UK air traffic control outage caused by millisecond software defect

A software defect in the UK's air traffic control system caused the cancellation of more than 2,000 flights and disrupted hundreds of thousands of passengers on September 8, according to a preliminary report released by National Air Traffic Services (NATS). The incident, which triggered a six-hour outage and a multi-day passenger backlog, has prompted an independent government review and renewed calls for leadership changes at the air navigation service provider. The report, published on September 18, attributes the failure to a previously unknown coding error within the National Airspace System (NAS). The defect occurred in the space of a millisecond when a manual request for an aircraft identification code was interrupted by a higher-priority activity. When processing resumed, the software did not restart correctly, corrupting flight data for some aircraft. NATS CEO Martin Rolfe stated the incident was not caused by incorrect actions by military or civil operators and was unrelated to previous NATS outages in 2023 and 2025. "This was a software issue in a specific part of our flight data system, that we have traced to a small subsection of coding," Rolfe said.