A technical issue with the UK's air traffic control system, managed by NATS, caused widespread disruptions at major airports including Heathrow, Gatwick, and Edinburgh, grounding flights across southern England shortly after 4pm UK time. 

Eurocontrol reported the London control area as "temporarily unavailable" due to a radar-related issue, though NATS confirmed systems were fully operational by 5pm. Despite the resolution, severe delays exceeding three hours and cancellations persisted, with Heathrow limiting flights to 32 per hour, resuming normal operations (45 per hour) by 7:15pm. NATS attributed the outage to a radar issue, quickly mitigated by switching to a backup system, and reduced traffic to ensure safety. No evidence suggests a cyber-related cause. 

Passengers faced significant disruptions, with many stranded on runways or at airports like Italy's Treviso, where a pilot reported London's air traffic control was "blocked." Social media and flight tracking maps showed aircraft clustered around London airports, with clear skies over southern England. 

Transport Secretary Heidi Alexander warned of ongoing disruptions, urging passengers to check with airports. London City Airport reported potential cancellations, while Gatwick noted delays as operations resumed. The outage drew sharp criticism, with Ryanair calling for NATS chief Martin Rolfe's resignation and Lib Dem leader Sir Ed Davey demanding an urgent investigation to ensure the system's reliability and rule out hostile actions. 

A Eurocontrol source described the radar failure as an isolated UK issue, with no outages reported in continental Europe. Passengers were advised to verify flight statuses with airlines as airports worked to clear backlogs. The incident highlighted vulnerabilities in critical infrastructure, prompting calls for greater resilience to prevent future disruptions, especially during peak travel periods.