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At La Guardia Airport in New York on Friday, Divneet Wadhwa, 26, was stewing. Her flight to Toronto, where she was going for a wedding, had been delayed three times.
“I don’t think we’re going anywhere,’’ Ms. Wadhwa said, adding that she had events later and that being stuck in New York would “really mess everything up.”
She was just one of thousands of travelers across the Northeastern United States whose plans were upended Friday morning after a shortage of air traffic controllers triggered significant flight delays.
A few hours later, President Trump announced a deal to temporarily reopen the government, easing the increasing strain on federal agencies, for a few weeks at least.
The threat of disruption to the nation’s air-travel system had ratcheted up the pressure on political leaders, who feared a chaotic situation that would anger many more people than the 800,000 unpaid government workers.
Aviation industry workers and travel groups celebrated the breakthrough, but worried that it might not last long.
[In a surprise retreat, President Trump agreed to reopen the government for three weeks.]
“People are looking forward to getting paid and hoping for the best,” said Mitch Narzem, a controller who had just finished a 10-hour shift in Fort Worth, Tex. “Getting paid will alleviate some headaches, but it is just a three-week temporary thing and who knows?”
Mr. Narzem, 53, said that going unpaid for a month had been an extra burden on controllers.
“When you’re working a lot of airplanes, you need to pay attention and your mind doesn’t need to wonder about other things,” he said.
Paul Rinaldi, president of the National Air Traffic Controllers Association, the controllers’ union, expressed relief about the agreement, but called for an end to a funding process that produces shutdowns.
“The constant funding crises that arise from stop-and-go funding continue to wreak havoc on our system and perpetuate the current staffing crisis, which has resulted in a 30-year low of certified professional controllers,” he said in a statement.
Nicholas E. Calio, president and chief executive of Airlines for America, said the industry was grateful to the elected officials, but added, “As we have seen over the past 35 days, the pressures and strains of a shutdown are not sustainable; the disruptions to passengers, commerce and the economy are not tolerable. We urge elected leaders to continue working together to identify a solution that will keep the government open beyond February 15 and will continue paying the dedicated federal employees.”
The delays on Friday cascaded along the Eastern Seaboard, reaching as far north as Boston. As the F.A.A. rerouted flights and slowed air traffic, passengers saw delays of up to two hours at La Guardia, which was closed off to inbound flights until late morning. The delays began to clear around midday.
The F.A.A. blamed the trouble on a slight increase in the number of controllers calling in sick at two of its air-traffic control facilities on the East Coast, one near Washington and another near Jacksonville, Fla. Those facilities manage air traffic at high altitudes; some flights between the Northeast and Florida that normally would pass over the Atlantic Ocean had to take a wide detour over land.
The disruption came on the day the controllers and other federal workers missed a second paycheck. Many are on furlough, but the controllers, who are responsible for keeping planes from colliding, had been ordered to keep working because they are considered essential.
On Wednesday, the controllers’ union and other labor groups warned that the prolonged shutdown had caused the “air safety environment” to “deteriorate by the day.” But on Friday, the controllers union said in a statement that it had not organized and would not condone a coordinated sickout by its members.
“This is not a widespread use of sick leave, rather a symptom of how critically staffed our largest facilities are,” the statement said.
The Port Authority of New York and New Jersey, which operates La Guardia, as well as Kennedy International and Newark Liberty International airports, said 47 flights were canceled at La Guardia and there were 580 delays, which represented about half of the day’s flights. At Newark Liberty, at least 40 flights were canceled and nearly 300 were delayed; Kennedy did not have any cancellations, but there were more than 230 delays.
Delta said about 200 of its flights were delayed at La Guardia and other airports in the Northeast. The delays frustrated many travelers, including Valerie Pacheco, 34, who flew into La Guardia from Miami on Friday morning.
Ms. Pacheco’s friend was stuck in Vermont, she said. Instead of arriving at 10 a.m., the friend was due in at 1 p.m. — or later.
“I guess I’ll just have to sit here another two or three hours,” Ms. Pacheco said. “What I’m worried about is that they’ll cancel her flight altogether. Then we have a problem.”
The two had planned a “best friend’s weekend” in New York. “We were here to enjoy the city, and all that,” she said. “Now we’re getting a late start.”
Ms. Pacheco, who works in television production, said she feared that “we’re leaving our airports wide open for anything with this shutdown.” She added, “This is directly impacting us right now.”
The shortage of controllers caused some airlines to reroute flights. Peter Beadle was on a plane at Kennedy that was bound for Fort Lauderdale, Fla. After leaving the gate on time, the pilot announced that instead of flying over water, the plane would take a less direct path over West Virginia, Mr. Beadle said. That route would require additional fuel, so the plane had to return to the terminal.
“The pilot was apologetic, saying he’d never experienced this before and again confirming this was due to a staffing shortage of air traffic controllers,” Mr. Beadle said in an email. The pilot also explained that the controllers were doubling the distance between planes, further slowing traffic. The flight, which had been scheduled to arrive at 11:39 a.m., arrived more than two hours late.
The facilities that were short-staffed Friday are among about two dozen Air Route Traffic Control Centers, an official of the controllers union said. Each center controls a region, divided into several areas and monitored by dozens of controllers. They direct planes at high altitudes after receiving handoffs from local controllers.
The flight from Kennedy to Fort Lauderdale would normally have been guided by a center near New York City, then the one near Washington and, eventually, the one near Jacksonville, the official explained.
Union officials said the action the F.A.A. took Friday was highly unusual absent a severe weather event like a hurricane. Normally, they said, support staff would develop a plan to reroute traffic so that it would have minimal effects on flight schedules. But that did not happen, they said, because many of the people who provide that help to the controllers were furloughed because of the shutdown.