On September 11, two F-15s were sent from Otis AFB in Massachusetts to protect Manhattan from further hijacking attacks. They weren’t scrambled until 8:52, six minutes after the first impact, and didn’t arrive at the scene until 9:25, 23 minutes after the second impact, and they reportedly didn't learn of any impact at all until they got there after the NY leg of the attack was complete. One of the pilots, code-named “Nasty,” lamented to the BBC “for a long time I wondered what would’ve happened if we’d, uh… been scrambled in time.” 
I would like to invite you to wonder along with him; imagine for a moment that the two Otis fighters had been scrambled “in time,” sent in the right direction, and flew full-blower. Imagine them arriving in Manhattan at, say, 8:54, just after the first plane had hit the WTC. They would be circling nervously in their F-15s, seeing United 175 coming in fast and low. Imagine the fighters rushing out to intercept it, ready to scatter the airliner over some farmer’s field before it scattered itself against and into the South Tower. Imagine them on the scene, ready to act and deal with the nightmares later, and prevent the second catastrophic collision and alleged jet-fuel-induced collapse that killed so many.
Now imagine they were left without legal authority to fire; imagine them asking and asking again as the hijacked airliner came into view “permission to engage?” and receiving the reply “do not engage.” We’d like to think they would pull the trigger anyway, and “take lives in the air in order to preserve lives on the ground,” the standard response in such an un-standard case. But it’s also possible they may have done their job and follow orders, even though the protocols mandated that they watch powerlessly as United 175 passed them by and slammed explosively into the South Tower. That would not look good for the government.
In fact, that would have been the situation if the pilots had been scrambled sooner. Every source agrees on this point; the fighter pilots sent to defend the skies were never instructed (and thus never allowed) to fire on airliners until long after all the targets had crashed. In fact, this itself may be the best clue in understanding the botched reaction up to that point. If not for the unlikely string of synchronized failures that kept all fighters well away from the hijacked planes, the lack of authorization would have been absolutely crucial and a political liability to say the least.
The Langley pilots did receive a vague order at 9:55 from the Secret Service to protect the white House. Recollections vary: “I want you to protect the White House” - ”The White House [is] an important asset to protect” - “Be aware of where it is… it could be a target.”  This was not taken by the pilots as a clear shoot-down order, signed off on by the proper authorities. Fifteen minutes later, in fact, the pilots were told they had “negative clearance to shoot.”  Jere Longman concluded that after patrolling Washington for hours “both Honey and Lou said that no one had given them any orders to shoot down a commercial airliner.” 
New York flight control mentioned to Otis pilot Nasty “if we have another hijacked aircraft we’re going to have to shoot it down.” He knew this was conversational and “not connected to the chain of command.”  “Only the President could make that decision,” Nasty explained to the Cape Cod Times, “and he was indisposed at a public event,” referring to his now-famous reading exercise at a Florida elementary school. 
 “Clear the Skies.” BBC Video. 2002.
 Thompson, Paul and the Center for Cooperative Research. The Terror Timeline: Year by Year, Day by Day, Minute by Minute. New York. Regan books. 2004. Page 436.
See . Page 453.
 Longman, Jere. Among the Heroes: United Flight 93 and the Passengers and Crew who Fought Back. New York. Harper Collins. 2002. Page 222
 See . Page 440.
 Dennehy, Kevin. “'I Thought It Was the Start of World War III'” The Cape Cod Times. August 21, 2002. Accessed November 13, 2004 at: http://www.poconorecord.com/report/911-2002/000232.htm.