Answer:
Some of the terrorists had lived in the United States for more than a year and had taken flying lessons at American commercial flight schools. Others had slipped into the country in the months before September 11 and acted as the “muscle” in the operation.
The 19 terrorists easily smuggled box-cutters and knives through security at three East Coast airports and boarded four early-morning flights bound for California, chosen because the planes were loaded with fuel for the long transcontinental journey. Soon after takeoff, the terrorists commandeered the four planes and took the controls, transforming ordinary passenger jets into guided missiles.
AND After 9/11, all passengers 18 years or older, must now have valid government-issued identification in order to fly.
