If you are bringing your dog into the cabin on the plane, they are expected to be in a secure carrier and tucked under the seat in front of you. If you purchase a separate seat and ticket for your dog, you will be allowed to keep your dog and carrier on the seat. Most airlines require carriers to be certain dimensions or that dogs be under 20 pounds to fly in the cabin. For airlines that do offer cargo transportation for larger canines, dogs will be put in the cargo area of the plane. The cargo area is located in the belly of the aircraft.