American Airlines tightens rules for support animals in-cabin
Emotional / psychiatric support and fully-trained service animals can fly in the cabin at no charge if they meet the requirements.
Animals must be able to fit at your feet, under your seat or in your lap (animals to be seated on lap must be smaller than a 2-year old child). For safety reasons, you won’t be able to sit in an exit row when traveling with your service or emotional / psychiatric support animal.