The benefits and popularity of frameless soft sided pet carriers is their pliability and ability to conform to varying seat configurations of modern aircraft. All airlines actually have similar sizing requirements, and those are more stringently applied to the older hard shell pet carriers. All airlines will require your pet to stow under the seat in front of you, and virtually all aircraft set their seats at 8.5" seat. Most of my models ( not the Rhodium ) are easily pliable to be able to accommodate your pet with maximum space but yet conform to fit under the 8.5" seat. Keep in mind, airline capable carriers are designed for your pet to be laying down, as most pets will need to do so to allow for fitting under the seat.