It could take several days for thousands of stranded travelers to get home after a United Airlines computer system shut down for several hours, leading to widespread cancelations Friday night.
The unspecified "network connectivity" problem was fixed and flights resumed early Saturday, but the airline said delays could persist throughout the weekend. Also, with flights nearly full, there was little room for passengers whose flights had been cancelled to rebook.
"There's literally nowhere to put them," airline analyst Robert Mann said. "There are already very few empty seats on the flights that operate."
United's planes were an average of 86.8 percent full in May.
To try to alleviate the congestion, the airline allowed passengers with tickets on Saturday flights to cancel or delay their travel to a later date without charge. Luckily, Saturday is one of the lighter travel days.
The outage started about 7:15 p.m. CDT Friday and lasted for about five hours. Long lines of passengers formed at airports in San Francisco, Los Angeles, Denver and Chicago. Some passengers ended up spending the night at airports or found hotel rooms in the cities where they were stranded.
United said its flight departures, airport processing and reservation system, including its website, were affected by the outage.
Some Continental Airlines passengers also were affected by the outage.
United and Continental merged in May 2010. They still operate as separate airlines but are slowly integrating systems. United spokesman Charles Hobart said Saturday morning that Continental was able to dispatch flights normally, but some of its airport kiosks were affected. He would not comment on the total number of cancelations or passengers affected, saying the airline was still updating its information.
Airlines today place greater reliance on computers than a decade ago. Most passengers are now asked to check-in online, at airport kiosks or via their mobile phones. When the system crashes, the problems are just that much greater.
"They're infrequent, but the fact that they happen at all is puzzling. These are mission critical," Mann said. "The idea that they would fail is troubling."
While the airlines have sleek, modern check-in kiosks at the airports, the underlying reservation system behind them dates back to the 1980s, Mann said. Many airlines that went through bankruptcies in the past decade, including United, didn't invest in new systems.
When the system fails, flight plans and dispatch operations must all be done on paper.
"There are fewer and fewer people at airlines who are familiar with or able to operate with a manual system," Mann said.