I'm worrying about the exact same thing as you right now. My 15 mos DD is the same way - I always put her in crib awake, and she has to do her standing/rolling/moving around WITHOUT ME before finally falling asleep, on her tummy all the time. And I'm traveling with her overseas in 2 months.
One hope I have is that she's finally started to sleep in her carseat. Does your DD do that? Mine used to scream in her carseat when she's tired and wanted to sleep, but now she sleeps in there when the car is moving (this happens now once a week, as one class we're going is cutting into her naptime a bit). We recently had a 5-hour road trip peacefully as she slept in her carseat for 1 hour at a time.
So I'm hoping that on airplane she can do the same - I'm getting her own seat and will strap her in and give her bed toys, and try to be out of her sight...we'll see how it goes. But whether she sleeps well or not, she'll be exhausted anyways between the traveling and jet lag, so I'll take it really easy for the first few days. If your trip is before April, please let me know how it went