And if you choose to purchase a seat for your baby in order to use your airline - approved car seat on board, flying with baby is expensive. (havebabywilltravel.com)
But managing car seats on board an airplane is a pain. (rookiemoms.com)
If you have paid for your child's seat you can take your regular car seat on board as long as it is FAA approved (if it's not, it will not be allowed). (sleeptrainmybaby.com)