Computer issue caused airline chaos
United Airlines has said 580 flights were delayed because a piece of computer equipment failed to communicate correctly, and its back-up system did not work as expected.
The failure shut down United's website for more than two hours and prevented workers from boarding passengers on time.
The US carrier's passengers reported long lines in the airline's hubs in Newark (New Jersey), San Francisco, Houston, and Chicago. It also caused nine cancellations.
United Continental Holdings said that it is still working to find out why the computer equipment did not work properly on Tuesday.
The problems came on the same day that airlines already had to deal with Hurricane Isaac, which has disrupted travel in cities around the Gulf of Mexico.