More than 250 flights were cancelled on September 19, 2026, at London’s Heathrow and Gatwick airports due to a software defect in the United Kingdom’s air traffic control system operated by NATS.
Software Defect in Flight Data System Triggers Outage
The disruption was caused by a small coding error within a specific section of the flight data system software, according to NATS Chief Executive Martin Rolfe. The issue arose from a timing conflict between two system requests, where a higher-priority request paused the processing of another update. The technical report from NATS stated that if the higher-priority request had arrived even one millisecond earlier or later, the update
would have completed without incident.
Mitigation measures have been put in place while a permanent fix undergoes safety testing prior to deployment. NATS confirmed that safety was not compromised at any point during the outage.
Passenger Impact and Operational Consequences
The software defect disrupted air traffic control operations at Heathrow and Gatwick, leading to cancellations affecting over 250 flights. The cancellations caused significant operational challenges for airlines, including the reallocation of crew and aircraft resources and passenger refund processing. Similar disruption previously occurred last week when a NATS outage forced 2,000 flight cancellations.
Previous incidents include a major shutdown in August 2023 that resulted in
travel chaos and £100 million in airline losses, and a July 2025 technical fault causing 150 cancellations.
Official Responses and Investigations Underway
NATS CEO Martin Rolfe stated, “This was a software issue in a specific part of our flight data system that we have traced to a small subsection of coding,” adding, “The issue has been identified, and mitigation is in place while a permanent fix is safety tested and deployed.”
Transport Minister Heidi Alexander described the disruption as “completely unacceptable” and called for urgent investigation into why the defect was not discovered beforehand. She ordered an independent review by the Civil Aviation Authority and
emphasized, “It is crucial that our national infrastructure is fit for the future.”
Ryanair, Europe’s largest airline, has repeatedly demanded the resignation of NATS CEO Martin Rolfe following ongoing system failures affecting British airspace management.
