Karoun DemirjianNiraj Chokshi and Hari Raj

Travelers across the United States and beyond were still facing delays and uncertainty on Saturday as airlines and airports sought to recover from the ground stop the day before that brought air travel to a halt for hours.

Thousands of passengers were stranded on Friday after the Federal Aviation Administration ordered the ground stop. More than 8,200 flights — or over 31 percent of those scheduled for Friday — were canceled nationwide, according to Cirium, an aviation data firm, though some international flights received permission to take off.

Sean Duffy, the transportation secretary, said at a news conference on Friday night that the authorities had decided to issue the ground stop after aging air traffic communications equipment became overloaded and began to falter on Friday afternoon.

He said that it would take “some time” for airlines to recover, predicting that flight schedules would return to normal in time for the busy Thanksgiving travel season.

Many who waited at airports until late Friday night had to scramble to find accommodation after their flights were canceled. Some carriers, including United Airlines and American Airlines, began to restore flights after flight traffic was restored on Friday night. Aviation experts have said it could take days to fully restore flight schedules after a halt of this scale.

Homeland Security Secretary Markwayne Mullin, who appeared alongside Mr. Duffy at the news conference on Friday, said there was no indication that the communications failures had been caused by a cyberattack, though he said that an investigation was underway and that he could not rule out such an attack. He stressed that lives were never in danger.

Mr. Duffy blamed lawmakers for not fully funding upgrades that he said were needed to prevent similar failures. To upgrade aging air traffic facilities and technology, he said, he wanted another $50 billion from the Republican-controlled Congress, which last year approved $12.5 billion for the project.

He said the new amount should be delivered in emergency funding by the end of the year, before control of Congress — and the budget — switches to Democrats.

If your flight is canceled: You are entitled to a refund if your flight is canceled in the United States, regardless of the reason, or if a flight is significantly delayed or changed and you decide not to take it. Here are other travel tips that might be helpful. Read more ›

Handling the chaos: Radio transmissions between air traffic controllers and pilots at major airports offered a peek at how they navigated the ground stop. Read more ›

Rare halt: Friday’s nationwide ground stop was only the third that the F.A.A. has issued this century. It ranks as the second-longest, after the stop issued in the wake of the terrorist attacks on Sept. 11, 2001. There was a shorter one on Jan. 11, 2023, because of an outage in the F.A.A.’s safety-alert system. Read more ›

Democrats’ response: Representative Hakeem Jeffries of New York, the House’s top-ranking Democrat, said the stop was “the latest in a series of unacceptable air travel incidents” under the Trump administration. He added that Americans deserved timely answers about how and why it happened.

Early Saturday, the aftermath of the ground stop still appeared to be rippling internationally. The departures board at London Heathrow Airport — Europe’s busiest hub and the largest gateway for flights between Europe and the United States — showed that a few dozen trans-Atlantic flights had been delayed or canceled. Around 5 a.m.

Eastern time, 19 flights between Heathrow and the U.S. had been canceled, and 22 delayed, according to the flight-tracking service FlightAware.

At Los Angeles International Airport, a number of travelers who had been hoping to get a late flight out have now been notified that their flights have been canceled. Many travelers here are scrambling to find new flights for Saturday as well as accommodation for the night.

Their flight to Jacksonville cancelled, longtime friends Ann Bruns, 79, and Janice Simpson, 78, opted to hire a driver to shuttle them six hours from Atlanta to Florida, where they hope to catch a cruise ship departing on Sunday.

“We’re about to go on a cruise ship with no clothes,” Simpson explained, because their luggage had already been loaded onto a plane bound for Jacksonville.

Bruns described a day punctuated by confusion, saying when the duo arrived in Atlanta from Kansas City, “We saw pilots just standing there, and we knew something was up.” They still feel like they have almost no idea what went wrong to send air travel into turmoil.

Nationwide, more than 8,200 flights — or over 31 percent of those scheduled in the United States for Friday — were canceled, according to Cirium, an aviation data firm. And the disruption was already spilling over into Saturday, usually a slower day for travel, with more than 5 percent of flights canceled before the day had even begun.

Reporting from Denver, where they are stranded along with much of the Democratic Party.

Pete Buttigieg could not believe what he had just watched. The former transportation secretary stood at the corner of the hotel bar in Denver, where CNN had just finished broadcasting the Trump administration’s news conference about the ground stop that stopped flights nationwide on Friday.

Mr. Buttigieg was among the thousands of Democrats who had gathered in Denver this week for a…