UK air traffic controller blames a millisecond-software glitch for flight cancellations

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LONDON (AP) — A preliminary report Friday blamed a millisecond-software defect for the cancellation of over 2,000 flights in and out of the United Kingdom last week.

NATS, formerly known as National Air Traffic Services, said Friday that the glitch on Sept. 8 was behind the mayhem at British airports and beyond, rather than any human failings — as many had speculated at the time.

It said a software defect in the National Airspace System, which allocates codes so air traffic controllers can identify flights on radar, was behind the decision to ax the flights. The move impacted hundreds of thousands of travelers.

“This happened in the space of a millisecond,” the report said.

The chaos, which stranded passengers for hours on airport runways and in terminals and took days to clear up, was the latest embarrassment to afflict NATS, which operates the U.K. air traffic control system. It prompted mounting calls for its chief executive Martin Rolfe to stand down.

"This was a software issue in a specific part of our flight data system, that we have traced to a small subsection of coding,” he said, adding that mitigation measures are in place while a permanent fix is tested and deployed.

Apologizing once again for the chaos, Rolfe said it was not a result of "any incorrect actions by either military or civil operators.”

Rolfe also said the latest incident was not connected to a previous outage in 2023 or a radar issue in July last year.

U.K. Transport Secretary Heidi Alexander met with Rolfe in the aftermath of the flight chaos and ordered his organization to complete a full investigation into the incident to make sure lessons are learned.

“I have now received NATS’ report and, while I am pleased to see that the safety of passengers was protected, it’s clear we need to urgently understand why this issue was not discovered and fixed before it caused chaos," she said.

Alexander said she has tasked the Civil Aviation Authority to conduct an independent review to check NATS’ findings and investigate their investment plans to enhance resilience in the future, along with regulatory accountability.

The U.K. government owns 49% of NATS, making it the largest shareholder and giving it a veto over key decisions. Airlines, airports, investors and employees own the remaining shares in the public-private partnership.