At a White House news conference, Transportation Secretary Sean Duffy insisted that the U.S. has the "safest airspace in the world" but also suggested an incident like Friday's ground stop would happen again and that flying will continue being “less safe” unless Congress provides funding for flight system advancement.

"We didn't think we would have this kind of outage," Duffy said. "The systems that were deployed kept everybody safe -- everyone landed. We're able to review what went wrong and then reboot the system and go. But you will have more of these. You will have more of them unless the American people and the Congress tell us to build."

Duffy called on Congress to provide $50 billion for a "complete overhaul" of the system.

Following the lifting of the ground stop, United Airlines said it is "resuming operations, including some planned Friday night flights."

Transportation Secretary Sean Duffy called for funding from Congress to upgrade what he called an "incredibly old air traffic control system" in the wake of Friday's nationwide ground stop.

"This is an emergency," he told reporters. "I want Congress to give us emergency funding. This is bipartisan. This is American. I want $50 billion."

In describing Friday's issue, Duffy pointed to "old switches, old routers."

"We use 1980s little copper lines. It's an old system that went down and went down everywhere. It got overloaded," he said.

"I think our fix gives us a pretty good indication that it was a legacy network problem that went down," he continued, adding, "By the way, all of the new equipment that we put in, none of that went down."

On how long to expect delays and cancellations due to the ground stop, Transportation Secretary Sean Duffy told reporters, "I believe that it's going to take us some time to get back to capacity."

He said, "it's going to take us some time to unwind what's happened this afternoon," adding that "hopefully tomorrow we are going to start to see far better movement."

Duffy said he believes things will be "back up and operational" heading into Thanksgiving travel.