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Hello.... reality calling....
Cdn CC130 is flying from Canada to Kabul... has mechanical problems while flying over US, Britain, France, Italy, Egypt, Turkey, India, Pakistan or pretty much any other place in the world... they can visit the military airport's parts department and get/scrounge/beg/borrow/steal/sign for the part that is broke...
Part goes into aircraft and plane sitting on ground can get back into the air... a simple concept.
If you are flying an "exotic" aircraft that everyone has heard about but nobody else owns.... guess what.... your plane stays on the ground, possibly becomes a hangar queen until such time as you can search the world and get the replacement part....
so which part of the concept "being realistic" do you have trouble grasping?