When an airplane flies at a higher altitude,it is not advisable to keep a fountain pen in one's pocket. Why?

(N/A) As the altitude increases,the atmospheric pressure decreases. The ink inside the fountain pen's reservoir is filled at ground-level atmospheric pressure. When the airplane flies at a high altitude,the external atmospheric pressure acting on the ink decreases,while the pressure inside the pen remains higher. This pressure difference causes the ink to leak out of the pen and onto the clothing. Therefore,it is not advisable to keep a fountain pen in a pocket while flying at high altitudes.