NATS outage cancels more than 1,300 UK flights, with 177 more cut on Wednesday

Britain's third major air traffic failure in just over three years spilled into 9 September. Flightradar24 counted about 1,300 cancellations to or from UK airports on Tuesday and 177 more on Wednesday, nearly all of them at Heathrow. NATS, the public-private company that runs UK airspace from Swanwick near Southampton, said a fault in its flight data processing system was identified after 13:00 BST and restored at 19:34 BST. It said safety was not compromised.

Heathrow paused departures around lunchtime. Traffic restarted, then stalled again. By 17:00 BST almost no flights were leaving or arriving. Thirteen inbound aircraft diverted to other British and European fields. Gatwick, Stansted, London City, Manchester, Luton, Edinburgh, Birmingham, Bristol and Belfast all reported delays or cancellations. FlightAware recorded about 490 delayed departures and 525 cancelled or delayed arrivals at six of those airports by mid-afternoon.

Ryanair cancelled 50 flights and said more than 65,000 of its passengers were delayed. EasyJet and British Airways each cancelled more than 100 services. Cirium put Heathrow's cancelled or unworkable arrivals at 38 of 661 scheduled movements. British Airways cancelled 16 of 333 planned departures from the hub. London City lost more than 40 percent of inbound and outbound services. Eurocontrol said some aircraft bound for Britain were held on the ground at European airports because there was no slot to land.

Airlines cancelled evening flights on purpose. Crews and aircraft that leave London six hours late are out of position for the first wave on Wednesday. British Airways told passengers disruption would last into Wednesday and offered free rebooking until Friday. Heathrow said late on Tuesday that departures had resumed with restrictions and that arrivals were suspended for the rest of the night.

The wording of the NATS updates sounded familiar. In 2023 a computer at Swanwick failed when it received two conflicting flight plans, and the flight-plan processing system stopped. On 8 September NATS first said engineers had found a problem with Swanwick's "flight-processing system." Recovery took longer than the company had hoped. Ryanair called for the NATS chief executive to resign. Wizz Air asked for reforms. The Civil Aviation Authority said it would consider whether further steps were needed.

NATS provides air traffic services to 15 UK airports. The company is part owned by the government and part owned by a consortium of airlines. Each outage now follows the same public script: an assurance that safety held, an apology for the backlog, and a political argument about whether a system this central should fail three times in three years.

Passengers on 9 September are living with the lag. Aircraft and crews are in the wrong cities. Heathrow is still clearing Tuesday's queue. Anyone booked through London this week is being told to check the airline, not the airport app, before leaving home. The technical fault lasted four hours. The operational hole will last days.

The open question is not whether NATS can write another incident report. It is whether the flight data system at Swanwick can take a single bad input without closing the busiest airspace in Europe. Airlines have asked that question after each of the last three failures. They have not received an answer that changes how Wednesday morning looks on a departure board.