Originally Posted by
QRC3288
The fighters are primarily dispatched to view what's going on in the cockpit of a problem airliner and if there are any other visible issues, not necessarily to shoot it down. That's why they fly so close. If it was determined that the plane was indeed hijacked (and assuming those F-18s don't have missiles) and the intent was to crash the aircraft into buildings etc., presumably SAM sites could be utilized or other aircraft scrambled
The fighters are there to shoot it down should the need arises. There's no need for a missle to shoot down a plane. Machine gun fire from the fighter will more than be enough to shoot down the commercial airliner.