American Airlines tweeted a notice earlier today alerting customers that its booking and reservation tool was unavailable.
Our reservation & booking tool Sabre is offline. We're working to resolve as quickly as we can. We apologize for any inconvenience.
— American Airlines (@AmericanAir) April 16, 2013
According to CNBC, the outage is interrupting passenger check-in and causing flights to be delayed across the country. United Airlines ran into a similar issue back in August, blaming the outage on a piece of hardware. United grounded planes across the country, affecting nearly 200 flights.
Check back for updates.