A five-hour computer outage virtually shut down United Airlines on Friday night and early Saturday.Passengers saw their flight information vanish from airport screens, and thousands were stranded as United canceled 31 flights and delayed 105 worldwide. The airline still had no explanation Saturday afternoon for the computer problem.United spokesman Charles Hobart said Saturday that the airline didn’t expect to cancel any more flights this weekend because of the computer problems, though delays might continue.

The airline could not say how many passengers’ travel plans were affected. United was letting people with tickets for travel Saturday change them for free to alleviate any backlog of passengers caused by the computer problems.Friday’s shutdown occurred late enough in the day that many of the canceled flights were the last planes out for the day, said Henry Harteveldt, an airline analyst with Forrester Research.On a typical day, United, a subsidiary of United Continental Holdings Inc., cancels 15 to 30 flights for reasons ranging from fog to maintenance problems or staffing shortages.