American Airlines has added the ability to make same-day flight changes online at aa.com. Now, beginning 24 hours before departure, you can request a same-day flight change through the online check-in page–this is a new, longer booking window, changed from 12 hours before departure.
You simply select each passenger in your reservation who is requesting a flight change, and pay the $75 per passenger change fee. The change in reservation must include the same origin and destination, be the same calendar day of departure and have seats available.
Passengers traveling on unrestricted Y fares and AAdvantage AAnytime travel awards can make flight changes at no charge. If you are traveling on a MileSAAver award, you can change the date/time of your flights at no charge, provided seats are available on the desired flight; if award seats are not available on the desired flight, you may obtain a confirmed seat on the same day by paying the $75 charge.
Customers who purchased a Choice Plus fare have the flexibility to change one flight at no charge, provided seats are available on the desired flight. Same-day flight changes are available for flights in the U.S., Puerto Rico, U.S. Virgin Islands, Canada and the Caribbean on American Airlines, American Eagle and AmericanConnection. You can continue to make a same-day flight change over the phone, at an airport kiosk or at the airport ticket counter.