The "almost" Times Square Bomb

[CRedskinsRule]

Here is one scenario, still doesn't explain the getting on the actual plane though: The FBI/Homeland Security had the airport wanted him to go through security so that they knew he had no explosives or weapons etc.

Of course if Jack Bauer had been in charge (and it wasn't the last episode) he would have gotten on the plane as Jack was running through the airport yelling "Turn that plane around NOW"!
I love 24, and imagine that this investigation was done at nearly as hectic a pace as that show runs at.