NATS Blames Millisecond Software Defect for Mass UK Flight Cancellations

A preliminary report has attributed the widespread flight disruption across the United Kingdom earlier this month to a software defect that unfolded in a fraction of a second, clearing human operators of blame for the chaos.

NATS, the company that runs the country's air traffic control system, said the fault occurred on Sept. 8 in the National Airspace System, the component that assigns codes allowing controllers to identify flights on radar. The problem triggered the cancellation of more than 2,000 flights into and out of the UK, affecting hundreds of thousands of travellers.

"This happened in the space of a millisecond," the report said, describing a defect confined to a small subsection of coding within a specific part of the flight data system.

The disruption left passengers stranded for hours in terminals and on airport runways, and it took days for schedules to return to normal. It was the latest in a series of setbacks for NATS and intensified calls for its chief executive, Martin Rolfe, to step down.

Rolfe apologised again for the upheaval and said the incident did not stem from "any incorrect actions by either military or civil operators." He added that mitigation measures are in place while a permanent fix is tested and deployed, and that the event was unconnected to an earlier outage in 2023 or a radar issue in July last year.

Transport Secretary Heidi Alexander met Rolfe after the disruption and instructed the organisation to carry out a full investigation. She said she had now received the report and, while she was pleased that passenger safety had been protected, it was clear there was an urgent need to understand why the issue was not found and resolved before it caused chaos.

Alexander has asked the Civil Aviation Authority to conduct an independent review to verify NATS' findings and to examine the company's investment plans for improving resilience, along with its regulatory accountability.

The UK government holds a 49% stake in NATS, making it the largest shareholder with a veto over key decisions. Airlines, airports, investors and employees own the remaining shares in the public-private partnership.