Naio wrote:
Planes do require a note from the person's doctor, but not training certificates.
That's because airlines allow "emotional support animals" to ride in the passenger compartment. This is different from a "service animal," which is trained to perform tasks on behalf of a disabled person--those are permitted to go anywhere the person goes, including restaurants and grocery stores (think guide dogs for the blind).
Most people don't realize there's a difference, and that's why you see people in stores with animals that clearly aren't trained to perform tasks on behalf of a disabled person, and therefore aren't service animals. There's no law that requires that they be allowed (and in fact there are laws say they
aren't allowed in places that prepare food), but the pet owner is relying on people's ignorance about what the law is, and businesses are scared of being sued if they tell someone they can't bring in their pet.