I did it a couple of times with a girlfriend in the pre 911 days. It sounds hotter than the reality, those bathrooms are tiny! Still, some things must be done at least once for the novelty and hilarity factor!
We did it in the bathroom once and then stuck to making out/fingering under blankets on international flights. I got a half of a BJ once on a long flight to Asia but people kept walking by and even in a dimmed cabin under the blanket you could see her head bobbing lol so I stopped her.
That was then! Now? I'd let her keep going and just smile at the people walking by!