[InitialLastName]

If they had locked and reinforced the cockpit doors, 9/11 wouldn't have happened.

That's all it takes.

[squarefoot]

Before 9/11 there was no perception of that necessity though.

[davidf18]

Well, Israel had done it for quite some time thanks to terrorists hijacking their planes. Plane hijackings have been going on for other countries for some time.

Also, IIRC, El-Al has an air martial (again former military in every case) on each flight.