You wrote:

""Arab terrorists are planning on boarding airliners, taking them over, and crashing them into buildings!" Okay, Mr. Bright Fellow in the FBI, now what?"

Hmmmm. It seems to me that having some forewarning of the method AND timing of the hypothesized attack, one would have one's guard up.

This rules out, of course, being blindsided.

You ask the rhetorical question: what would you do?

Well, to start with, I certainly would have had more than four fighters on strip alert in the NE (as the AF now claims at this late date), and even with only four, I would have scrambled them at the first sign of trouble, which is in fact already SOP according to FAA regulations.

(Of course, this is well outside FBI jurisdiction, so I've taken the liberty of widening your rhetorical question to include our entire defense/intelligence apparatus)

As we shall see presently, even with only four aircraft on strip alert, this small force would have been adequate to stop all of the attacks had it been deployed promptly in accordance with regulations.

Blindsided means being hit from a direction one is not looking or expecting.

In the face of the many warnings of an impending terrorist attack and considering the many blatant signs of terrorist focus on airliners, the lack of readiness by our defense forces to thwart this kind of attack on 9-11 falls well within the realm of criminal negligence, or worse.

sp