NATS flight-processing fault grounds hundreds of UK departures

National Air Traffic Services said on 8 September that a fault in its flight processing system had disrupted departures across the United Kingdom. The first public note went out at 13.46 BST. At 15.25 NATS named the system. At 16.40 it said a fix was in and that the system was starting to recover. Passengers were told to check with airlines. Airspace stayed open. Take-offs did not.

FlightRadar24's count moved through the afternoon from about 200 cancellations to at least 425 flights in or out of the UK. EasyJet and British Airways each cancelled more than 100 services in some tallies. FlightAware, at 15.18 GMT, showed about 490 delayed departures at Heathrow, Gatwick, London City, Luton, Edinburgh and Bristol, and 525 arrivals at those six airports cancelled or delayed. Cirium said 38 of 661 scheduled Heathrow arrivals had been cancelled or could not operate. British Airways cancelled 16 of 333 scheduled Heathrow departures.

Heathrow paused departures around lunchtime, restarted, then stopped again. By 17.00 BST, BBC reporting said almost nothing was leaving or arriving. Thirteen Heathrow-bound flights diverted to other airports in Britain and Europe. Gatwick, Manchester, Stansted, London City and East Midlands all reported the same constraint. Because aircraft ended the day in the wrong cities, the backlog will last into Wednesday even if the software holds.

Ryanair said more than 65,000 of its passengers faced delays of up to eight hours and that it had cancelled more than 50 flights. It called on NATS chief executive Martin Rolfe to resign. Wizz Air asked for reforms. The Civil Aviation Authority said it would consider whether further steps were needed. Transport Secretary Heidi Alexander wrote that technicians had identified the issue and were fixing it, and told passengers to check with their airline.

This is the third major NATS failure in a little over three years. Airlines have used that sentence in every statement today. The agency is a public-private monopoly for en-route traffic in UK airspace. When its flight processing system fails, no individual airport can clear its own queue. Controllers can still separate aircraft that are already airborne. They cannot file and release a normal departure stream.

NATS has not published a technical post-mortem. The public record on 8 September is three timestamps, one named subsystem, one claimed fix, and a set of airline and tracker counts that do not match each other because they sample different hours. The durable fact is operational: a software fault at the national provider, not weather and not a strike, emptied departure boards at the country's main hubs on a weekday in September.

Passengers still in terminals after 17.00 were living with the second-order problem. Crews go out of hours. Aircraft night-stop in the wrong hangar. Connecting banks at Heathrow and Gatwick collapse. A four-hour outage becomes a 24-hour recovery. That is why Ryanair's attack on Rolfe arrived before the system had even finished coming back. The political argument about NATS resilience will run longer than the fault itself.