By Will Guisbond, Sri Taylor, Courtney Subramanian and Jeff Mason

US authorities lifted a nationwide ground stop that disrupted thousands of flights and stranded passengers across the country, clearing the way for airlines to resume operations after more than four hours.

The Federal Aviation Administration halted flying on Friday after a data overload crippled air traffic control communications and radar, the agency said, in an incident that laid bare the frailty of America’s crucial aviation infrastructure.

The ground stop was lifted at 8:15 pm Friday evening. Airlines now face the challenge of restoring their schedules after the shutdown, with delays and cancellations potentially rippling through the system as carriers work to get aircraft and crews back into position.

It is unclear how long it will take the nation’s air travel to recover.

“Our switches, our routers, actually got overloaded with data, and they went down,” Transportation Secretary Sean Duffy said in a news conference. “And I shouldn’t say they went down. They started to give us inconsistency in the data from those routers. And because of that, we shut the system down.”

The rare nationwide halt, only the third in US history, came as the FAA grapples with aging air traffic control infrastructure and mounting pressure to modernize its systems. The agency had initially ordered all departing flights to remain grounded until further notice, citing extraordinary circumstances and safety concerns.

As of 9.15 p.m. New York time, almost 6,500 flights had been canceled and some 8,800 delays were delayed in, out and within the US, according to tracker FlightAware.

“It’s going to take us some time to unwind what’s happened this afternoon,” Duffy said. He later added, “I think we’re going to be back up and operational as we come into the heat of travel during Thanksgiving.”

The transportation secretary sought to reassure air travelers it’s safe to fly — insisting the US has “the safest system in the world” — even as he refused to rule out a similar air traffic control outage happening in the future.

“Is this exact thing going to happen again? I don’t know that this exact scenario will happen,” he said.

Homeland Security Secretary Markwayne Mullin told reporters that the FAA was “putting patches into the system” and the “new technology” was “overwhelming the older system.”

Duffy said earlier Friday that the communications issue affected all air route traffic control centers, which manage aircraft flying at high altitudes. The FAA attributed the disruption to a temporary telecommunications outage, though the precise cause remained under investigation.

“We had over 3,500 airplanes in the air,” Duffy told reporters. “They all engaged, and last time I looked, we had less than 400 in the airspace as they were all coming in to safely land, and we navigated it with our well-known procedures that we have when these incidents happen.”

Duffy said that controllers had “intermittent communication and intermittent radar,” allowing them to bring planes down safely.

The Trump administration is asking Congress for $50 billion in emergency funding to help update the nation’s air traffic control system, Duffy said. 

“I can’t build things if I don’t have money,” he added.

Mullin said “there is nothing that indicates” that the outage was caused by a cyberattack or a rogue artificial intelligence incident. Federal investigators were examining whether a software update may have triggered the disruption, a person familiar with the matter said before the press conference.

“I don’t want to rule out that we didn’t have nefarious activity here,” Duffy told reporters. “We’re still working on the details of what went wrong today.”

The shutdown marked the third nationwide ground stop in US history, following a 2023 outage of the FAA’s safety notification system for pilots and dispatchers and the Sept. 11 terrorist attacks in 2001.

The disruption comes as the FAA undertakes a sweeping modernization of its aging air traffic control infrastructure, backed by $12.5 billion in funding from Congress. Duffy has sought an additional $30 billion for the effort, with the Transportation Department renewing that request this week.