UPDATE: (CNN) -- American Airlines' computer systems are back online, but the carrier expects more flight delays and cancelations for the rest of Tuesday, American Airlines said in a written statement.
American Airlines has instituted a "system-wide ground delay" until 5 p.m. ET, the airline tweeted Tuesday.
Earlier, the airline reported a problem with its reservation and booking tool, noting the network was experiencing "intermittent outages."
American estimates it flies about 275,000 passengers a day and receives more than 239,000 reservations calls.
CNN's Devon Sayers contributed to this report.