My sister flew with her cat all the way from Los Angeles to Boston, complete with one layover, when she moved. Some tips.
1. Get an airline approved cat carrier that can fit under the seat (different airlines have different under the seat heights). She got this carrier
Amazon product ASIN B002N7X7S0and these pads to line it with (one to have in under the fleece pad that came with the carrier, one to have as a spare)
Amazon product ASIN B0046GFB58The carrier may seem pricey, but it is superb quality, and it really helps having a top load option, plus all the window options. The top can be squished down a little, so it works perfect for under the seat. It looks large, but fits under the seat well. Her cat is the brother of the one cat I have in my avatar, he is about double her size, so we wanted the largest carrier possible.
2. Once you decide on an airline (I'll post the one she went through, I can't remember right now), make sure you read all the rules and requirements for traveling with a pet. Some allow only 1 or 2 in-cabin or x number of pets per flight, so make sure you call and speak with someone to make certain he will be allowed and you know all the rules.
EDIT: She flew with American
3. Go to his vet and get him updated on vaccines if he isn't already (rabies is the main one) and get a health certificate from the vet (you go to the vet, say your cat is flying in cabin with you from destination A and B, fill out some forms, and they give you a certificate)
4. Get a harness and leash. At the airport, you *WILL* have to take your cat out of the carrier to walk through the TSA screening so the carrier can go through the x ray. If your cat is very skittish and you feel uncomfortable taking him out there, you can request to be screened in a private, closed room. This is what my sister did, as she didn't want to stress him out more than necessary and going in a small room is more like a vet visit so not as scary. She got this harness and leash set
Amazon product ASIN B000OBH1Q6
5. If you have used it before, or want to try it before the trip to see if it helps, getting a kitty pheromone spray like Feliway or nature's rescue remedy or something similar, that might help. A lot of people rave about how the products work really well
6. A lot of vets are hesitant to prescribe tranquilizers, since they can affect the kitties breathing or causes they opposite reaction. If your kitty does okay traveling in the car to the vet, then I wouldn't tranquilize him. If he doesn't then I would do a test run of the tranquilizer to see how he reacts with it.
7. Do not fly with an airline that will not let your kitty fly in-cabin with you. Flying in cargo is dangerous, and more stressful for animals. People's animals have died or got lost and ever found, so it's not worth the risk in my opinion when most airlines will allow a cat in-cabin under the seat.
8. He probably will meow in the airplane, but it's not a big deal. My sister's cat meowed a lot at first, but then quieted down and was silent the rest of the ride.
9. There can be a draft under-the-seat, so make sure to bring a blanket or extra jacket to wrap around the carrier if it is entirely exposed or it gets really chilly.
10. Do not, under any circumstance, open the carrier to pet or comfort your cat or take him out unless you are in a secure and enclosed room (ie not the airplane or airport)
11. Make the airport carrier a happy place, ideally not the same used to take the kitty to the vet or unpleasant places. Leave it on the ground open, throw some treats and toys in there, and let your cat get used to it for about a month or so if possible (Warning, after the trip, the kitty will most likely have disdain for the carrier for at least a couple months, at least her cat did)
He meowed and fussed a bit, but he did a great job overall! I'm just so proud of him. Thank you guys for all of the support 😍
