Originally Posted by doctor15

You know here best, but if I were you I would try to work out a scenario so that you are on the plane with her. That way she is not by herself or nervous for a longhaul trip on her own.

Anyways, here is what I did for my proposal. It may not work for your specific situation due to passport issues, etc, but just an idea:

I had her parents call her and make up some excuse that they needed her to come visit them a certain weekend (for reasons that they made up but were logical). Of course, she invited me to come along, and since I book ALL of our travel, I purchased our tickets as fully refundable. Secretly, I bought a (cheaper) set of tickets on a flight departing at the same time on the same airline to our actual destination. After she checked in, I cancelled the refundable tickets to see her parents. At the airport I looked at the departures board and said "wouldn't it be great if got on this plane and went to XYZ?". When she said ya, I said "ok lets go!"

Of course the only bad part of this plan was that by the time we were seated on the plane she already knew what was coming next. If you want to pop the question right there in the airport or on the plane it might work better though.