let's say we have an option to spawn aircrafts in a "standby" state, if this is on the ground the plane would stay put, if this is in the air the plane would try to hold over the location (circling around). The player can switch into planes in standby, so you can spawn a number of planes in an airport, if one of them is destroyed or out of ammo/fuel, you can switch to a new one.
If Jundroo doesn't want to make ammo replenishment this could be a good alternative, too.

And then we can have a "follow" setting, which is essentially "aggressive" without firing weapons. If multiple AI planes are following the player, make them follow a "ghost plane" which is located exactly x wingspans off the player's wings. So if two AIs are following you, one would aim at the point one wingspan off your left, the other, one wingspan off your right.

It would be even better if we can set the "aggressive" target, effectively making the spawned AIs to attack certain ships, tanks or other map objects, or even other AI planes. Now we can have a 4 v 4 aerial combat.