We have traveled with Riley quite a bit in her first year- although yours is a little older.
Our last trip was over the holidays, and she was so great. The flights were a nightmare- but she was an angel. We didn't buy her a seat, so she sat on our laps the whole time. I brought toys and books, and snacks for her to munch. She slept some of the time, which was great, but when she wasn't sleeping, she was playing or flirting with the other passengers.
I had to change her diaper on one of the flights, which was something I was really afraid of, but the bathroom had a changing table (a small one) that folded down and it really wasn't that bad.
Can you take a direct flight? It was so much better to do direct than to have a connection. Also- we waited until the last minute to get on the plane. They allow you to board early, but we waited in the terminal and let her play on the floor on a blanket until we had to board- the less time on the plane- the better.
You can also ask when you check in if you can get a row with an empty seat- if the plane is not full, they can usually move you.
HTH,
Lisa and Riley