I can't see any intelligent terrorists setting up their missile in front of security cameras, security patrols
That's a bit naive isn't it? Before 9/11, it might have been said that an intelligent terrorist wouldn't be on the 'plane they crashed. If they are fanatics, and most of them are, they will go kamikaze. They only need to whip it out a few seconds before the a/c goes over, or have it set up inside a van and not immediately visible.