I think it is only spawning during late game, when the players themselves have access to flying units.
Now that you mention it, it does ring a distant bell, for this you are right, IIRC only after you researched the tech for producing them yourselves.....(or was after the first prototype of flying unit?....) A bit unfortunate that the techs are sometimes not a bit clearer, noooo not saying so directly but a slight hint :)
But wasn't the point :P ;) (yes call it nit-picking :D)
Might be true, but I don’t play classic SMAC often enough to notice an improvement on AI ;)
Anyway, I’m usually not playing on the highest difficulty, so I’m probably not the most apt to judge the AI level in these games…
I know what you mean, nothing worse than thinking: Hey I am doing alright and next moment being steamrolled by one of your opponents. :D
But worst I ever had was good old Civ (original). A wee bit slow start and next thing I knew, having a bomber next to my high-tech phalanx :D
And I think I will have to replay (again) now SMAX just to see how bad I suck :D