https://www.airlinespetpolicy.com/airlines/american-airlines-pet-policy.html

American Airlines allows dogs and cats to be transported as cargo on a first-come basis with American PetEmbark.  American Airlines pet policy is very pet friendly. Animals are permitted to travel in-cabin, as checked baggage, and as manifest unaccompanied cargo. Depending on the breed and size of the animal, it can travel as a carry-on or via American Airlines Cargo.