Nats says a software defect that corrupted data "in the space of a millisecond" caused an air traffic control outage on 8 September, leading to more than 2,000 cancelled flights and widespread disruption. The fault began at 10:00, its severity became clear about 2.5 hours later, restart began after 15:15 and restrictions were lifted at 19:30. Transport Secretary Heidi Alexander called the event "completely unacceptable"; the Civil Aviation Authority has opened a review and Airlines UK is demanding compensation and a resilience plan.
Millisecond Software Defect at Nats Triggered Widespread UK Flight Chaos
Thousands of passengers were delayed by the NATS outage [Getty Images]
Britain's national air traffic service, Nats, has concluded that a software defect that corrupted system data "in the space of a millisecond" caused an air traffic control outage on 8 September, triggering widespread disruption across UK airspace.
What Happened
Nats says the fault produced corrupted data that reduced the information available to air traffic controllers. To preserve safety, controllers imposed temporary traffic restrictions, which led to cascading delays and cancellations affecting flights at major airports including Heathrow, Gatwick, Luton and Glasgow.
Timeline
- 10:00, 8 September — The software defect occurred.
- ~12:30 — The full severity of the problem became apparent (around two and a half hours later).
- Just after 15:15 — System restart began.
- 19:30 — Restrictions on UK airspace were lifted, though disruption took days to unwind as aircraft and crews were out of position.
Impact
The outage resulted in more than 2,000 cancelled flights and affected hundreds of thousands of passengers. Many travellers faced long delays, overnight stays in airports and unexpected costs. The operational knock-on meant it took several days to return schedules to normal.
Addie Kitson was hit with almost £100 in unexpected costs when her flight back from China was diverted to Stockholm [Addie Kitson]
Responses
"You can fly to almost anywhere from almost any airport at almost any time. If that stops, even for a moment, then you get huge disruption." — Martin Rolfe, Nats CEO
Rolfe apologised and said he would not resign, describing the defect as "very, very obscure" and emphasising that safety was never in question. Transport Secretary Heidi Alexander called the disruption "completely unacceptable" and said the Civil Aviation Authority has launched a review. Airlines UK is demanding immediate compensation from Nats and a credible resilience plan.
Context and Passenger Experience
This is the third significant national air traffic incident in three years: a major computer shutdown in 2023 disrupted roughly 700,000 passengers, and a smaller outage in 2025 caused around 150 cancellations. Passengers reported poor support from some carriers; one traveller, Addie Kitson, said her flight from China was diverted to Stockholm, leaving her stranded in the airport for 19 hours and out of pocket by nearly £100 despite receiving only an £11 food voucher.
Next Steps
The CAA review will examine why the defect was not detected earlier and what steps are needed to improve resilience. Airlines and consumer groups are seeking clarity on compensation and assurances that Nats will fix vulnerabilities to prevent future national-scale outages.
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