Question

Why does a fountain pen start leaking at higher altitudes

Answer 1

Gravitational force decreases at higher altitudes that leads to ink leaking..
 

Answer 2

The pressure at higher altitudes is comparatively less, so to equalize the pressure difference ink starts moving out from the pen which has a relatively high pressure. Same applies to tooth paste as well as bleeding from nose at such altitudes.So at higher altitudes fountain pen starts leaking......