UK Flight Chaos: Millisecond Software Glitch Behind Disruption to Thousands of Flights

Britain’s National Air Traffic Services (NATS) has identified a software defect as the cause of the major disruption to air traffic on September 8. According to its preliminary investigation, the problem occurred in a small section of the National Airspace System (NAS), which supports the management of UK airspace. The software assigns identification codes to aircraft, which are used to identify flights on radar. A processing error lasting just a millisecond caused an aircraft-code request to resume incorrectly, resulting in corrupted data and affecting subsequent flight-data updates. NATS said the incident was not related to the major 2023 system outage or military intervention.

With controllers having reduced access to some flight information, NATS imposed restrictions on air traffic to maintain safety. Although the technical problem was limited to flights managed by the London Area Control Centre, restrictions were applied across the UK while the system was restarted and flight data was reloaded. The restrictions lasted around six hours, and while operations returned to normal the same evening, it took more than two days to clear the resulting passenger disruption. NATS said the software problem has been identified, mitigation measures are in place and a permanent fix is being safety-tested and deployed.