Weary travellers braced for more delays and cancellations on Saturday as flights resumed from US airports after being grounded for four hours due to a major outage on outdated communications systems.

Friday’s nationwide stop sparked widespread chaos and left hundreds of thousands of passengers in limbo, with some pulled off planes moments before departure by airline staff who appeared in the dark about unfolding events.

“Tired. Exhausted. Frustrated. Yeah, you know, it’s just a mess, right?” Lisa Beraid, 48, who works for an insurance company, told AFP, as she waited for a flight Saturday morning at New York’s La Guardia airport.

More than 20,000 flights were impacted by the stoppage, and the effects were rippling across the industry, with more than 3,900 US flights already cancelled on Saturday and another 2,500 delayed, according to tracking website FlightAware.

US Transportation Secretary Sean Duffy sought to assure Americans it remains “safe to fly” but warned it would take time to resume normal service.

“Operations are slowly returning to normal this morning. Planes are pushing back, taxiing, and taking off, and it is safe to fly,” Duffy said on X on Saturday, 12 hours after the outage.

“You will continue to see some delays and cancellations as carriers reschedule flights and reposition aircraft/crews where they are needed most.”

It was only the second time such a ground stoppage had been issued in US airspace — which is among the busiest in the world — since the 9/11 attacks.

“No one expects the whole airline system to go down,” said 77-year-old traveller Steven Rathe, who was waiting to embark on a four-leg trip from New York to Albuquerque.

“We’re lucky it wasn’t longer. So they’re flying today and for that I’m grateful.”

The US Federal Aviation Administration (FAA) said in a statement: “We appreciate your continued patience as operations return to normal.”

Decades-old equipment

The ground stop not only plunged US air travel into chaos; it has raised serious concerns about the country’s ageing infrastructure.

Trump administration officials blamed decades-old equipment and said there was no evidence of foul play, although the outage highlighted the potential vulnerability of the system to cyberattacks.

“We use 1980s little copper lines. It’s an old system that went down, and went down everywhere. It got overloaded,” Duffy, the transportation secretary, told reporters late Friday, appealing for $50 billion in funds to upgrade and modernise the air traffic control system.

He also ruled out any connection with the outage that affected Microsoft this week, knocking email systems offline for millions of users, public services and businesses worldwide.

US lawmakers on Saturday called for investigations into what caused the massive disruption and whether the country is adequately secure from cyber criminality.

“No more kicking the can. If today proves anything, it’s that we need to update our air traffic control system & rebuild our airport infrastructure,” Republican Senator Eric Schmitt said on X.

President Donald Trump was uncharacteristically quiet about the outage, which had knock-on effects for international flights into the United States.

As of mid-morning Saturday, he had made no public statement about the ground stop.

Desperate for information

The nationwide halt had lasted around four hours and was lifted at 8:15pm Eastern Time (6:15 PKT Saturday).

During the outage, footage from airports showed gates full, with planes waiting on taxiways and passengers thronging concourses, desperate for information.

FAA officials reopened the airspace “after restoring full functionality” at air traffic control facilities, according to Duffy.

Tim Johnson, consumer director at the UK Civil Aviation Authority, said that while US flights have resumed, “there may be some follow-on disruption as airlines work to re-book affected passengers and get all services back to normal”.

A nationwide ground stop is highly unusual.

There was one such stop in January 2023 when a pilot notification system failed, but the only other national stop happened in the wake of the 9/11 attacks in September 2001, when no commercial aircraft flew for days.

Confusion and delays

US airspace is among the busiest in the world, and is ramping up to its most frenetic as the Thanksgiving holiday moves into view.

The stop sparked chaos and misery at airports around the country.

“We’re trying to debate whether or not we need to reschedule or drive or what, but if the whole country is stopped, that means the highways are going to be jammed too,” said Joseph Anderson, 72, who was trying to fly from Las Vegas to Oakland, California.

At New York’s LaGuardia Airport, Tiara Johnson said she had been trying to get to Orlando for a concert with a friend.

“They just keep delaying it…So it started out at 7:55. Then it went to 8:30, 9:30. Now it’s at 10:30. So we don’t know when it’s gonna leave,” she told AFP.

“I feel very frustrated because you know, you come to the airport and then all of a sudden your whole plans have changed and you don’t know when you’re leaving. We’re kind of stuck.”

Stranded passengers were scrambling to find alternatives, with long lines forming at rental car counters at the airport in Las Vegas.

Susan Sardina said she had boarded her flight back to Orange County, California, when staff told passengers there was a problem. “We were already on our flight to leave and we were told to get off,” she told AFP as she stood in a lengthy queue for a rental car.

For those looking on the bright side, the delay was a chance to extend a break.

Kathy Sommers was on her way home from visiting friends in Las Vegas when her flight got cancelled.

“We’re blessed that our friends are coming back to pick us up,” she said. “So one more night to play cards.”