To avoid the glitches that followed other airline mergers,
Once the 90-day transition is completed as early as October, the US Airways reservation system and website will disappear and all bookings will be converted to American Airline reservations, airline officials said.
The two airlines have already merged their loyalty rewards programs.
The merger of American Airlines and US Airways to form the world's largest carrier was announced in December 2013. Among the steps remaining to complete the merger is the union of several labor groups and the integration of the two flight operating systems.
In some previous airline mergers, reservation systems and loyalty reward programs were transferred from one airline to another in an overnight process known as the "knife's edge," said Maya Leibman, American's chief information officer.
United Airlines suffered several computer crashes after transferring its reservations to the system of its merging partner Continental Airlines.
Instead of an abrupt transfer, American Airlines said it would use a "drain down" approach starting in July.
If the reservation system transfer is a success, Leibman said travelers on either airline won't run into any problems.
"Our focus is to make this seamless," she said.