Less than two weeks after a major failure in the NATS flight plan processing system, UK air traffic control faced another serious disruption. On Sunday, September 21, a connectivity failure at the Prestwick control center in Scotland caused delays and cancellations in northern England and Northern Ireland. The Prestwick center, which handles air traffic for Scottish operations, experienced a network problem early Sunday, prompting NATS — the UK provider of en route air traffic control — to temporarily limit the number of flights. Engineers worked to resolve the issue while implementing flow regulations to ensure safety. Initially, NATS said airports south of Manchester were unaffected, but flights to northern England and departures from Scotland faced delays. Major airports like Manchester, Glasgow, Edinburgh, Belfast, and Liverpool saw disruptions, with additional effects at London-Gatwick and London City due to aircraft rotations and traffic restrictions. The incident was resolved by the morning. NATS emphasized that the Prestwick failure was unrelated to the earlier incident on September 8 at the Swanwick control center in Hampshire. This time, the issue was a connectivity problem specific to the network used for Scottish operations, and NATS has not publicly detailed the exact affected component. The earlier failure on September 8 had a broader national impact, as a problem in the National Airspace System — the system that processes flight data — caused controllers in the London Area Control to lose part of their real-time flight information. They then switched to degraded procedures, requiring more manual coordination with neighboring control centers. While controllers still had access to radar and radio, the increased workload led to a significant reduction in the number of aircraft allowed into affected sectors. The preliminary NATS report suggests that the Prestwick failure was caused by an unknown and previously undetected software defect in a module that assigns or reassigns transponder codes — known as « squawks » — which allow aircraft to be identified by control systems. The very specific combination of events that triggered the failure occurred over a window of about one millisecond. NATS has ruled out human error, military action, or cyber causes at this stage. The impact of these incidents highlights the systemic nature of such failures. On September 8, NATS expected to manage around 8,000 flights but only processed 6,094, with over 2,000 flights delayed, canceled, or rerouted. The Prestwick failure, though more limited, still resulted in at least 24 flight cancellations in the morning, and Ryanair reported that 25,000 of its passengers were affected by delays. It is important to distinguish between safety and service continuity. In both incidents, backup mechanisms were used to ensure safety. When automation or available data cannot maintain normal operations, air traffic controllers reduce traffic, increase separation between aircraft, and use manual procedures. While this is costly for airlines, it is a core principle of safety systems: prioritizing safety over capacity. NATS confirmed that during the September 8 incident, all aircraft remained at a safe distance, and safety margins were maintained. However, the repetition of such incidents has raised concerns about the reliability of NATS systems. EasyJet stated that the new disruption calls into question the resilience of NATS systems and requested firm measures to prevent repeated failures. Ryanair renewed its call for the removal of NATS chief executive Martin Rolfe. The Civil Aviation Authority (CAA) reminds passengers that standard compensation is not available for delays or cancellations caused directly by external incidents beyond the airline’s control. However, airlines are still required to provide assistance, including information, food, accommodation if needed, and rebooking depending on the situation. NATS manages more than 2.5 million flights annually, with a significant portion of transatlantic traffic passing through UK airspace. A final report on the September 8 failure must be published within sixty days.