ATLANTA (AP) — Air travelers nationwide scrambled to revise their plans Thursday after an FAA computer glitch caused widespread cancellations and delays for the second time in 15 months.

The Federal Aviation Administration said the problem, which lasted about five hours, was fixed around 10 a.m., but it was unclear how long flights would be affected.

Doug Church, a spokesman for the National Air Traffic Controllers Union, said controllers were still entering flight plans manually in some locations even after the glitch was fixed.

Aviation officials told The Associated Press that the problem began at the computer center in Salt Lake City. The officials asked not to be named because they were not authorized to speak publicly.

FAA spokesman Paul Takemoto said the problem started between 5:15 and 5:30 a.m. Airplane dispatchers had to send plans to controllers, who entered them into computers by hand.

"It's slowing everything down," Takemoto said.

Hartsfield-Jackson Atlanta International Airport, the world's busiest, was particularly affected. The problem was exacerbating delays caused by bad weather in the Northeast, with airports in the Chicago, Washington, D.C., and New York metro areas reporting problems.

Some flights were more than two hours behind schedule. Airports around the South also reported delays and cancellations.

U.S. Sen. Charles Schumer, D-New York, said the country's aviation system is "in shambles" and the FAAneeds more resources to prevent such problems from continuing.

"If we don?t deliver the resources, manpower, and technology the FAA it needs to upgrade the system, these technical glitches that cause cascading delays and chaos across the country are going to become a very regular occurrence," he said in a statement.

In Atlanta, sisters Sharon Walker and Sheila James were taking their elderly mother, Rosa Washington, to see their other sister in St. Louis. The trio's 9:30 a.m. flight out of Hartsfield-Jackson was delayed until 4 p.m.

"We were going to be there for a four-day weekend, but now it's getting cut short," James said as she sat with her family in airport atrium. "It's just not a good day."

AirTran canceled at least 22 flights and delayed dozens more. Delta Air Lines was also affected. American Airlines spokesman Tim Smith said several hundred flights would be delayed around the country. He said American was told the problem would be fixed soon, "but once you get behind, it tends to stay that way" throughout the day.

Julie King, a spokeswoman for Continental Airlines, said delays averaged about an hour from 6 a.m. to 8 a.m. and were concentrated at the carrier's hubs in Houston, Cleveland and Newark, N.J.

Passengers were asked to check the status of their flights online before going to airports.

At Dulles International Airport in Chantilly, Va., nearly all departures were still on time. But passengers on AirTran flight 63 to Atlanta were trying to make other arrangements after that flight was canceled.

Hilda Ruffin of Manassas said the airline urged passengers to head to nearby Reagan National Airport to catch another flight to Atlanta. But for Ruffin, a senior citizen who uses a wheelchair, that proved difficult. She eventually lobbied the airline for a free shuttle pass to Reagan.

"I really fought for it...I don't have the money to pay for a cab," said Ruffin, who was trying to get to San Antonio.

Houston's two airports and Dallas-Fort Worth International Airport reported few delays but said things could get worse, especially for travelers headed east. Los Angeles International Airport also reported that delays were likely later in the day.

The problem hinged on flight plans collected by the FAA for traffic nationwide at two centers — one in Salt Lake City and the other in the Atlanta area.

Victor Santore, the National Air Traffic Controllers Union southern region vice president, said he began getting e-mail messages from air traffic controllers around 7 a.m. EST Thursday that the Atlanta-area computers had stopped processing plans.

Santore said some controllers were pulled away from their normal duties talking to airplanes or pulled off breaks to help enter the flight plans.

"When something crazy like this happens, we'll pull everybody onto the floor," Santore said. "Every airport at some point some will be affected ... (The delays) are going to ripple through the entire system."

In August 2008, a software malfunction delayed hundreds of flights around the country.

In that episode, the Northeast was hardest hit by the delays because of a glitch at the Hampton, Ga., facility that processes flight plans for the eastern half of the U.S.

The FAA said at that time the source of the computer software malfunction was a "packet switch" that "failed due to a database mismatch."