American Airlines said Tuesday it had grounded all its aircraft due to problems with its reservation system.
"American's network system is experiencing intermittent outages," AA said on its website.
"We are on a system-wide ground delay that will last until 4:30 pm CST (2130 GMT) as we work to resolve this issue as quickly as we can," the company said, apologizing to customers for "any inconvenience."
In a Twitter message, AA said: "The issue is w/ our ability to access our res system & not w/@SabreNews. We apologize to Sabre & customers for confusion.
In an earlier tweet, AA had said "our reservation & booking tool Sabre is offline."