Flight chaos caused by software defect, says air traffic control bodyImage source, Dan Kitwood/Getty ImagesImage caption, Thousands of passengers were delayed by the NATS outageByKaty Austin, Transport correspondent and Tom Espiner, Business reporterPublished18 September 2026, 13:40 BSTUpdated 9 minutes agoAn air traffic control system failure that sparked widespread travel chaos earlier this month was caused by a "software defect", the UK's National Air Traffic Services (Nats) has said.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.Flights in and out of the UK's main airports were affected, including Heathrow, Gatwick, Luton and Glasgow.The incident prompted questions over the resilience of Nats' systems, and some airlines questioned the position of its chief executive Martin Rolfe.The government had previously ruled out a cyber attack, and last week the Ministry of Defence denied a report that a military aircraft was to blame.In an initial report, Nats said the defect happened in the system which "underpins the management of UK airspace".The problem happened "in the space of a millisecond", Nats said, leading to the system producing corrupted data.Air traffic controllers then had reduced information available, so restrictions were put in place to limit air traffic to maintain safety.Related topicsLondon Heathrow AirportTravel