NATS air traffic control fault cancels hundreds of UK flights and diverts Heathrow traffic

What happened

Hundreds of flights were cancelled at airports across the United Kingdom on 8 September after air traffic control provider NATS hit a technical fault in its systems. According to the BBC's live coverage of the incident, the failure grounded departures for much of the afternoon, with recovery only beginning in the early evening.

NATS said in a post on X that the underlying system issue had been resolved and that it was operating normally again, but that clearing the backlog of flights was taking "longer than we had hoped". The company apologised and told passengers to keep checking with their airlines.

Diverted jets and a saturated Heathrow

The disruption rippled out across UK and European airspace. The BBC counted at least 22 flights that were due to land at Heathrow but were diverted, to Stansted, Gatwick, Manchester, Birmingham, Luton and Glasgow within the UK, and to Paris, Brussels, Amsterdam and Frankfurt further afield.

Heathrow itself effectively filled up. BBC transport correspondent Katy Austin reported that the airport reached a point where it could not accept any more arriving aircraft because nothing was departing, and the skies above the airport went quiet as the backlog built.

Before full service resumed, an airport source told the BBC that NATS was releasing small numbers of aircraft as "trials" at various airports, with a view to ramping up towards regular operations.

Airlines count the cost

British Airways said the fault forced it to cancel or divert more than 100 flights, inconveniencing tens of thousands of customers. Although NATS told the airline the fault had been fixed, BA warned of a "significant knock-on impact", since its aircraft and crews had ended up out of position.

The airline asked passengers whose flights had been cancelled not to travel to the airport, said its call centres were extremely busy, and offered customers due to fly on the day or the following day the option to change bookings through its website.

Passengers left waiting

The human effects were visible across the network. A passenger named Emma Chun told the BBC she was still on board her cancelled New York-bound flight at Heathrow more than five hours after its scheduled departure time, because no steps were available to let people off; cabin crew served the starters while she waited. She had been rebooked via Copenhagen for the following day.

At Gatwick, a passenger flying to Italy for her own wedding described chaotic scenes, with people queuing at empty airline desks and calling carriers to find alternative flights. In Malta, UK-bound departures were cancelled outright, with British Airways telling travellers that accommodation arrangements were being worked on.

A repeat failure, and political pressure

The incident drew immediate political criticism because it is not the first. Shadow transport minister Greg Smith pointed out that a major outage linked to a fault at NATS's Swanwick centre had already brought UK airports to a standstill last year, and that Transport Secretary Heidi Alexander had promised afterwards to work with NATS to prevent a recurrence. Alexander said she was aware of the technical issue and apologised for the frustration.

Notably, neither NATS nor the government has publicly described what the fault actually was, how far it propagated, or why the recovery proved slower than expected.

Why it matters

Air traffic control is safety-critical national infrastructure running on complex, long-lived software, and the UK concentrates airspace management in a single provider. That makes NATS a single point of failure for the country's aviation network: one technical fault can ground departures nationwide, saturate the busiest airport in the country, and push diverted aircraft across two continents within hours.

This is also the second major NATS outage in two years, which turns the story from bad luck into a resilience question. The visible failure lasted hours, but the real cost will be measured in days as airlines reposition planes and crews and rebook tens of thousands of passengers. For anyone building or operating critical systems, it is a reminder that redundancy, graceful degradation and rehearsed recovery matter as much as fixing the bug itself — and until NATS explains the cause, the industry cannot judge whether this failure mode was preventable.