NotSoFantastic....Atta was'nt in the flight deck; they were sitting in first class, but seperately, when they commandeered the aircraft in question. The FBI report lists the seats they were assigned, and all hijackers were in the pax cabin.
In the US, flight deck doors won't matter if pilots are armed---the hijackers will just be shot once they break down the door. Nobody will ever commandeer a jet and use it as a suicide bomber again, if pilots are armed.