I don’t let an airplane stop me from trying to get Dek to nap. At 18 months, it has gotten a little harder now that he is more aware of all there is to see and do on a plane, but even he winds down eventually and needs to shut off for a bit.
We generally go through his usual nap time routine, so it is no surprise when I try to get him to sleep. We read some stories while he hangs onto his little blanket he always sleeps with and a pacifier. Then I pop him in my Ergo Sport Baby carrier, pull the hood attachment up and place a light blanket over his head to block out as much light (and distractions) as I can.
I used to be able to get him to sleep sitting down. I just had to rock him a little. As he has gotten older, depending on his level of exhaustion, I sometimes have to do some aisle walking and bouncing. We’ll see how this continues to evolve as he gets older. I just approach each trip as a new experience and with very low sleep expectations. I maintain my sanity a little more this way I think.