American Airlines stopped flights heading to Dallas, Chicago and Miami on Thursday because of a computer-systems problem.
American spokesman Casey Norton said the airline did not immediately know the cause of the outage, which began around 11 a.m. CDT. He said crews were working to fix it.
The Federal Aviation Administration said that American Airlines planes destined for Dallas-Fort Worth International Airport, O'Hare Airport in Chicago and Miami International Airport were being held on the ground until midafternoon.
American did not immediately say how many flights were affected.
The outage comes at an awkward time for American Airline Group Inc., the world's biggest airline. In less than a month, the company plans to complete combining the reservations systems of American and its US Airways subsidiary and retiring the US Airways brand.
Combining technology systems is a difficult feat that has tripped up other airlines, notably leading to several outages at United Airlines after it merged with Continental Airlines in 2010. United suffered two major outages this summer.
American has made meticulous plans to avoid a similar fate. Among other moves, it will reduce flights to lighten the load on its network while it combines the two reservations systems.