Hundreds of flights were grounded across the UK on Tuesday after a major software systems outage affected multiple airports including Gatwick and Heathrow.
UK air traffic control services provider NATS – which handles over 2.5 million flights yearly – said at 15:25 it had confirmed “the issue was in our flight processing system.”
By 16:40 it had implemented a fix and said “our flight system is starting to recover.”
The company added in a status update: “We are continuing to work closely with our airline and airport customers on recovery. We apologise sincerely for the disruption to people’s journeys today and they should continue to check with their airline.”
Dennis Martin, a crisis resilience specialist at operational technology (OT) firm Axians UK commented to The Stack: “Restoring the technical service is only the first step.
“Aircraft and crews are out of position and duty hours are running down, which means the disruption is likely going to last longer than the technical recovery.”
NATS also suffered incidents in August 2023, affecting more than 700,000 passengers, and again a more localised incident at Swanwick in July 2025. A Civil Aviation Authority (CAA) review of the 2023 incident, published in May 2024, urged fresh efforts on contingency arrangements and incident response by the company.
The 2023 incident saw a NATS software bug start generating “critical exception errors” that triggered firstly its primary air traffic control system and then the secondary system to enter maintenance mode, to prevent the transfer of bad flight data.
That, in turn, forced a halt to the automated processing of flight plan data and as the CAA noted, the “remaining processing capacity was entirely manual” cutting flight planning from “typically 800 per hour during a busy period to approximately 60.”
Ending the incident required the help of the system manufacturer, Germany’s Frequentis Comsoft which had “greater understanding of the interface between the two [disparate affected systems and] was key to identifying the root cause of the event,” the CAA said. A further NATS disruption occurred at Swanwick in July 2025.
Grilling NATS' CEO and COO after the 2023 incident, MPs on Parliament’s Transport Committee noted that the CAA report showed “a Level 2 engineer was not on site, and that having attempted to fix the problem it took an hour and a half for the engineer to arrive. The escalation protocols meant that the Level 3 engineer was not sought for more than three hours after the failure, which affected hundreds of thousands of people. The Level 3 engineer was unfamiliar with the fault message, so the software company was not contacted until four hours after the incident started.”
NATS CEO Martin Rolfe responded: “To give you a sense of the number of issues that they resolve, since 2016, when we started to measure in the way we currently do, 54,000 technical issues have had to be solved by that group of [on-site] engineers.
“About 99.98-something percent of those are solved by… people on site all the time.
“They are 365-rostered on and will actually be at the site.”
