The UK air traffic control outage that disrupted hundreds of thousands of passengers last week was caused by a software defect, according to air traffic control operator NATS.
The failure resulted in around 2,000 flight cancellations and several days of disruption. Airlines faced significant costs as they worked to reposition aircraft and crews, while also dealing with passenger refunds and other arrangements.
NATS chief executive Martin Rolfe said the incident was not connected to the major disruption experienced in 2023. He also rejected reports suggesting that military intervention had played a role.
Rolfe said safety was never compromised during the latest outage.
Small Section of Software Caused Failure
According to NATS, the problem was traced to a small section of code within a specific part of its flight data system.
The company said the issue has now been identified. Temporary measures have also been introduced while engineers work on a permanent solution.
That fix will undergo safety testing before it is deployed, NATS said.
The technical failure was triggered when the system received a request for an identification code from an aircraft. A higher-priority request then arrived and paused the original request.
The NATS report said the system would have completed the update normally if the second request had arrived just one millisecond earlier or later.
Government Orders Independent Review
Transport Minister Heidi Alexander described the disruption as “completely unacceptable.” She had previously ordered NATS to produce a report explaining what happened.
Alexander also requested an independent review by the Civil Aviation Authority. She said the government needed to understand why the software problem had not been identified and fixed before it caused widespread disruption.
The minister added that the incident raised questions about the reliability of critical national infrastructure.
NATS Faces Pressure After Previous Failures
The latest outage has renewed scrutiny of NATS following earlier technical problems.
A major failure in August 2023 caused widespread travel disruption and reportedly cost airlines around £100 million. Another technical problem in July 2025 resulted in about 150 cancellations.
Ryanair, Europe’s largest airline, has repeatedly called for Rolfe to resign over the 2023 incident.
For now, NATS says the latest software problem has been identified and temporary safeguards are in place. The permanent fix will be introduced after safety testing is completed.
The government-ordered review is expected to examine the causes of the failure and whether further measures are needed to prevent another major disruption.
