My advise is - better safe than sorry- if the child has its own seat in the plane- use the car seat on the plane- it is the safest way for the child to ride- if not- airlines will put the car seat in a huge plastic bag and check it as luggage- then- you won't have to pay $70.00 or more-to rent one- from a car rental agency, you have one that you know fits the child- and you have it with you. I raised my kids prior to car seats- so not an issue when we traveled - but when our grandson was young- my daughter always hauled it with her- and there was never a worry. Might have been more work- but worth the peace of mind. rlb