When aircraft are assigned to a city, are they "garrisoned" there? If so, are they covered by the "garrisoned units have no upkeep" bonus from the Tradition culture tree?
My (apparently-dashed) hope was that Triplanes/Fighters/Jet Fighters could be set to intercept and would be upkeepless, but that apparently isn't the case.
Best Answer
The short answer is no. You can't.
Source: look at Thresian's answer. To question number 2.