NATS blames software defect for UK air traffic outage that cancelled 2,000 flights

Software defect triggers shutdown

A preliminary investigation by National Air Traffic Services published on 18 September 2026 determined that a coding defect caused the six-hour airspace shutdown on 8 September. The failure occurred when the National Airspace System received a higher-priority request while processing a manual identification code for an aircraft. When the system resumed the initial request, the software fault corrupted flight data in the space of a single millisecond. The technical report stated that if the second request had arrived even one millisecond earlier or later, the data update would have completed normally. NATS ruled out cyberattacks, hostile foreign sabotage, and military interference as potential causes for the disruption. Chief executive Martin Rolfe stated that safety remained intact throughout the event while teams introduced interim mitigations.

“This was a software issue in a specific part of our flight data system, that we have traced to a small subsection of coding.”

Operational breakdown and airport disruption

The software error initially appeared at 10:00 local time and was reported to engineers for investigation. The system seemed to function normally until 12:30, when the issue recurred and escalated to ground flights across the country. Controllers imposed flow restrictions across British airspace to maintain traveler safety, with the glitch preventing automatic radar identification codes from generating for subsequent flights. The operational halt primarily affected flight plans handled by the London control centre before spreading across the wider transport network. More than 2,000 flights were cancelled over two days, grounding aircraft across the United Kingdom and internationally. Disruptions centred on London Heathrow, with secondary cancellations recorded at Gatwick, Edinburgh, Birmingham, Liverpool, and Dublin.

Passenger impact and airline reactions

According to figures from the industry body Airlines UK, the two-day disruption affected more than 330,000 passengers across international routes. Approximately 155,000 travelers saw their flights cancelled outright, while another 180,000 experienced extended delays before flight schedules normalised. Airlines faced millions of pounds in unplanned costs to reposition aircraft, reassign stranded flight crews, and process customer refunds. EasyJet chief executive Kenton Jarvis urged aviation regulators to establish financial protections so carriers avoid bearing the full economic burden of system failures. Ryanair operations director Neil McMahon rejected technical excuses from the operator, while the airline repeated its calls for the resignation of the NATS chief executive.

“Passengers deserve more than just a promise that lessons will be learned. Firm action must be taken... and there must be a fair solution to ensure airlines do not have to bear the costs.”

Cancelled flights155,000

Delayed flights180,000

Cancelled flights

155000 passengers

Delayed flights

180000 passengers

Data from the article text

Regulatory review and recurring failures

The shutdown marked the third notable technical disruption linked to NATS since summer 2023. An August 2023 flight planning system collapse cost commercial airlines £100 million, while a July 2025 technical problem led to 150 cancellations. Transport Secretary Heidi Alexander requested the preliminary report from the operator and commissioned an independent inquiry led by the Civil Aviation Authority. The aviation regulator will independently verify the software findings and examine the broader resilience of UK navigation infrastructure. The independent investigation is scheduled to deliver its formal conclusions and safety recommendations within six months.

“We need to urgently understand why this issue was not discovered and fixed before it caused chaos.”