US Transportation Secretary Sean Duffy said a legacy air traffic control communications system became overloaded and began issuing faulty data, prompting a nationwide “ground stop” on Friday that led to more than 10,000 cancelled and delayed flights.
This comes after the Federal Aviation Administration (FAA) grounded all departing US flights on Friday for just the second time since the 9/11 attacks in 2001, citing "extraordinary circumstances" caused by communications problems at regional air traffic control centres.
The agency described the problem as "a temporary telecommunications outage" and said it was acting "out of an abundance of caution." The ground stop for US flights, which halted thousands of departures and disrupted travel for hundreds of thousands of people, was lifted after almost four hours.
Deep Dive
Why did the FAA ground all departing US flights?
What caused the US air traffic control system to fail?
Was the FAA ground stop caused by a cyberattack?
What the US government said
Duffy attributed the outage to a problem with the FAA's “incredibly old” legacy network.
"Our switches, our routers, actually got overloaded with data... They started to give us inconsistency in the data ... and because of that, we shut the system down," Duffy said at a White House briefing, adding it had intermittent communication and intermittent radar.
Homeland Security Secretary Markwayne Mullin said there was no sign of a threat to the United States and "this isn't another 9/11."
{{/usCountry}}Homeland Security Secretary Markwayne Mullin said there was no sign of a threat to the United States and "this isn't another 9/11."
{{/usCountry}}"There was no indication, as of yet, that this was a nefarious attack against us; it's just a telecommunications outage, as of right now," he said at a briefing, adding that officials had not ruled out anything at the point.
This was the first nationwide ground stop in the US since January 2023, when a key FAA computer system malfunctioned.
The shutdown came on the same day the White House and the Department of Transportation sought another $30.1 billion from Congress to upgrade airports and air traffic control, including $10.1 billion for air traffic control modernisation.
Problems well documented
The Government Accountability Office reported in 2024 that the FAA had classified 51 of its 138 air traffic control systems as unsustainable and another 54 as potentially unsustainable. Together, they accounted for more than three-quarters of the systems reviewed.
FAA Administrator Bryan Bedford told Reuters in September that the agency's more than 300 air traffic facilities operated as technological silos, relying in some cases on decades-old computers and telecommunications systems that cannot communicate seamlessly with one another.
Some obsolete equipment requires replacement parts obtained from online auction websites or manufactured via 3D printing.
The US Congress approved $12.5 billion in July 2025 to modernise the country's ageing air traffic control infrastructure, including telecommunications and radar systems. The administration said Friday that 68% of the FAA's legacy copper telecommunications network had been replaced with high-speed fibre.
But Bedford warned in September that replacing ageing copper wires with fibre-optic cables alone would not prevent future outages without a modern telecommunications network.
The FAA aims to complete the first phase of modernisation by December 2028. But the GAO warned that inadequate planning increased the risk of delays, potentially leaving the agency dependent on outdated, failure-prone systems for longer.