According to Northwest spokesman Roman Blahoski, flights across the U.S. were affected.

Worldspan provides global electronic distribution of travel information, Internet products, and connectivity and e-commerce capabilities for travel agencies, travel service providers and corporations.

By midafternoon Tuesday, the system began gradually returning to normal, according to a statement e-mailed to Computerworld by Northwest. The problem caused delays averaging about 21 minutes for approximately 285 of Northwest's 1,364 daily scheduled flights, Blahoski said. Some Northwest Airlink flights were also delayed, and a few were cancelled outright.

Northwest expected to operate its full schedule Wednesday, and there were no cancellations related to the computer problem. As of 11:30 a.m. (Eastern Time), approximately 80 Northwest flights had been delayed by an average of 20 minutes, according to the airline.

Blahoski said the airline's IT department has not yet determined what caused the problem, but it has continued making progress in restoring the system to normal operations. In the interim, redundant systems and manual backup plans were used to minimize any impact on airline customers.