Originally Posted by Paplover

Two reasons that this doesn't work. Currently DL does not allow any pets in the cargo holds. Many years ago they removed the option of traveling with pets as checked luggage and forced them to be transported as cargo. Since COVID there has been an embargo on accepting pets as cargo, except for military traveling on orders Shipping Pets (delta.com), so the only way to transport an animal on a DL flight is in cabin as a service animal or underseat in a carrier. Second, many underseat carriers are soft-side, made of fabric. For pet and airline personnel safety there are requirements for carriers placed in the cargo hold that they be hard sided, metal or strong plastic, and all openings secured so the animal cannot escape, usually ziptieing the door closed. Obviously, the in cabin carriers do not meet these safety requirements.