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MILES O'BRIEN, CNN ANCHOR: The first volley in the war on terrorism began the morning of September 11, and the first people to engage the enemy that morning were air traffic controllers. In FAA radar control rooms all along the East Coast and into Ohio, there were scenes of horror and heroism.
O'BRIEN (voice-over): Stroke by stroke, the hijackers painted a diagram of their evil plot on radar screens in air traffic control centers in New Hampshire, Ohio, New York and Virginia that morning. But it happened too quickly and in too many places for controllers to see the synchronicity as it unfolded.
The fog of war had enveloped air traffic control. The first salvo came at about 8:15, when a controller cleared American Airlines Flight 11 to climb from 29 to 35,000 feet.
GLENN MICHAEL, BOSTON AIR TRAFFIC CONTROLLER: There was no acknowledgment from the pilot on that transmission. Further attempts by our controllers to contact American 11 were fruitless. We never re-established contact with the aircraft.
O'BRIEN: American 11's transponder, which transmits altitude and air speed, went silent. Controllers heard a stray radio call. "We've got planes," declared the voice. It now seemed obvious this was a hijacking. They responded as they were trained.
LINDA SCHUESSLER, WASHINGTON AIR TRAFFIC CONTROLLER: From the air traffic perspective, the handling of a hijack would be whatever the aircraft needs or wants, we would give it to them.
O'BRIEN: At 8:40, controllers picked up the phone to notify NORAD, which scrambled the fighters. One minute later, a controller in the tower at Newark Airport cleared United Flight 93 for takeoff. 93's flight path crosses United 175's. Although its transponder was still on, it had ceased talking to controllers. At 8:43, New York controllers made their call to NORAD.
Three minutes later, American 11 hit the north tower. Controllers in the New York terminal radar approach control facility, or TRACON, tracked United 175 as it turned left over New York Harbor toward lower Manhattan.
MICHAEL MCCORMICK, NEW YORK AIR TRAFFIC CONTROLLER: Probably one of the most difficult moments of my life was the 11 minutes from the point I watched that aircraft when we first lost communications and to the point that aircraft hit the World Trade Center. For those 11 minutes, I knew -- we knew what was going to happen.
O'BRIEN: In Newark tower, they could see the plane make its ominous turn. They watched in horror as the tragedy unfolded.
(on camera): With the World Trade Center in flames, controllers threw out their old hijacking playbook and started making up some new rules. Two minutes after the second tower was struck, the Boston center banned all departures in its sector. Two minutes later, 9:06 a.m., Boston, Cleveland and Washington ban all departures of flights headed toward New York. And then two minutes later, at 9:08, New York slams the door entirely, banning all flights headed its way.
(voice-over): In Overland, Ohio, at the en route facility known as Cleveland Center, things got very busy very quickly. Controllers began holding dozens of New York-bound planes in their airspace while looking for the signs of more trouble.
RICK KETELL, CLEVELAND AIR TRAFFIC CONTROLLER: That's where Delta 1989 came in.
O'BRIEN: Delta 1989 fit the terror profile. A 767, it left Boston, bound for Los Angeles, only five minutes behind United 175.
KETELL: We told the controllers not to share what they knew, because at that point, folks had seen the aircraft hit the trade tower, obviously, in the cafeteria, where our television is located, and they knew pretty much that things were pretty extraordinary.
O'BRIEN: Meanwhile, United Flight 93 appeared on radar screens here. The first call from the pilot, routine. Controllers remember him sounding cheerful. Then at 9:32, they heard the first of four troubling radio transmissions.
KETELL: The first transmission that sounded like struggle in the cockpit. It was pretty clear. And then we had a second transmission, also, that was a struggle in the cockpit, and you could hear the pilots -- what appeared to be the pilots yelling, "get out, get out." And a lot of other noise that appeared to be a struggle.
O'BRIEN: At first, they suspected it was Delta 1989, and their fears grew when it asked to land in Cleveland. As it turns out, the crew was ordered to land by the airline.
Before controllers could check, though, their radar screens pointed them in a different direction. It was United 93 that had abruptly descended and then climbed to 41,000 feet without approval.
KETELL: The information traveled throughout the control room with lightning speed, and everybody kind of took a deep breath and realized, wow, we're part of this, too. There was no doubt what we were dealing with.
O'BRIEN: By now, controllers at Washington Center were dealing with their own unresponsive airplane. American 77 departed Dulles for Los Angeles at 8:21, just as American 11 had stopped talking to controllers. The plane flew as far west as Indiana and then took a U- turn toward the heart of the nation's capital.
(on camera): It crashed at 9:40. Five minutes later, at the FAA Command Center in Herndon, Virginia, they made a stunning, unprecedented decision -- clear the skies, have every aircraft over the continental United States on the ground as quickly as possible.
And there were more than 6,000 aircraft to deal with at that moment. There were no procedures for this; no one had even contemplated, much less practiced, such a scenario.
FRANK HATFIELD, NEW YORK AIR TRAFFIC CONTROLLER: We started giving pilots options of the closest airport and started landing those aircraft.
O'BRIEN (voice-over): As that order came down, United 93 was heading southeast toward Washington; its altitude-reporting transponders silent. Controllers heard a pair of radio calls which sounded like PA announcements. "We have a bomb," they claimed.
KETELL: The aircraft turned abruptly to the east, and then hard right turned abruptly to the south, due south, and then eventually disappeared from the radar.
O'BRIEN: It was 10:07. Controllers were now focused on emptying the skies, offering little explanation to incredulous pilots.
HATFIELD: We just asked them to make sure that their cockpits were secure, and we solicited their airport of intended landing. That's all.
O'BRIEN: By 12:15, two and a half hours after the order was issued, four hours after the hijacking of American Airlines Flight 11, the airspace over the continental U.S. was clear. Only military and emergency aircraft were in the air now.
(on camera): Is it your hunch, your conviction, whatever, that there were planes out there that were thwarted by the FAA action?
MCCORMICK: I don't think it could ever be proven. However, I feel very comfortable in the knowledge that the air traffic controllers were the heroes that first rose to the defense of our country on September 11. And the decision to remove weapons of destruction from terrorism that day, in fact, saved many lives, and there were other opportunities, and there were other plans that we intervened in.
O'BRIEN (voice-over): We may never know for sure, but after that brutal, breathtaking morning, a silent sky is what the nation needed that afternoon.
CATHERINE CALLAWAY, CNN ANCHOR: It was a brave move by the air traffic controllers to clear the airway. But helpless, the helplessness that he expressed during those 11 minutes must have been horrific for him.
O'BRIEN: Yeah, I mean, you can imagine the torment of it all and being completely powerless to do anything about it. You know, they had made the calls to NORAD to scramble the fighters, but the system, as it was then, made it rather cumbersome. It took a matter of several minutes before those fighter planes in this case -- talking about New York from Otis Air National Guard base on Cape Cod were airborne. By the time -- as a matter of fact, they were 71 miles away from lower Manhattan when the second plane, United 175, hit.
So they were powerless, yet they were brimming with missiles, literally, to do what would have been an unthinkable thing, shoot down a civilian airliner, but there was nothing they could do about it.
CALLAWAY: Yeah, but some things have changed.
O'BRIEN: Yes. The key thing that we have to remember here is that air traffic controllers, first of all, now have an entirely different mind-set, as we all do, about hijackings.
You heard in that story one of the FAA officials talking about the basic theory was mollify the hijackers, comply, submit, and you'll end up on the ground somewhere and negotiation begins, and the chances are everybody will walk away safely.
Obviously, that paradigm has changed completely since September 11. And what the FAA has done is, first of all, they are spring- loaded for this sort of thing, as are passengers, for that matter, and secondly, they have a communication link with NORAD, which is instantaneous. Literally, one phone call, they will pick up, the person responsible for scrambling those fighters that are on the standby is on the other end of the line, and that scramble will happen in a matter of seconds, or at least the order will come in a matter of seconds. They'll be in the air inside 10 minutes, as opposed to several minutes.
CALLAWAY: And you know, you have to worry and you have to think -- not to think in the dramatic sense of the worst happening, that the communication has to be almost perfect between the pilots now and the air traffic controllers. Should be some miscommunication that there is a problem on the plane or there is an issue that needs to be settled because they are able to respond so quickly?
O'BRIEN: Well, exactly, and you know, it's interesting, because of course the controllers, having lived through this experience, are going to be always listening for this sort of thing, and what are frequently very routine sorts of communication losses caused by technical problems, transponders going on the fritz, whatever the case may be, now arouses tremendous suspicion, and in many cases since 9-11 -- I don't have the numbers right in front of me -- dozens and dozens of cases have ended up resulting in those F-16s or F-15s being scrambled, and folks in 767s on their way to L.A. suddenly seeing the military jets off their wing tip.
Now, that is a troubling thing, but it really, if you think about it, it should be comforting. CALLAWAY: It should be comforting. But, you know, unless you are on the plane...
O'BRIEN: Yeah, yeah.
CALLAWAY: Then it's not very comforting.
O'BRIEN: That will wake you up.
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