The order, issued around 4 p.m. Eastern, cited "extraordinary circumstances" and was lifted later that evening, allowing departures to resume. Inbound international flights were being handled on a case-by-case basis while the stop was in effect, according to an FAA advisory.

Transportation Secretary Sean Duffy said technicians traced the disruption to a communication issue in which routers within what he called an "incredibly old" system became overloaded. At the time the stop was ordered, roughly 3,500 planes were in the air, he said.

"Because of that, we shut them down," Duffy said at a news conference.

Duffy directed his frustration at Congress, saying the Trump administration had spent at least a year seeking full funding for a new air traffic control system. He estimated a complete overhaul would cost about $50 billion.

"How many times does this have to happen before Congress gives the money to fix it?" Duffy said. "America, when do you want to start building a brand new system? Give us the money and let us finish the build."

Homeland Security Secretary Markwayne Mullin echoed that call, framing the aging infrastructure as a national security concern. He said the president had declared the matter a national emergency and urged lawmakers to act.

"We just saw what took place when we have vulnerabilities and when we have an old system," Mullin said. "This is what happens when Congress kicks the can down the road."

Mullin sought to reassure the public shortly after the stop was imposed, stressing that the halt was not the result of an attack.

"There is no fear to the public," he said. "This isn't another 9/11. I just can't repeat that enough. People are making that assumption because that's the last time we had a nationwide ground stoppage. This is a telecommunication outage. This is much different."

He said there was "zero" evidence of a cyberattack but that investigators were not prepared to rule one out entirely. Asked whether the stoppage was connected to a widespread Microsoft outage that disrupted users globally on Thursday and Friday, Mullin said he saw no reason to link the two.

"Those are separate issues," he said.

It was only the third ground stop of this magnitude in recent aviation history, following the Sept. 11, 2001, attacks and a January 2023 halt caused by an outage of the Notice to Air Missions system, which delivers pre-departure safety briefings.

The disruption came just three days after the FAA expanded its AI-supported Strategic Management of Airspace system, known as SMART, to all 22 air route traffic control centers. The tool combines roughly 200 data streams — including flight, schedule and weather information — to help anticipate airspace constraints.

At airports nationwide, travelers faced hours of uncertainty as departures were frozen. Video from terminals showed planes parked at gates and crowds of passengers waiting for information, many scrolling on their phones or watching flight boards. The FAA urged passengers to check with their airlines for flight-specific updates.

The episode put a fresh spotlight on the condition of the nation's air traffic infrastructure and the funding fight over modernizing it, a debate now unfolding against the backdrop of a presidential emergency declaration and mounting pressure on Congress.