Software Glitch Triggered UK Flight Chaos in a Millisecond, Air Traffic Control Says

A previously unknown software defect in the UK's air traffic control system corrupted flight data in a single millisecond, causing a six-hour outage and mass cancellations, National Air Traffic Services has said.

The error struck at 10am and engineers were notified at 10.02am that the link between the National Airspace System and London area control had dropped. By 10.06am it appeared to have recovered with no operational impact, but investigations continued. At 12.32pm the link dropped again and a major incident was declared. The system failed completely at 1.32pm, and full operations only resumed at 7.30pm.

The report said the fault occurred when a manual request for an aircraft code was paused for a higher priority activity and did not resume correctly. Nats chief executive Martin Rolfe confirmed it was a software issue, not incorrect actions by military or civil operators, and said mitigation was in place while a permanent fix is tested.

More than 2,000 flights were cancelled and hundreds of thousands of passengers disrupted after the 8 September failure. Transport secretary Heidi Alexander called the disruption completely unacceptable and tasked the Civil Aviation Authority with an independent review, to be published within six months. Airlines are demanding compensation, with Ryanair calling for Rolfe's resignation.