I guess it "could" have been done with only desktop flightsim experience. But the chance of missing would just be too great. (Seen from the terrorists' point of view
)
This was a well planned, and well coordinated attack. And the result was two extremely precise hits in a one-shot-chance at the WTC, and one on the Pentagon. I don't think the terrorists would have "run the risk" of failing by not having prepared themselves well enough.
If the question is if this
could be done again by a psychopath who's only resource is a PC game, I guess the anwer is yes. But his chance of "succeeding" would be
extremely limited.
If the question is if the attacks on WTC and Pentagon were performed by people who's only training was on on a PC game and maybe a few hours in a small GA airplane, the answer is definitely
no.
Nick.