Many people fly with their dogs and cats as support animals and some people are trying to bring goats, pigs, and several other types of animals. Unfortunately people are abusing the system because they do not want to pay to have their animal shipped. Which ruins it for those that truly do rely on their support animals because now the airlines are working to eliminate the abuse and this is making it more expensive for those truly in need.
This article is NOT the “Complete Guide” as it only discusses the major US Airlines. Best to call your airline directly and find out their policies on flying with animals.