America's Skies Fall Silent: Longest Nationwide Flight Grounding Since 9/11 Strands Millions

The United States grounded every departing flight in the country on Friday afternoon, in the longest nationwide shutdown of American airspace since the September 11, 2001 attacks, after a communications failure rippled through the air traffic control system. The Federal Aviation Administration imposed the stop after radar and communications at its control centres became unstable, and lifted it at 8:15 p.m. Eastern Time, more than four hours later — but by then the damage to the day's flying was done, and the disruption was still cascading into Saturday.

The scale of the shutdown was stark. More than 6,600 flights were cancelled on Friday and 8,600 delayed, according to Reuters, and aviation analytics firm Cirium counted 8,267 flights cancelled or never flown out of 26,284 scheduled departures — nearly a third of the day's flying. Almost 900 flights were diverted mid-air, and about 3,100 aircraft were already heading for American airports when the order came down, all of which had to be landed safely. The recovery was slow: more than 2,000 further flights were cancelled on Saturday as airlines tried to untangle crews and aircraft left in the wrong cities, with another 1,500 already cancelled for Sunday, and professional and college sports teams scrambled for buses and charter flights to reach Saturday's games.

Transportation Secretary Sean Duffy said the trouble began at 3:36 p.m., when switches and routers in the ageing air traffic control network became overloaded with data and began transmitting inconsistent information. The system still runs in part on TDM, a legacy analogue telecommunications technology, and Duffy said the failure struck the old equipment while the newer kit that has already been installed kept working. Two airline officials told reporters the outage appeared to affect a telecommunications network overseen by the defence contractor L3Harris Technologies, and investigators were also examining whether a software update had triggered the failure. The FAA has already replaced thousands of old copper lines with fibre optics and upgraded hundreds of radio systems since Congress approved $12.5 billion for the overhaul last year, but the modernisation is far from complete.

Officials were quick to rule out the darkest explanations, and slower to explain the failure itself. Homeland Security Secretary Markwayne Mullin said there was "zero evidence" so far of a cyberattack or a rogue artificial intelligence system, describing the outage as "mechanically driven", though he added that investigators had not ruled anything out. President Donald Trump said the failure appeared unlikely to be linked to a cyberattack or to AI, and was more probably caused by ageing, damaged infrastructure. The FBI does not view the incident as a cyberattack or criminal activity, according to reports, and Duffy stressed that the FAA's new AI-powered prediction system was not connected to the failure — though Mullin conceded that new technology being added to the system had been "overwhelming the older system", and the precise chain of events remains under investigation.

The political argument began almost as soon as the planes stopped. Duffy blamed Congress for failing to approve more funding for new technology, while downplaying the fact that the attempt to install new fixes had itself overtaxed the system. Critics noted that the administration was asking for about $50 billion for a full overhaul of air traffic control — a figure Duffy himself has cited — and questioned whether the failure was being used to force the money through. Online, the scepticism was loud: a thread on r/news announcing the ground stop drew more than 21,000 upvotes and 7,000 comments, and on Hacker News, where a thread on the stop drew more than 1,500 points and 1,100 comments, readers questioned how the cause could be identified so quickly before any investigation, and pointed to a similar FAA telecommunications outage in 2009. On Polymarket, traders gave an 89 per cent chance that investigators will confirm a problem with the FAA's SMART air traffic management system caused the stop.

The shutdown was only the second nationwide halt of all departures since 9/11, and the first since January 2023, when a computer system that sends safety notices to pilots malfunctioned. It also came on a day when a separate, major Microsoft 365 outage disrupted businesses, banks and pharmacies around the world, though officials said no connection between the two failures had been established. What happens next is a test of both the system and the politics around it: airlines have warned that cancellations and delays could persist for days as crews and aircraft are repositioned, passengers have been told to check with their carriers before travelling, and the investigation into what exactly overloaded the network — and whether the modernisation programme itself contributed — will now run alongside a renewed fight over the billions needed to rebuild the oldest parts of the system that guides America's skies.