Originally Posted by
cordelli
There is no guarantee any fountain pen won't leak in a flight, but I have found that keeping it point up and only about half way filled makes a huge difference if possible.
I usually keep them in a ziplock bag just in case if there both in the suitcase and carryon.
It is the point up saving you there. The best way to carry a fountain pen on a plane is point up, and nearly full cartridge. It is the air that expands due to the decreased cabin pressure. If the point is up, the air just goes out and the ink stays put. If the point is down, the air is trapped by the ink (since the air goes up of course) and so when it expands if forces ink out. Likewise, the less air in the pen, the less volume change from the change in pressure. The ink doesnt change much if at all since it is a lot denser.