UK Air Traffic Control Outage Caused by Software Defect, Says NATS

British air traffic control operator NATS has said that an outage which disrupted travel for hundreds of thousands of passengers last week was caused by a software defect.

The incident triggered 2,000 flight cancellations and days of disruption, costing airlines millions of pounds as they worked to reposition crews and aircraft and refund passengers.

NATS chief executive Martin Rolfe said the shutdown was unrelated to a separate problem in 2023 that also caused widespread disruption, and was not linked to military intervention, contrary to some media reports last week. He added that safety was not compromised at any point during the incident.

"This was a software issue in a specific part of our flight data system, that we have traced to a small subsection of coding," he said. "The issue has been identified and mitigation is in place while a permanent fix is safety tested and deployed."

Transport minister Heidi Alexander, who had demanded a report from NATS and ordered an independent review by the Civil Aviation Authority, described the disruption as "completely unacceptable".

"We need to urgently understand why this issue was not discovered and fixed before it caused chaos," she said in a statement. "It is crucial that our national infrastructure is fit for the future."

The latest incident follows a shutdown in August 2023 that caused travel chaos and cost airlines £100 million ($136 million). A smaller technical issue involving NATS in July 2025 also led to 150 cancellations. Ryanair, Europe's largest airline, has repeatedly called for Rolfe to resign since the 2023 failure.

The NATS report on the latest incident was triggered by a request for an identification code from an aircraft being followed by a request for a higher-priority activity, which paused the first request.

"Had the higher-priority request arrived even one millisecond earlier or later, the update would have completed normally," the report said.