A software defect in the United Kingdom’s air traffic control flight data system caused more than 250 flight cancellations at Heathrow and Gatwick airports during the week prior to September 18, 2026. The outage disrupted operations and affected hundreds of thousands of passengers flying through these two major UK gateways.
Technical Cause Identified by NATS
NATS, the British air traffic control operator responsible for the system, traced the issue to a small subsection of coding in the flight data system. CEO Martin Rolfe explained that the defect arose when a request for an aircraft identification code was interrupted by a higher-priority system request, causing the
first request to pause and ultimately fail. Rolfe said, “This was a software issue in a specific part of our flight data system, that we have traced to a small subsection of coding.” He added that a mitigation is now in place while a permanent fix undergoes safety testing and deployment.
Official Responses and Review Ordered
Transport Minister Heidi Alexander called the disruption “completely unacceptable” and demanded urgent investigation and infrastructure improvements. She stated, “We need to urgently understand why this issue was not discovered and fixed before it caused chaos. It is crucial that our national infrastructure is fit for the future.” The UK
Transport Ministry directed the Civil Aviation Authority to conduct an independent review of the incident. NATS CEO Rolfe reassured that safety was never compromised during the outage.
Operational Impact on Airlines and Passengers
The software outage forced airlines operating at Heathrow and Gatwick to cancel over 250 flights, resulting in major operational challenges including repositioning crew and aircraft and processing passenger refunds. The disruption affected hundreds of thousands of travelers and added strain on the airlines’ logistics and customer service resources.
This September 2026 incident follows earlier UK air traffic control disruptions, including a major outage in August 2023 that triggered 2,000 flight cancellations and cost
airlines millions of pounds. A smaller technical issue in July 2025 also led to 150 cancellations. Ryanair, Europe’s largest airline, has criticized NATS’ leadership since the 2023 disruption.
The NATS report specified that the root trigger was timing of a high-priority request relative to a flight data update request. According to the report, “Had the higher-priority request arrived even one millisecond earlier or later, the update would have completed normally.” The 2026 outage is unrelated to the 2023 incident and disproves rumors of military intervention.
