[JTHomes]

They would have to get the explosives on board. There in lies their problem.

Yes, and the solution apparently is to have 14 terrorists each bring 1 or 2 of the 5 of so ingredients required to make a small bomb. If one or two get searched or have to ditch their contraband, others have redundant supplies. It wouldn't take much to build something as strong as a stick of dynamite, which placed in the right spot could have that plane headed down.

[Steve_Seattle]

I'm no chemist, but I wonder if there are explosives which could be assembled on the spot from separate ingredients which - on their own - would escape detection. But I think the terrorists are probably more sophisticated than that; what worries me are explosives disguised as - or hidden within - ordinary objects such as cell phones or shoes.