NATS has traced the 8 September shutdown of UK air traffic control to a software defect in its flight data system, ruling out human error in the incident that disrupted flights across the country. The outage affected hundreds of thousands of passengers and led to more than 2,000 cancellations, with departures and arrivals hit by delays and manual operating procedures.
The fault was found in a small section of code within the National Airspace System, which manages UK airspace and allocates aircraft identification codes used on radar. NATS said the problem emerged during a narrow processing window when a manual request for a squawk code was interrupted by a higher-priority task and then resumed incorrectly, corrupting output data.
Restrictions were imposed across the UK to keep traffic safe while the system was restarted and flight data reloaded, reducing capacity and creating a backlog that took more than two days to clear. NATS is already using mitigation measures while a permanent fix undergoes safety testing before deployment.