed.

Tuesday’s breakdown will therefore intensify scrutiny over whether those improvements have proceeded quickly enough.

Heathrow disruption could take time to clear

Heathrow is particularly vulnerable to knock-on disruption because the airport normally operates close to its available runway capacity. Large numbers of cancellations can leave aircraft, crews and passengers scattered across multiple airports, while scheduled flights continue arriving into the system.

British Airways said Wednesday that some flights would remain affected because aircraft and employees were out of position. Heathrow also deployed additional staff in its terminals as passengers tried to rebook journeys.

Gatwick, Stansted and Luton were operating again Wednesday as well, although each advised travelers to check their flight before leaving for the airport.

For passengers whose flights are cancelled, UK rules generally require airlines to offer either a refund or alternative transportation. Airlines must also provide care such as food and, where necessary, accommodation during qualifying delays. Cash compensation may not apply when the disruption results from circumstances outside an airline’s control, such as an independent air traffic control failure.