> If the pen’s ink reservoir is partly empty, so that it contains an air bubble, and if it’s positioned nib down, then, when you go up in an airplane, the bubble will expand as the ambient pressure drops, forcing ink out the nib. Once I figured that out, I got in the habit of making sure my pens were positioned nib up when taking off in an airplane. If I have time I’ll also refill the pen before departure, to minimize the size of the air bubble.

Finally! this was one of those things that bothered me for many years, but not enough to spend time to research :) . Thank you!!