It is not unusual for the desire to fart to go away after you stand up. So you are in the airplane lav and can't let it out there so you come back to your seat and then the desire to fart comes back. (If you sit down on the closed lav seat and wait a few minutes you will usualy succeed in getting the fart out.

Alternative: Bring along a bottle of perfume and rub a little of perfume on your fingers a minute before you decide to fart at your seat.

Travel tips:
http://members.aol.com/ajaynejr/travel.htm