ATLANTA/WASHINGTON (Reuters) – A computer problem with a flight-processing system disrupted United States airline travel on Thursday, with the heavily trafficked New York area hit particularly hard through cancellations and delays.

The Federal Aviation Administration (FAA) said a software problem with the agency’s telecommunications network prevented controllers from electronically managing flight plan data.

Information was processed manually, slowing ground traffic. Controllers also limited airborne traffic as a precaution, allowing fewer planes to take off.

Radar for tracking planes in the air was not affected and there were no safety problems, the FAA said in a statement.

The matter was under investigation.

The four-hour outage struck just before the East Coast early morning rush and was fixed by 9 a.m. Eastern Standard Time (10 p.m. in Manila). Flight disruptions extended into the afternoon.

The problem affecting thousands of passengers came less than a week before the heavily traveled  Thanksgiving holiday period and renewed focus on the durability of the aging air traffic system.

Many of those impacted on Thursday were business travelers.

“This is an unacceptable drag on corporate productivity at a time when we need the government to be the best partner of a private sector trying to drive economic growth,” said Michael McCormick, executive director of the National Business Travel Association.

The disruption followed a similar incident in August 2008 that also delayed and canceled flights.

Arrival delays exceeding one hour lingered at New York-area airports into the evening with rain compounding the problem. Philadelphia reported delays of more than two hours. Flights into Atlanta and Chicago ran with few delays by afternoon.

All big US airlines were affected. Atlanta-based Delta Air Lines reported delays and cancellations into the afternoon, saying operations were returning to normal slowly. Delta did not provide figures for disrupted flights.

AirTran Airways, a unit of AirTran Holdings based in Orlando, Florida, said 38 flights were canceled and dozens more were delayed nationwide.

US Airways reported 75 delays of its mainline fleet averaging 30 minutes. The Philadelphia airport, where US Airways operates a hub, reported delays for all carriers exceeding two hours in some cases extending into evening. US Airways did not report delay data for its express units.

Continental Airlines reported morning delays averaging one hour, primarily at hubs that include Newark. American Airlines, a unit of AMR Corp, said delays in its network were minimal.