If you plan ahead and are certain you can bring your Chihuahua on the plane, you must keep your dog in its crate for the entire flight. If your Chihuahua is not used to being in a crate, begin training your dog at least 2 months in advance. Keeping this in mind, think about how long the flight will be. If longer than 4 hours, you may wish to consider a lay over with plenty of time to bring your dog outside of the airport to stretch his legs and eliminate before boarding the next flight.