CHICAGO _ United Airlines said it expected "minimal impact" to Monday flights after a computer issue caused the airline to ground all domestic flights for 2 { hours Sunday night.
United said more than 200 flights were affected Sunday. On Monday, the airline said it planned to cancel a dozen flights, out of about 4,500 on its schedule, and expected a "small number" of short delays.
The problem affected the system the airline uses to send pilots information needed before flights can depart, such as weight and balance information, and there was no sign it was caused by a hack or security breach, the airline said.
It's the latest in a run of technology problems at major U.S. carriers.
Last summer, both Delta Air Lines and Southwest Airlines canceled more than 2,000 flights in separate information technology incidents that disrupted flights for days.
Airlines' information technology systems are particularly complicated, and more complex systems mean more ways for things to go wrong, said Mark Jaggers, an analyst at technology research firm Gartner.
Some of the systems airlines rely on were designed years ago, with numerous updates "bolted on" over time, and multiple points where a single problem can shut down operations, Jaggers said. Tighter flight schedules make it tougher to recover when things go wrong, meaning outages take a more visible toll, he added.
United's issue Sunday was comparatively minor. But "any technical failure that brings an airline to a complete stop for more than a moment or two affects a large number of flights and a larger number of people," said travel industry analyst Henry Harteveldt, founder of Atmosphere Research Group.
The system that halted United's planes, called Aircraft Communications Addressing and Reporting System, or ACARS, is used by a number of other airlines and hasn't caused problems before, Harteveldt said.
He credited United with addressing the issue quickly, even if that's little consolation for angry passengers who spent extra hours in transit.
"I think all airlines have realized they have to have a plan for software failure, and some do go through periodic exercises where they say, 'If this software went down, how do we recover?'" Harteveldt said.
Although United has had its share of information technology outages, in November, United said technology-related flight delays declined 57 percent in 2016 compared with 2015 and were at their lowest level since 2012.
