It doesn't matter because we're not dealing with any change among the elements (e.g. pilots & co-pilots) over time
Says who? Many games come to mind that allow the people variables to fill more than one position, especially when the rules limit some variables from doing so (e.g. B will attend class G or F but not both) here the last two rules state that Anna and Dave will ONLY fly in plane x or plane y and there is nothing elsewhere that would restrict the other variables from flying in two planes during the show.
Take question 20 for example: Anna flies in plane 4 (and cannot fly on any other plane "Anna will only fly in either plane 1 or plane 4.") and a pilot needs to accompany Dave on plane two it follows that either Cindy or Bob must fly with Dave, but there is no such answer. The "correct" answer is B (if C flies 3 then B flies two). I will create a scenario with Cindy flying the 3 plane and Bob not flying the 2 plane and you tell me which rule is violated.
Cindy and Dave fly in plane 2
Cindy and Ed fly in plane 3
Anna, Bob, and Fran fly in plane four.