Airlines canceled more than 100 flights across the UK on Wednesday after a "technical issue" with radar systems left air traffic controllers flummoxed.

Air traffic in London, Edinburgh, and other UK airports was severely disrupted, the UK's National Air Traffic Services (NATS) warned. Passengers faced long delays while planes queued up to take off from Europe's biggest air traffic hub. A NATS spokesperson told the [1]BBC that the failure was related to radar.

"As a result of a technical issue at NATS Swanwick air traffic control centre, we are limiting the number of aircraft flying in the London control area in order to ensure safety, which is always our first priority," the agency [2]said at the time.

[3]

Flight tracking service [4]Flightradar24 said that the entire London control area was closed for a period of time.

[5]

A person with working knowledge of the UK's air traffic control system speculated to El Reg that the outage was caused by a primary failure in radar systems, not in the backup monitoring system, but we're waiting on more information. In the meantime, the problem appears to have been resolved.

"Departures at all airports have resumed and we are working with affected airlines and airports to clear the backlog safely," NATS [6]said around 7pm UK time. "We apologise to everyone affected by this issue."

[7]UK air traffic mega cockup: BOTH server channels failed - report

[8]Datacenters near Heathrow seemingly stay up as substation fire closes airport

[9]REVEALED: Titsup flight plan mainframe borks UK air traffic control

[10]UK Civil Aviation Authority ponders vertiports for flying taxis

It could be worse. Earlier this year, Heathrow was knocked offline for nearly a day after a substation fire cut power to the airport. The blaze was traced to [11]moisture buildup in a high-voltage bushing , leading to a short circuit, an arc flash, and a fire.

This also doesn't look as serious as the 2014 NATS meltdown, when a corrupted line of code crashed both the main and backup flight‑data systems, leaving controllers without access to flight plans and forcing a temporary shutdown of London airspace. Air traffic control relies on [12]redundant servers to process flight data, but in that case, the failover failed too. ®

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[1] https://www.bbc.com/news/live/cewd49znze4t?post=asset%3A83494607-dd33-47cf-a38c-f2216adfade1#post

[2] https://www.nats.aero/statement/statement-technical-issue-at-swanwick/

[3] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/front&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2aIqV5zAeBIxAZGLNCQSZcwAAAE4&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0

[4] https://x.com/flightradar24/status/1950572091553566734

[5] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_offbeat/front&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44aIqV5zAeBIxAZGLNCQSZcwAAAE4&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0

[6] https://x.com/NATS/status/1950588789958844445

[7] https://www.theregister.com/2015/02/09/nats_air_traffic_issues_due_to_server_channels_failing_report/

[8] https://www.theregister.com/2025/03/21/heathrow_closure_datacenter_resilience/

[9] https://www.theregister.com/2014/12/12/iregi_confirms_it_was_dodgy_flight_server_that_took_down_uk_air_traffic_control/

[10] https://www.theregister.com/2024/01/25/uk_civil_aviation_authority_ponders/

[11] https://www.theregister.com/2025/07/02/moist_bushing_behind_heathrowclosing_conflagration/

[12] https://www.theregister.com/2014/12/12/iregi_confirms_it_was_dodgy_flight_server_that_took_down_uk_air_traffic_control/

[13] https://whitepapers.theregister.com/