This topic may have been raised before so if so I apolagize.
I could not help thinking that all the aircraft used for the suicide attack on 11 September were virtually empty - 44 passengers on a 757 etc. This cannot be a coincidence! The hijackers delibrately chose airlines with few passengers because they did not have guns or other really lethal weapons.
How did they know which flights to choose?
Both United and American allow you to pick your seats from a seat map when you book on the internet. I think Delta have the same system. From this you can tell if the flights were full or not. Also you pick your seats BEFORE you make payment so you can pick the most empty flight. I have used this to pick lightly loaded flights myself!
Much as I find this system helpful maybe it should be abolished! Make it one more hurdle the terrorist need to overcome!
I was just on packed NWA DC-10 flight - It is hard to imagine so this plane being taken over unless the hijackers had guns.