Decisive is storage with the cap up, ideally in hand luggage or in a case in the inside pocket; in this way both cartridge and piston pens stay leak-proof. Critical are the pressure-change phases during ascent and descent, in which ink can leak out; after the flight leaked ink should be wiped off. On reaching cruising altitude the pen can be used normally; ink flow is usually noticeably more saturated during ascent and descent. Lying storage in a suitcase can lead to ink residues in the cap but does not damage the writing instrument. The pressure differences are smaller in modern aircraft than earlier; balanced cabins reduce the leak risk.