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NATS publishes preliminary report on technical incident of 8 September

Recorded: Sept. 18, 2026, 3:08 p.m.

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NATS publishes preliminary report on technical incident of 8 September - NATS

 

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NATS publishes preliminary report on technical incident of 8 September
18 September 2026

NATS, the UK’s major provider of air traffic services, has today published a preliminary report into the events which led to widespread disruption to travellers earlier this month.
This initial report was requested by Heidi Alexander, Secretary of State for Transport. It describes what caused the problem and its resolution, with a full report to follow.
Martin Rolfe, Chief Executive Officer, confirmed that this incident was unrelated to the major system outage in August 2023. He also dismissed speculation that it was caused by military intervention.
“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 said. “The issue has been identified and mitigation is in place while a permanent fix is safety tested and deployed.”
The preliminary report reveals that the incident on Tuesday 8 September was caused by a software defect in a small part of the National Airspace System (NAS), which underpins the management of UK airspace. The software in question allocates codes to individual aircraft when manual requests are made; these are usually allocated automatically. These codes are used to identify flights on radar when they are airborne.
While a manual request for an aircraft code was being processed, the system received a message for a higher priority activity which resulted in the aircraft code request being paused. When processing of the aircraft code request resumed, the software defect meant it did not resume correctly and the resulting output was corrupted, and affected some subsequent flight data updates. This happened in the space of a millisecond.
With reduced information available to controllers, restrictions were put in place to limit air traffic to maintain safety. Although the software issue only affected flights in the London Area Control centre – higher level flights operating mainly above 24,500ft – the restrictions had to be placed across the UK so that the NAS could be restarted and flight data reloaded.
Restrictions were in place for some six hours and while NATS operations returned to normal the same evening, it took more than two days for the backlog of passenger disruption to be cleared, with hundreds of thousands of passengers’ travel plans disrupted.
Mr Rolfe said: “I would like to apologise again, very sincerely, to everyone who was affected last week. It’s our job to get people where they want to go, quickly and without delay and we are devastated when that goes wrong. However, our primary role is to keep our skies safe, and everyone who flies through them. At no point last week was safety in question.”
Over the past 10 years, NATS has invested well over one billion pounds in systems and technology, and we will soon submit plans to the Civil Aviation Authority to invest a further billion pounds by the end of 2033.
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Read the preliminary report here

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NATS, the UK’s principal provider of air traffic services, released a preliminary report concerning a technical incident that caused widespread disruption to travelers earlier in September. This initial report was commissioned by Heidi Alexander, the Secretary of State for Transport. Martin Rolfe, the Chief Executive Officer, stated that the incident was not related to the major system outage that occurred in August 2023, nor was it caused by military intervention. Rolfe further explained that the root cause was identified as a software defect within a small segment of the National Airspace System (NAS), which is fundamental to managing UK airspace.

The specific mechanism of the failure involved the system's handling of aircraft codes. These codes are used to identify flights on radar when manual requests are made, although they are usually allocated automatically. The software defect manifested when a system received a message for a higher priority activity while processing an aircraft code request, causing the request to pause. When processing resumed, the defect resulted in corrupted output and incorrect subsequent flight data updates, which occurred within a fractional amount of a millisecond.

Due to the reduced information available to air traffic controllers, safety restrictions were immediately implemented to manage air traffic flow. Although the software issue was localized to the London Area Control centre, affecting higher level flights operating above 24,500 feet, these restrictions had to be extended across the entire United Kingdom to facilitate the restart of the NAS and the reloading of flight data. These restrictions remained in place for approximately six hours. Following the restoration of normal NATS operations that evening, it took more than two days to fully clear the backlog of passenger disruptions. Mr Rolfe apologized to all affected parties, emphasizing that while the disruption was significant, safety was never compromised during the event.

NATS highlighted its commitment to technological advancement and safety, noting that over the last decade, the organization has invested more than one billion pounds in systems and technology, and plans to submit proposals to the Civil Aviation Authority for an additional billion pounds in investment by the end of 2033. The incident underscores the critical nature of the complex digital infrastructure that underpins air traffic control and the importance of maintaining system reliability for public safety.