I have not yet found any airline that will allow pets-in-cabin on flights from North America to South America.
There are (or at least used to be) several airlines that allowed pets in the cabin on flights to and from North America to Europe. So if you hear of pets being allowed on flights, be sure to ask what the destination was.
Some of the inexpensive (that's relative, isn't it?) airlines advertise that they allow pets in cargo, but on a hidden page in very small print, they state that they do not allow pets to travel in high season. So verify that your pet can fly before you purchase tickets.
You can probably get an service animal into the cabin, but you'd be hard pressed to explain how a 15 year old cat is a service animal.
Funny thing about dogs in the cabin. I've flown with dogs many times and no one ever notices. The only ones who notice the dog are very small children. Adults don't even notice that there is a dog in the carrier when walking through the airport or seated in the waiting area. It is against regulations to remove the pet from the carrier inside the plane.
As for allergies, the airlines don't consider it their problem. I'm allergic to strong perfume and tobacco smoke so I get to wheeze and cough my entire flight. Why should cat allergies get preferential treatment?
My preference is that pets be allowed and small, screaming, running, seat-kicking children be required to fly in the cargo hold.


