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Of course a determined Terrorist can do it if he knows what he is doing and you don't have to keep too mumm about it seeing that Tom Clancy literally wrote two books with such an attack as the linking event years before 9/11. Dale Brown likewise wrote a cheap imitation based on the same theme a short while after Clancy did. In the second book, Clancy has somebody ask the FAA guy investigating the attack how did the attacker manage to pull it off, The FAA guy's reply, 'He knew all the correct buttons to push'.
To be honest the best comments I ever heard about this type of scenario was from (what I seem to remember) was the head of NORAD to a Committee (Which may have been something to do with the 9/11 Commission), where he stated 'If my interceptors have to shot down a hijacked airliner, it means that everybody else in the security apparatus across the board has FAILED!!!'