...is to ensure that aircraft are secure. There are more forms of non-lethal weaponry than there are trolls on Slashdot. (Well, almost. :) It is absurd that 114+ people cannot protect themselves adequately against less than half a dozen.
Yeah, yeah, I've heard a lot about "Sky Marshals", and the use of lethal force. But think about this - an aircraft's fuselage is little more than aluminium film, stretched over a very minimal skeleton. On the inside, you've a bit of plastic to prevent anyone accidently putting their arm into the stratosphere, and incidently cause explosive decompression.
On the other hand, your average bullet doesn't stop when it hits plastic. Arms inside an aircraft are extremely limited, because you have to use only those things which cannot destroy the plane. (DUH!)
That limits you to non-lethal weaponry (eg: laughing gas, pepper sprays, rubber bullets, tasers, those new microwave guns the military have, etc.)
In which case, the use of Sky Mashals is somewhat redundant. The passangers and/or crew could subdue any malicious person or group, without any risk.
The use of the USAF is also questionable. They WERE alerted, in Tuesday's attack, but launched late. Reason unknown. They missed the hijackers by about the same length of time as their delay. If I were a cynic, I'd ask if they waited deliberately, so that they could get a financial boost from the Government, afterwards.
In fact, I am EXTREMELY cynical, about the entire event. Too many key people were out of place, including an entire FBI rescue team, and too many things took FAR too long. You've got to realise, and this is true for all air forces, crews are ready to scramble at a moment's notice. They have to be. You can't exactly ask your enemy to wait, until you've finished your coffee.
Interceptors of the kind used are not exactly slow, either. To get from the nearest airbase to the Pentagon, at maximum speed, is not going to take tens of minutes. These are supersonic aircraft, not model kites!
Would the US air force -really- delay a response for money? When you're talking tens of billions, to a cash-strapped organization where it's top-line fighter-bomber is almost three decades old, and where the only product under development (the Osprey) is spending more time crashing than Windows, I could certainly see the possibility of someone "taking their time".
Is that likely, though? The only ones who know are those in the USAF, and there's no way in hell they'd say if it was. The only way you could really find out is by seeing how hard they lobby for money in the next budget, and also by any correlation between accidents and opportunity for budget improvements.