US Flights Resume After FAA Lifts Nationwide Ground Stop Caused by Communications Failure

At Chicago O'Hare on Friday afternoon, travellers who had just cleared security looked up at the departure screens and found delays listed across the board. That was how many of them learned the Federal Aviation Administration had ordered a nationwide ground stop. Some phoned friends or family to talk through whether to stay the night in Chicago or find another way to get where they were going.

The order, issued Friday afternoon, cited "extraordinary circumstances" caused by communications problems at regional air traffic control centres. It held aircraft on the ground for more than four hours and left tens of thousands of passengers waiting. Flights bound for the US from other countries were cancelled, while those already en route were allowed to land. Cargo was affected too. Airlines for America says US carriers move about 61,000 tons of goods, from letters to packages, to and from more than 220 countries every day.

The scale was large. According to the aviation analytics firm Cirium, more than 1.5 million passengers were scheduled to depart US airports on roughly 11,000 flights after 4 pm, shortly after the stop began. NBA, NHL and college teams were among those stranded while trying to reach their destinations.

The FAA has since lifted the order and airlines have begun resuming departures, but normal operations will not return immediately. So many planes and crews are out of position that the schedules will take time to untangle. International flights were being handled case by case, according to Homeland Security Secretary Markwayne Mullin, and some were seen taking off Friday evening.

The stoppage was the first nationwide ground stop since January 2023, when a key computer system malfunctioned, and only the second since the aftermath of the September 11 attacks. Federal officials have blamed such disruptions on overloaded and outdated systems. Speaking to reporters at the White House, Mullin said that introducing some new technology into an old air traffic control system had overwhelmed it.

The cause is not settled. Asked whether he could rule out a cyberattack or a rogue artificial intelligence incident, Mullin said: "There's nothing completely certain right now. It doesn't appear that way." He said there are no "footprints" pointing to an attack and that the failure appears to be "mechanically driven," adding that officials were still looking for the cause. He said investigators will examine whether there is any link to the FAA's nationwide rollout of a new artificial intelligence system meant to help identify problems and reroute planes.

The failure comes while the government is trying to modernise the technology controllers depend on. Congress approved $12.5 billion for the project last year. Miles of old copper wire have been replaced with fibre optic lines, and old radio systems are gradually being replaced at airports across the country. Transportation Secretary Sean Duffy says a further $US30 billion is needed to upgrade air traffic control.

Aviation safety expert Steve Arroyo said the problem looked similar to a regional air traffic control communication outage in September that snarled hundreds of flights across the Northeast, only this time on a national scale. He said it may be linked to the outdated technology controllers use.

The next things to watch are how quickly airlines reposition aircraft and crews, and what investigators conclude about the cause, including whether the new AI rerouting system played any part.