Airline and federal officials continued working to restore normal traffic on the East Coast on Sunday, a day after a routing-system glitch in a Washington-area control center caused hundreds of flights to be delayed or canceled.

The Federal Aviation Administration said in a written statement that officials were still trying to determine the cause of the outage of an automated routing system at a Leesburg, Va., control center that disrupted the management of 160,000 miles of airspace and forced the delay or cancellation of nearly 1,000 flights. The problem stranded passengers at Reagan National Airport, Baltimore-Washington International Marshall Airport and, to a lesser extent, Dulles International Airport.

Although the airports resumed normal operations by late Sunday, according to officials at BWI, Reagan and Dulles, it wasn’t clear how many passengers might still be trying to reach their destinations as the airlines worked through the backlog.

United had only a few residual delays on Sunday and kept disruptions to a minimum on Saturday, airline spokesman Rahsaan Johnson said. More than 97 percent of United’s flights took off and more than 75 percent arrived on schedule, he said.

Saturday’s malfunction caused the delay of 492 flights and the cancellation of 476 flights, the FAA said. As the FAA reduced arrival and departure rates from 11 a.m. to 4 p.m. for safety reasons, traffic fell to about 70 percent of the average at BWI, 72 percent at National, and 88 percent at Dulles. The agency said the routing system was restored to service about 4 p.m. Saturday. Federal authorities also said there was no indication that the system had been hacked.

On Sunday, one online site that tracks air travel reported that Dulles was still encountering two-hour delays. The FAA said it expected to resolve traffic-management issues by 4 p.m.

As aviation officials worked Saturday to shift the usual control of flight-routing around the Washington area, angry travelers took to social media, where the malfunction was dubbed “Flypocalypse.” Many complained that the FAA had kept them in the dark, posting nothing on Twitter, for example, until after the problem had been fixed. The FAA also said it was up to the airlines to sort out the scheduling after that.

Many people, including Noah Roehl and Maggie Wilcox, had little choice but to hunker down, perhaps for a day or more.

Roehl and Wilcox got up at 5 a.m. Saturday to drive from North Carolina to National Airport for a 4:40 p.m. flight to Denver after a week of vacationing. When the system shut down, they thought about taking a bus to New York and paying for a new flight.

Lucky for Roehl and Wilcox, they had a friend who could take them in for the night; the airline wasn’t paying for hotel rooms because it wasn’t its mistake, Roehl said. Despite the inconvenience, Roehl didn’t blame the airline, saying its staff was good about updating information.

“It’s really not their fault at all,” he said. “And it’s a safety issue.”

For Jeanean Willis Marsh, Saturday was a very expensive day, she said. Originally flying out of East Lansing, Mich., Marsh, 51, was supposed to land at BWI before 10 a.m., she said. Her flight ended up rerouting to Pittsburgh then landing at National about 4:30 p.m., meaning she missed a full day of hiking.

Marsh then had to rent a car to get back to BWI and pick up her vehicle.

“I’m just thankful to be home,” she said. “It’s been a long day.”

Although the malfunction caused delays and cancellations up and down the Eastern ­Seaboard, the problem was ­confined to the Washington air-traffic control center in Leesburg. That facility and others oversee flight routing once airplanes reach an altitude above about 20,000 feet. Below that altitude, they are guided by controllers at Terminal Radar Approach Control Facilities, known as TRACONs. Control towers at airports direct the flights on takeoffs and final approaches for landings.

But when the Leesburg control center encountered trouble, it could no longer route traffic at cruising altitudes. So the FAA and the airlines instead kept some flights below 20,000 feet and then coordinated their management between different TRACON controllers.

Will Greenberg contributed to this report.