Flight chaos caused by 'millisecond' software defect, report says

An air traffic control failure that sparked widespread travel chaos earlier this month was caused by a "software defect" affecting the system underpinning UK air space management, the national air traffic service Nats has said.

The problem happened "in the space of a millisecond", Nats said, leading to the system producing corrupted data.

The failure led to more than 2,000 flights being cancelled and hundreds of thousands of passengers affected, with some sleeping on airport floors or getting stuck overseas.

Transport Secretary Heidi Alexander called the disruption "completely unacceptable", while industry body Airlines UK is writing to Nats to demand immediate compensation for costs incurred.

The incident prompted questions over the resilience of Nats' systems, and some airlines questioned the position of its chief executive Martin Rolfe.

There has also been anger from passengers about how much support they got from airlines, and about the fact that they are unlikely to be entitled to compensation because the regulator judges the situation was extraordinary circumstances.

In an initial report , external , Nats said the software defect meant air traffic controllers had reduced information available, so restrictions were put in place to limit air traffic to maintain safety.

The defect occurred at 10:00am on 8 September, but it did not become apparent this was a serious problem for another two and a half hours.