I have the medium Sherpa on wheels. I have used it on express jet, Delta, United, and one other??? The security does not know about what each airline accepts. Some allow two, some do not. Security just wants to make sure you have only acceptable items. The flight attendents may know or be aware if there are suppose to be animals on a flight, so you may want to be careful about taking dogs on without prior arrangements. They can fine you more than what the dog's ticket would have cost or even refuse you to reboard on a multiflight trip.
I have not had any of the airlines check the bag size, most do not check the health papers unless I ask if they want to see them. |