National Air Traffic Services says a software defect corrupted flight data 'in the space of a millisecond', causing a six-hour outage that led to more than 2,000 flight cancellations. UK ministers say the report leaves key questions unanswered.
Key facts
- A software defect corrupted flight data in the UK's air traffic control system, according to National Air Traffic Services.
- The fault occurred 'in the space of a millisecond', per the report.
- The failure caused a six-hour outage.
- More than 2,000 flights were cancelled and hundreds of thousands of passengers were affected.
- UK ministers say the report leaves unanswered questions about why the issue was not found and fixed earlier.
A software defect in part of the UK’s air traffic control system corrupted flight data “in the space of a millisecond”, leading to a six-hour outage and mass airline cancellations and delays across the UK last week, National Air Traffic Services (Nats) has said.
The failure led to more than 2,000 flights being cancelled and affected hundreds of thousands of passengers, according to the BBC and the Guardian, which both reported on the findings.
According to the Guardian, the incident report attributes the disruption to the software defect that corrupted flight data almost instantaneously, before cascading into a lengthy outage that grounded a significant number of flights.
UK ministers responded to the report by saying it still left questions unanswered. They said they needed “to urgently understand why this issue was not discovered and fixed before it caused chaos”, according to the Guardian.
The scale of the disruption underlines how a single, momentary technical fault within critical aviation infrastructure can ripple out to affect large numbers of travellers and airlines across the country.
Both the BBC and the Guardian reported the same headline figures of more than 2,000 cancelled flights and hundreds of thousands of affected passengers, with coverage published on 18 September 2026.
Why it matters
Air travel depends on complex software systems, and this incident shows how a fault lasting only a millisecond can cascade into hours of disruption for hundreds of thousands of people. Ministers' concerns about why the defect was not caught earlier point to wider questions about oversight and resilience in critical national infrastructure.
Frequently asked questions
What caused the UK flight chaos?
According to National Air Traffic Services, a software defect in part of the UK's air traffic control system corrupted flight data 'in the space of a millisecond', leading to a six-hour outage.
How many flights and passengers were affected?
More than 2,000 flights were cancelled and hundreds of thousands of passengers were affected, according to the BBC and the Guardian.
What have UK ministers said about the report?
Ministers said the report left questions unanswered, stating they needed to urgently understand why the issue was not discovered and fixed before it caused chaos, according to the Guardian.