"small planes"
I just don't think we have the means to stop small planes from flying into buildings/refineries/chemical plants etc. When you think about it...the terrorists don't have to bring anything with them into this country. Just slip over the border from Mexico into Texas and use the weapons/explosives/planes that are already here.
Or hide the planes in small hangars, barns, storage facilities etc- then fly them very quickly toward the desired city...eject the bomb or whatever. By the time our fighters get there- the deed could well be done. Look at those little planes that flew into Philly and DC airspace...
"I just don't think we have the means to stop small planes from flying into buildings/refineries/chemical plants etc."
I don't know that small planes can do that much damage crashing into things. I've seen small planes crash into homes around me; a small plane crashed into that building FL not too many years ago; and one crashed into the Empire State Building at one time. I mean, they do damage but not catastrophic. Maybe if there are some kind rockets involved or chemical dumping (like from a crop duster).