How a ‘millisecond’ software glitch caused six hours of chaos across UK airports

A software defect that occurred “in the space of a millisecond” triggered a six-hour UK air traffic control outage that disrupted hundreds of thousands of passengers, National Air Traffic Services has said.

The failure on September 8 initially stopped departing flights around London before disruption spread across the UK and beyond, causing widespread cancellations and delays.

A preliminary report found thhe problem occurred in software used to allocate identification codes to aircraft on radar.

While one aircraft code request was being processed, another request interrupted it.

When processing resumed, the software failed to restart correctly and corrupted subsequent flight data.

“This happened in the space of a millisecond,” the report said, according to The Guardian.

NATS chief executive Martin Rolfe said the problem had been identified and temporary measures were in place while a permanent fix underwent safety testing.

“I would like to apologise again, very sincerely, to everyone who was affected last week,” Rolfe said.

Transport Secretary Heidi Alexander said the disruption was “completely unacceptable” and the Civil Aviation Authority would examine the reports’ findings.

Ministers said they still needed “to urgently understand why this issue was not discovered and fixed before it caused chaos”.

Restrictions lasted six hours, while airlines took more than two days to clear the resulting passenger backlog.