A tiny coding error froze London’s air‑traffic hub on September 8, leaving hundreds of thousands of passengers stranded. NATS now offers a first look at what went wrong and how safety was restored.
Nats disclosed that a software defect caused a major loss of flight data at the London Area Control centre at 09:30 GMT on Tuesday 8 September, forcing nationwide restrictions and widespread delays in the UK.
That disruption and a subsequent connectivity incident at the Prestwick centre in mid-September affected hundreds of services and drew direct intervention from the Secretary of State for TransportHeidi Alexander.
Ultimo aggiornamento: 23 September 2026
Why the finding matters and political response
The incident interrupted the National Airspace System (NAS) data stream that assigns flight identification codes used by radar to track aircraft in real time, compelling controllers to limit departures and arrivals to protect safety.
The decision to impose nationwide limits stemmed from the need to restore integrity across the NAS after corrupted data sets were detected.
Transport leadership signalled urgency: Heidi Alexander confirmed plans to meet the Nats board chair, Sir Warren East, after a “full and frank conversation” with chief executive Martin Rolfe.
The Prime Minister, Andy Burnham, said the issues “need to be fully investigated” and the transport secretary would “get to the bottom of what is behind this and why there has been a recurrence.”
Technical root cause and immediate operational measures
The provisional investigation found the trigger was a minute-scale software defect within a narrow fragment of Nats’ flight-data system responsible for assigning identification codes. A manual-entry processing routine was interrupted by a higher-priority message while awaiting completion; a hidden defect prevented correct re-initialisation and produced corrupted output that cascaded into subsequent flight-data updates.
The malfunction occurred within a single millisecond but degraded the flow of critical information to controllers. Nats said it applied a temporary mitigation and performed a full NAS reboot to reload affected data streams, restoring normal operations in the evening of 8 September though passenger backlogs persisted for more than 48 hours.
Follow-on outage at Prestwick and immediate effects
A second incident at the Prestwick centre later in September was described by Nats as a “connectivity issue” in the system network and lasted a few hours. The follow-on problem forced the cancellation of roughly 170 to 200 flights by mid-afternoon, affecting carriers including EasyJet, British Airways, Wizz Air UK and Ryanair.
EasyJet recorded the heaviest operational impact with 47 cancelled departures, while British Airways reported 11 cancellations. Major airports, including Heathrow in west London and Edinburgh, experienced blanked departure boards and stranded passengers. Airlines and industry groups demanded accountability and clearer remediation timetables.
Accountability, historical context and planned investment
Chief executive Martin Rolfe apologised and accepted responsibility for the September 8 incident, stressing that safety was never compromised. The provisional report explicitly stated the 8 September failure bore no relation to the August 2023 outage that affected the network during a bank holiday, nor to any form of military interference.
Over the past decade, Nats has invested more than £1 billion in technology modernisation. The Civil Aviation Authority plans to seek an additional £1 billion of funding by the close of 2033 to strengthen resilience and harden systems against similar failures.
The government holds a 49% stake in the organisation. That ownership and a record of several high-profile collapses in recent years — including an August bank-holiday outage in 2023 that stranded roughly 700,000 passengers — have intensified scrutiny of operational governance and future investment plans.
Industry reaction included calls for senior accountability. One airline executive publicly urged leadership change, arguing the repeated failures represented a “national confidence crisis.” Nats said it would implement a permanent, safety-certified software fix and roll it out in stages while the comprehensive final analysis continues.
The Civil Aviation Authority has described the case as subject to regulatory review and signalled it would consider both technical remediation and governance outcomes. Travel disruption rules and compensation frameworks remain under examination as airlines and passenger groups quantify the commercial impacts of the September incidents.
Further meetings between the transport secretary, Nats’ board and industry stakeholders are scheduled in the coming weeks as part of an ongoing inquiry into the causes, consequences and corrective roadmap.
