I just called American Airlines as we are traveling to Chicago this month with Ransom.
The lady in customer service on the phone advised that since I am only traveling domestic that I did not need a health certificate. I'm not sure I'm going to take her word so for "just in case" measures will still continue to take Ransom to his vet for his 10 day health certificate.
This lady was cute. I think we talked more about Yorkie's then actually booking him on his flight with us. Her daughter has a Yorkie and she says she's wild (the Yorkie) and that she is always hit up to babysit her daughter's Yorkie. LOL
I can't wait to travel with Ransom (Schatzie is staying with a friend) and feel fortunate that he wont need any "calming sedatives" before his flight. He's pretty much calm all the time.