[Vash02]

Sorry guys, its not that simple. You cant let people onto a plane without some screening. Rather than flying a plane into a building you will have a few thousand gallons of burning jet fuel and tons of wreckage raining down on New York.
They tried it in 2006 and people have been banned from bringing drinks onto a plane ever since.
Dont believe the depths these sort of people will drop to to kill people. They used a mentally retarded man to plant a bomb in a resturant in Britain. It wasnt the most effective strategy but dont doubt they will use a small children, disabled people and other vulnerable people to pass weapons and bomb parts through security.