They'll give you a seat belt extender to belt the seat in. You do not have to use your base, but you'll want to gate check it if you plan on using it at your destination.
Her first flight she was a few months old. I followed others advice and fed on the way up and way down. She slept the entire time. However, she was an easy baby. We haven't taken #2 anywhere yet because she is the opposite! I also suggest bringing extra clothes for you just in case. And lots of extra diapers and wipes in case of delays or cancellations! (That happened to us once...)
We used our car seat on our flight from Hawaii back to kansas we got lucky though we didn't buy a seat they just had an open one... it was fantastic he slept pretty much the whole way, but I def. second what a previous poster said about bringing extra clothes for you I went through 2 shirts before I ever got on the plane. I lost one going through security because my under wire set off the metal detector and when I got searched the lady ripped my shirt, shirt number looked what had a loose string so I pulled it apparently it was the only string holding my tank top together so by the time I got to my seat I was on shirt 3 and it had nothing to do w/ DS
Re: Airplane travel with the Chicco Keyfit 30