So, I'm having trouble understanding how there could be an issue with the nib kept pointing up during travel - unless a bubble is trapped in the cartridge underneath the ink. The change in air pressure affects the air within the pen. As altitude goes up, the air becomes thinner and evacuates from the interior of the pen (expands). This is when the issue could possibly occur - if the pen nib was down, the ink against the feed, or air trapped in the reservoir/cartridge. On returning from high altitude the pressure increases, which pushes denser air back into the reservoir (bubble contracts).