Выражение встречается в следующем контексте: Airline agrees that no more than two jumpseaters will be present during any operations. These passengers shall be either an employee of Airline or employee of UPS/

Заранее спасибо

If all the passenger seats are full, certain categories of airline employees (pilots always, and sometimes others) who have a "jumpseat pass" may be allowed to sit in this seat when they are travelling for free on a personal trip.

the confusing thing is that they talk of 2 jumpseaters. But since this is UPS, a freight operation things may be different. They may either have more seats in the cockpit than a passenger airline usually does.