[Stealhead]

It was and still is very common for a pilot to not fly their assigned aircraft on a mission in the military.In an aircraft with only one or two crewmen they will simply fly the next available aircraft.

With heavies it becomes more of an issue and a mission might get scraped or delayed or another plane and crew will get the mission interdependent on if the plane is at its home base or is transient and away from home. At least in my experiences with the USAF and the ACC(mainly fighters) and AMC(cargo) that is how it worked out usually.With tankers there is always a back up sometimes it will be from a different squadron or even a different wing.Someone is always flying though or ready to fly that is why many Air National Guard units have some tankers assigned to them.

Sometimes a real issue will arise such a transient aircraft needing a major repair in that case another plane form the same squadron has to bring the parts if they are small enough other wise it may take weeks.I once say a B-1B get stuck for a week in Germany(not that they crew was upset) due to a serious engine problem they had to wait for a C-17 to have the space available to carry an entire engine for the B-1B.