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.
Professor John McDermid OBE FREng, Lloyds Register Chair of Safety at the University of York and a Fellow of the Royal Academy of Engineering, says:
“The Preliminary Report on the NATS Outage on 8th September 2026 gives a little insight into the underlying cause of the problem – a fault in legacy code which was exposed by processing being interrupted by a higher priority task; this gave rise to data corruption, then repeated accesses to corrupted data led to the system being shut down, with the widely-reported impact on flights. The report says that the problem arose because of timing – if the interruption to the processing had occurred a millisecond earlier or later then the failure would not have occurred. While this might seem ‘unlucky’, techniques for managing interactions between code of different priorities are well-known and would be expected to avoid this form of data corruption.
“NATS plans to undertake a Major Incident Investigation, and the Civil Aviation Authority (CAA) has also said it will undertake a review. While it is important to consider the direct cause of the incident, and its rectification, a more systemic review is needed. NATS depends on legacy systems, in some cases decades old. Replacing such systems is costly, and not without risk – but the longer they remain in service, the harder they are to replace as more systems are built on top of them and access to developers of the original code becomes less practical. Thus, the reviews need to consider how NATS migrates to more modern and more easily manageable systems, including considering the challenges of updating and replacing software in a highly complex system that must operate continuously. However, this requires a depth of insight that was missing from the analysis of the 2023 NATS outage.
“There is currently considerable concern about the use of AI in critical national infrastructure (CNI), such as air traffic management – this incident makes clear that it is also important to address the role of more conventional software on which all CNI depends.”
Notes for editors
The Royal Academy of Engineering creates and leads a community of outstanding experts and innovators to engineer better lives. As a charity and a Fellowship, we deliver public benefit from excellence in engineering and technology and convene leading businesspeople, entrepreneurs, innovators and academics across engineering and technology. As a National Academy, we provide leadership for engineering and technology, and independent, expert advice to policymakers in the UK and beyond. Our work is enabled by funding from the Department for Business, Innovation, Science and Trade, corporate and university partners, charitable trusts and foundations, and individual donors.