A software defect in the United Kingdom’s air traffic control system caused widespread flight cancellations and delays on September 8, disrupting the travel plans of approximately 330,000 passengers. The National Air Traffic Services (NATS) identified the issue as a millisecond-long software glitch within the system responsible for allocating identification codes to aircraft, a critical process for tracking flights on radar.
According to NATS, the problem occurred when a request to assign an aircraft identification code was temporarily paused to handle a higher-priority task. Due to a previously unknown defect in legacy software, the system failed to resume processing correctly, resulting in corrupted flight data. This failure unfolded in the span of a millisecond and triggered backup manual handovers and reduced operational capacity. The glitch led to extensive delays, more than 2,000 flight cancellations, and a disruption backlog that took over two days to clear.
The initial error was detected around 10 a.m., with engineers temporarily resolving the malfunction. However, the issue recurred at approximately 12:30 p.m., prompting NATS to declare a major incident. Flight disruptions persisted throughout the day and continued into the following night, affecting flights across the UK and international routes.
Transport Secretary Heidi Alexander described the disruption as “completely unacceptable” and called for a comprehensive review by the Civil Aviation Authority (CAA) into NATS’s handling of the incident. She expressed concern over why the defect was not identified and rectified before causing such significant chaos. The government also indicated the review would assess whether NATS remains fit to fulfill its responsibilities. Despite calls from airlines, including Ryanair, demanding the resignation of NATS Chief Executive Martin Rolfe, Alexander stated she would not remove him at this point.
Rolfe acknowledged the incident was linked to software rather than operator error and apologized for the widespread inconvenience. He emphasized that safety was never compromised during the outage. Officials noted this was the third major air traffic control failure in the UK since summer 2023, following comparable disruptions in July 2025 and August 2023. Although Rolfe indicated the current event was unrelated to previous failures, airlines have urged for an overhaul of NATS’s systems and leadership to prevent future occurrences.
The incident has renewed scrutiny over the resilience of the UK’s air traffic management infrastructure, as stakeholders seek assurances that lessons will be learned and corrective measures implemented to minimize the risk of similar failures going forward.