Hundreds of United Airlines flights were delayed Wednesday after the airline experienced computer problems for the second time in just over a month.
A White House spokesman said President Barack Obama was briefed on the glitch and that it appeared unrelated to an outage hours later at the New York Stock Exchange.
"There is no indication at this point either that there is malicious activity involved," said the spokesman, Josh Earnest.
A United spokeswoman said that the glitch was caused by an internal technology issue and not an outside threat or hacker.
Spokeswoman Jennifer Dohm said that a router problem reduced "network connectivity" for several software applications. "We fixed the router issue, which is enabling us to restore normal functions," she said around midday.
The Federal Aviation Administration lifted a ground-stop order after nearly two hours, allowing United planes to fly again Wednesday morning. But delays continued while the airline fought to regain control of its schedule.
United, the nation's second-biggest airline, said more than 1,150 flights had been delayed and about 60 canceled by late afternoon.
United has had three chief information officers since 2011, with the current CIO joining last September. It has suffered several technology lapses in that time, some leading to mass delays and cancellations.
The airline briefly halted all takeoffs in the U.S. on June 2 because of a problem in its flight-dispatching system. United said then that about 150 flights were affected.
United also struggled through a series of computer outages in 2012 after switching to the passenger-information system of Continental Airlines after that carrier merged with United. Those outages caused hundreds of flights to be delayed. High-paying business travelers were outraged; United CEO Jeff Smisek apologized for failing to provide good customer service.
After a 2010 merger, United elected to combine many computer systems and frequent-flier programs all at once. Executives believed that any disruptions would thus be short-lived. By contrast, Delta and Northwest integrated their systems in stages after a 2008 merger, and American Airlines is taking Delta's same go-slow approach now as it absorbs US Airways.
Other airlines, however, have also been hit by computer problems. In April, more than 50 American flights were delayed when a software glitch prevented pilots from seeing some airport maps on their tablet computers.
After Wednesday's problems, United apologized to customers and said they could change travel plans without being charged the usual $200 reservation-change fee. In some cases, the airline said it would also waive any difference in fare for the rescheduled trip.
At Los Angeles International Airport, Meni Tsirbas arrived an hour early for his morning flight to Newark, New Jersey. There was already a mob around the ticketing counter, and plenty of confusion.
"Everything was done by hand," said Tsirbas, an animation director. "We checked one (bag) and it was done '70s style."
Betsy Fischer Martin's flight to Denver sat on the ground at Dulles Airport near Washington as the captain gave increasingly dismal updates on the delay.
At one point, "The captain said, "Anyone who wants to look at the cockpit and flight deck is welcome—we have nothing better to do,'" said Fischer Martin, a journalist. "He made a bad situation a little better."
Gary Leff, co-founder of frequent-flier website MilePoint, said the breakdown "underscores the sense that something is very wrong at United."
"How could a router bring down one of the world's largest airlines?" asked Henry Harteveldt, a travel analyst at Atmosphere Research Group, who said it appeared that United lacked enough redundancy in its technology systems. Still, he doubted that United would lose many business-travel customers because technology hiccups could happen to any carrier.
Shares of Chicago-based United Continental Holdings Inc. fell $1.49, or 2.7 percent, to close at $52.82.
Explore further: Computer glitch disrupts US flights