When my daughter was 18 months, we flew back from Chicago to Phoenix. My daughter threw up and screamed for the entire flight. I've never taken her back on a plane since and that was 9 years ago.
I feel your pain! After taking my 12 mo old son from Atlanta to Madrid Spain, and his being sick and crying for 7 hours, I have never got in a plane again. Well, except the return trip, and that’s because I didn’t have a choice. Since then, if my parents want to see their grandchildren, they are welcome to come over here!