UPDATE 5-Some US airports back to normal after computer glitch

(Updates with some airports returning to normal operations)

WASHINGTON, Aug 26 (Reuters) - Air traffic at some major U.S. airports was returning to normal on Tuesday after many planes were delayed due to a glitch in the computer system for filing flight plans, the Federal Aviation Administration said.

The Department of Homeland Security said there was no link to terrorism and the FAA said the computer glitch did not affect its ability to safely track planes in the air.

An FAA official told reporters during a conference call that the agency hoped to have the problem resolved by around 6 p.m. (2200 GMT).

Flights from a wide swath of the United States, from Dallas and Chicago to the East Coast, had been delayed, according to the FAA.

“It looks like we’re slowly starting to dig out of this,” said Hank Krakowski, chief operations officer for the FAA’s air traffic division. FAA officials said they did not know how many flights had been delayed by the computer breakdown.

Krakowski said operations in New York were normal and delays in Boston were clearing up. He added that Baltimore’s airport was improving but still experiencing delays and Washington, D.C., airports were operating normally.

FAA officials said the most significant delays appeared to be continuing in Atlanta, which also was experiencing severe thunderstorms in the region that further hampered travel.

Flights out of Chicago’s O’Hare airport were experiencing delays of more than one hour, Krakowski said.

FAA spokeswoman Diane Spitalire said the agency had never experienced a computer problem this severe. “We’ve had some equipment failures but not like this,” she said.

The problem began at 1:25 p.m. (1725 GMT) when a communications link failed in the system that processes flight plans at a facility south of Atlanta, FAA officials said. The cause of the failure was not known but it was not due to a computer hacking attack, Krakowski said.

“It appears to be an internal software processing problem. We’re going to have to do some forensics on it,” he said.

Flight plans include information like the type of aircraft, destination and number of passengers.

The other flight-plan facility in Salt Lake City was now handling the entire country, FAA spokeswoman Tammy Jones said. An FAA official in Chicago said workers there were filing flight plans by hand.

International flights were being given priority, the FAA said.

American Airlines flights are facing delays in the Northeast "but not massively at this point," said Tim Smith, a spokesman for the airline's parent company, AMR Corp. AMR.N

An FAA communications outage in Memphis last year caused huge air-traffic snarls. The technicians’ union blamed FAA cost-cutting for reducing backup standards. (Additional reporting by Andy Sullivan, Diane Bartz and Randall Mikkelsen in Washington, Jim Loney in Miami, Kyle Peterson and Andrew Stern in Chicago, Karen Jacobs in Atlanta, Scott Malone in Boston and Anna Driver in Houston; editing by David Alexander and Mohammad Zargham)