PHILADELPHIA (WPVI) -- The Federal Aviation Administration said Friday night that airplane departures can resume after the agency lifted a nationwide ground stop that Trump administration officials blamed on "overloaded," "outdated" systems.

Even with the order being lifted, the airlines will not be able to return to normal operations immediately because so many of their planes and crews are out of position.

The FAA had grounded all flights nationwide Friday afternoon, causing hundreds of flights to be diverted. Officials cited "extraordinary circumstances" caused by communications problems at regional air traffic control centers.

FAA ground stop live updates: Duffy blames 'overloaded' routers; thousands of flights canceled

Homeland Security Secretary Markwayne Mullin told reporters at the White House that the introduction of some new technology into an old air traffic control system overwhelmed it. He couldn't rule out another outage.

The nationwide ground stop was the first since January 2023, when a key FAA computer system malfunctioned, and the second since the aftermath of the Sept. 11, 2001, attacks.

There was no indication the communications failure was related to a cyberattack. The consequences were profound, disrupting potentially thousands of planned flights through at least late Friday night and upending travel plans for passengers.

"It's frustrating. This certainly sounds like it's going to be more than the usual run-of-the-mill delay. I look forward to finding out why," said Jeff Dubner, a Washington attorney whose Alaska Airlines flight home from Los Angeles was already half an hour late and taxiing to the runway when the plane came to a halt.

International flights were being handled on a case-by-case basis, according to Mullin, with some seen taking off Friday evening.

Action News caught up with some travelers at PHL who were forced to pivot Friday night.

"It felt like a movie, honestly. And then when we got out inside the terminal, everybody just sitting there on their phones," said Cynthia Pecina, who is trying to get to Detroit.

"When they told us they had no idea how long it might be, I was like, OK, I have my cat with me, I definitely can't sit here like, I don't have food for him. I don't have water. So that's when I gave up," added Haley Brown, who rebooked her flight for Monday.

Despite the halted departures, several passengers decided to go through security and sit at their gates.

A family of six waited for an update for more than 10 hours.

"She got a really good nap. The rest of us have been eating food and wandering around the airport, trying to get our steps in," said Joseph Hammer of Wyoming.

Some travelers even got as far as their airplane seats before they were told to get off due to ongoing issues.

"I was excited, and now we're disappointed. It's no one's fault, but we're shocked," said Hiam Ascnyassine of Montreal.

As stranded passengers try to figure out when they can catch their next flight, they're staying positive.

"It happens. It's a part of flying," said Woodward.

Our own Alicia Vitarelli is at LAX and is having trouble getting back to Philadelphia.

"I will tell you that they just got over the intercom and told everyone these flights aren't going anywhere for the moment, as far as they're concerned. They're not going to be rebooking any of today's flights. They're just asking people to go ahead and make new reservations for tomorrow," Vitarelli said

There were long lines outside and inside car rental agencies as people were left figuring out what to do and where to go.

Out of sheer luck, Kevin Scott says he was able to secure one rental car.

His plans of flying home to Virginia from New Hampshire were scrapped after the ground stop.

"I abandoned my bag. Hoping when the dust settles I can get it shipped to the house," said Kevin Scott of Virginia Beach.

NBA, NHL and college teams were left stranded as they tried to reach their destinations. Meanwhile, NFL teams were left to wonder whether the issue would be resolved in time to travel to their games this weekend.

Most college football teams playing Saturday travel the day before their game, and the stoppage left many schools — including No. 2 Utah, eighth-ranked Texas and No. 9 Tennessee — at a standstill as they departed for road games.

Penn State is expected to face the University of Minnesota at home Saturday at 7 p.m.

"Penn State is in communication with the Big Ten Conference and the University of Minnesota. We will continue to closely monitor the situation and will share updates when available," the university said in a statement.

READ MORE: Penn State football game in limbo as ground stop disrupts travel for college teams

Mullin had said investigators will look at whether there is any link to the FAA's nationwide rollout of a new artificial intelligence system to help identify problems and reroute planes. But that system operates out of one location near Washington, D.C., and just sends recommendations to the air traffic control centers.

The government has been working to overhaul the outdated technology that air traffic controllers rely on since Congress approved $12.5 billion for the project last year. Miles of old copper wires have been replaced with fiber optic lines and old radio systems are gradually being replaced at airports across the country.

But much work remains. Transportation Secretary Sean Duffy has said that another $30 billion will be needed to complete the work, and the White House has begun lobbying Congress to approve it.

The problem appeared similar to a regional air traffic control communication outage in September that snarled hundreds of flights across the Northeast, aviation safety expert Steve Arroyo said, except this time on a nationwide scale. It may be linked to the outdated technology used by air traffic controllers.

"If you don't have that ability, whether it's because the old wires that they have are just run down or for whatever reason, you've got to stop airplanes on the ground," said Arroyo, who is a former United Airlines pilot. "And not put them in the air where you're going to risk not being able to communicate with them."

Friday's ground stop was different than the one after Sept. 11 because planes were not being told to land immediately and pilots likely were able to communicate with ground controllers at airports, Arroyo said.

Asked whether Mullin could rule out a cyberattack or rogue artificial intelligence incident, he said: "There's nothing completely certain right now. It doesn't appear that way." He said there are no "footprints" showing an attack and that it appears to be "mechanically driven," adding that officials were still looking for the cause.

At least 827 flights were diverted so far as a result. As of 7:05 p.m. EST, 670 flights were sent back to the airport from where they originally took off, while 157 were redirected to a different airport, according to Cirium, an aviation analytics company.

The airports where many of the flights ended up being diverted included Washington Dulles International Airport, Los Angeles International Airport, Cincinnati/Northern Kentucky International Airport and Nashville International Airport.

Some 11,000 flights carrying more than 1.5 million passengers were scheduled to take off from airports in the U.S. after 4 p.m. EST, raising the likelihood of more cancelations and flight diversions.

At Chicago O'Hare Airport on Friday afternoon, travelers passing through security learned about the ground stop when they looked up at screens that showed flight delays across the board.

Some called friends or family members, debating whether to stay the night in Chicago or find another way to their destinations.

Amber McQuilkin, 27, sat on a bench, disappointed that she might miss a trip with friends to New York for the League of Legends world finals. Her friends, she said, had already arrived there.

"There's not really any information being passed to me," said the Seattle software engineer, who took a week of vacation for the trip. "I contemplated just abandoning the flight and driving, but then the more I thought about it, the more I'm like, that would be miserable."

Austin Curtis and his wife were rethinking their trip from South Bend, Indiana, to a friend's baby shower in Denver after getting delayed during a layover in Chicago.

They had boarded a flight to Denver from O'Hare International Airport when they were told to get off the plane.

"We did see them taking luggage off our plane and others, so we're assuming it's going to be a pretty substantial delay," Curtis said.

They were unsure whether to get a hotel room or keep waiting out the delay at the airport. With care already in place for their two young children at home, they might stay the weekend in Chicago, he said.

The Associated Press contributed to this report.