In case anyone happened to be interested in this, I did actually figure something out. Using Menyoo, there is a Task Sequencer which (With a looootttt of patience) you can actually use to script an AI to walk to a plane, get in, and fly. I'm just having trouble getting them to stick to the taxiways and return to the runway.
I might post updates here as I figure them out, might upload the Menyoo world file if people are interested.
@ArmaniAdnr Pro tip: i'd suggest you watch missions cutscene compilations and watch mission gameplays.
when for example you see a character do a cool pose, remember what the pose was about what was the character holding in that scene(object,prop,car,weapon...ect), the name of the ped who was he interacting with (other peds), the name of the mission... ect and use that to your advantage as keywords to look for animations in menyoo. It may take a while to find some good animations at first but once you understand how to look for animations you'll get enough experience to look for more complicated animations.
pro tip 2: if you're looking for animations for the main characters look for animations using these keywords
1- player_one (Franklin)
3-mph 'original online heists'
4-player_zero (Michael if i'm not mistaken)
5-player_two (trevor if i'm not mistaken)