The FAA grounded every departure.

WASHINGTON — The Federal Aviation Administration ordered every departing flight in the country to stay on the ground Friday afternoon. The stop was in force with no time given for when it would lift. The New York Times, USA Today and NBC News reported the order.

The agency’s advisory said “all airports are ground stopped,” for “extraordinary circumstances and for reasons of safety.” “All departing traffic should remain ground stopped until further notice,” it said. Landings of inbound international flights were to be handled case by case. Reuters reported that the notice went out at 3:54 p.m. Eastern. USA Today reported that the advisory listed an end of 11:30 p.m. Eastern, and that the listed hour did not mean departures would start again.

This isn’t another 9/11.

Sean Duffy, the transportation secretary, wrote on X that the stop followed “a communication issue impacting all Air Route Traffic Control Centers.” “FAA technicians are investigating the issue,” he wrote. “We will provide immediate updates as we have them.”

Markwayne Mullin, the homeland security secretary, spoke to reporters outside the White House. “This isn’t another 9/11,” he said. “I just can’t repeat that enough.” He said: “This is a telecommunication outage.” He said: “There is no indication, and we had no reason to believe as of right now that this was a threat to the United States.” He said the flights had been grounded “out of abundant caution,” and that “all the flights are accounted for.” He also said: “There was no indication as of yet that this was a nefarious attack against us. It’s just a telecommunication outage as of right now.” Asked if officials knew the cause, he said: “No, we’re going to go through it. But I’m not going to make assumptions.” The Times reported that he said a fix would “take some time.”

The count climbed through the evening. The Times, citing FlightAware, reported more than 7,800 delayed flights and about 350 cancellations as of about 4:45 p.m. By 6 p.m. Eastern the same tracker showed more than 10,000 flights delayed and 1,700 canceled. Just after 6:30 p.m., the Times reported, cancellations had passed 3,000, and more than 370 Saturday flights were already off the board. By 6 p.m. about 600 flights had been diverted, most of them back to the airport they had left. O’Hare had 28. Denver had 26. Those figures are the Times’s, taken at those hours. They are not added together.

At O’Hare, passengers sat on the floor and on their phones. Frank Foto, 34, told the Times he feared his family would miss a cruise from Miami. Ashley Van Mills, 45, told the Times at Atlanta that she had never seen a stop like it. Jack Healy of the Times wrote that he had spent two hours on a United jet at O’Hare, bound for Rochester, New York, after the stop caught the flight at the runway.

The Times said the stop had already lasted longer than the last nationwide ground stop, on the morning of Jan. 11, 2023, which ran about 90 minutes after a system that warns pilots failed. Before that, the last nationwide stop followed the attacks of Sept. 11, 2001. Delta told the Times that no Delta flight was leaving, and that planes already in the air would continue. At 6:55 p.m. the Times reported that the FAA had asked Eurocontrol to hold flights to the United States from 42 European countries. Mexico’s aviation agency said the FAA had asked that planes in Mexico bound for the United States stay on the ground.

A spokeswoman for Northern Command and NORAD told the Times there was no evidence yet that the outage was a nefarious act by anyone at home or abroad. Senator Tammy Duckworth said: “I’ll be demanding answers from the FAA.” NBC News reported the same account Mullin gave at the White House: no indication yet of a nefarious act, and, as of then, a telecommunications outage.