NATS review explained: What will the CAA investigation examine?

The UK Civil Aviation Authority is investigating whether NATS’ systems, investment plans and ability to recover from major failures are sufficient to keep UK air traffic moving. Its review reaches from the causes of September’s disruption to the future of the country’s air traffic management infrastructure, including whether the regulator’s own oversight has been effective.

Transport Secretary Heidi Alexander ordered the independent review after the 8 September failure, which delayed, cancelled or diverted more than 2,000 flights. The CAA published its terms of reference on 25 September and says the inquiry will also take account of a separate NATS fault at Prestwick on 21 September.

An initial report is due by the end of January 2027, with a final report to be delivered to the Transport Secretary by 8 March 2027.

“In recent weeks, passengers and airlines have been let down too many times, and I’m determined to get to the bottom of why,” Alexander said. She wants to know both what went wrong and whether NATS is prepared for the future.

What will the CAA investigate at NATS?

The CAA will assess NATS’ preliminary account of the 8 September failure, then look beyond the immediate software fault. Its remit covers plans to renew and replace critical operational systems, the adequacy of business continuity arrangements for systems still in use, and NATS’ ability to deliver its modernisation programme.

The review will also ask whether NATS has the leadership, skills and capacity to deliver those changes, and how its ownership structure influences investment and system renewal. That puts the organisation’s ability to replace ageing infrastructure under scrutiny alongside the reliability of the technology already in use.

It will consider how the UK air traffic network responds when capacity has to be reduced. Restricting the number of aircraft entering affected airspace keeps operations safe, but it can leave airlines with aircraft and crews out of position long after engineers restore the system.

As AGN’s explainer on air traffic control failures describes, fixing the fault is only the beginning of recovering a flight schedule.

The review will seek lessons from international practice on resilience and recovery. The CAA plans to hear from NATS, airlines, airports, passenger groups and other stakeholders, while an independent challenge panel will scrutinise its work.

Why is NATS under review by the CAA?

The immediate trigger was the failure at NATS’ Swanwick centre on 8 September. In its preliminary report, NATS traced the incident to a previously unidentified software defect in the processing of a manual aircraft squawk-code request. A second, higher-priority request arrived during a window of about one millisecond; when the first task resumed, the software processed it incorrectly and corrupted flight data.

NATS restricted traffic while engineers restored the affected system. Normal operations resumed about six hours after the initial failure, although cancellations and delays continued into the next day. NATS says it has introduced an interim mitigation while a permanent fix undergoes safety testing.

Then, on 21 September, a connectivity fault at NATS’ Prestwick centre affected a flight data processing system and prompted traffic restrictions across parts of Scotland, Northern Ireland and northern England. NATS says the two failures had different causes. The CAA has nevertheless confirmed that the Prestwick incident will inform its review.

There is a longer history behind the inquiry. A major NATS flight-planning failure in August 2023 affected around 700,000 passengers. The subsequent independent review made 34 recommendations covering NATS, the regulator, airlines, airports and government. The new investigation will examine how well recommendations from previous reviews have been implemented.

Why will the CAA investigate its own oversight?

The terms of reference explicitly include the effectiveness of the CAA’s regulatory oversight arrangements. That makes the review broader than an examination of NATS’ engineering decisions: it must also ask whether the regulator had enough visibility of risks to critical systems and whether its supervision encouraged adequate investment and contingency planning.

By June 2026, the CAA had confirmed that all 34 recommendations from the previous review had either been completed or incorporated into its ongoing regulatory work, according to a government parliamentary answer published in September. The new review will examine whether those measures were effectively implemented and remain adequate to address major disruption.

The CAA will appoint an independent challenge panel, subject to the Transport Secretary’s approval, to provide expert scrutiny. Its findings will need to show whether the measures taken since 2023 work in practice and what further changes are needed to prevent a technical fault from causing prolonged disruption across UK aviation.

When will the CAA publish its NATS findings?

An initial report is due to reach the Transport Secretary by the end of January 2027, with the final report due by March 8. The review can recommend urgent improvements before the initial report is published.

Its final recommendations will cover immediate action, improvements over one to three years, and longer-term renewal over three to 10 years.

The review will not determine legal liability or decide whether enforcement action should be taken over the September 8 incident. Any such decisions would follow separate regulatory processes.