More than 250 flights were cancelled today, 19 September 2026, at Heathrow and Gatwick airports due to an outage caused by a software defect in the UK’s air traffic control system operated by NATS.
Cause of the Outage
NATS traced the problem to a small subsection of code within their flight data system. The outage resulted from a timing conflict between two system requests, where a higher-priority request interrupted a lower-priority one, preventing completion. NATS explained that if the higher-priority request had arrived even one millisecond earlier or later, the system would have functioned normally.
Mitigation and Official Responses
NATS CEO Martin Rolfe confirmed that safety was never
compromised during the incident and stated, “The issue has been identified, and mitigation is in place while a permanent fix is safety tested and deployed.” UK Transport Minister Heidi Alexander described the disruption as “completely unacceptable” and demanded a report and an independent review by the Civil Aviation Authority. She emphasized the urgent need to determine why the defect went undetected before causing operational chaos and stressed that “It is crucial that our national infrastructure is fit for the future.”
Context and Passenger Impact
This is the latest in a series of air traffic control disruptions in the UK: a shutdown in August 2023
caused £100 million in airline losses and resulted in widespread cancellations, while a technical problem in July 2025 led to 150 flight cancellations. Ryanair has repeatedly called for Martin Rolfe’s resignation since the 2023 failure. The current outage has disrupted operations at Heathrow and Gatwick, forcing airlines to rearrange crews and aircraft and process refunds for passengers affected by the cancellations.
