Air traffic controllers across the United States were the first to realize the hijackers' deadly, coordinated mission on Sept. 11, leaving deep scars on people whose job requires total concentration and control.
Controllers at the Boston Center knew American Airlines Flight 11, which departed at 7:59 a.m. ET from Boston for its flight to Los Angeles, was hijacked 30 minutes before it crashed. They tracked it to New York on their radar scopes.
"I watched the target of American 11 the whole way down," said Boston controller Mark Hodgkins. But it was only when the television pictures of a burning World Trade Center tower came on, that he knew why the flight had disappeared from his scope.
For Doug McKay, a 20-year veteran at the Boston Center, the hijacked flights hit much closer to home.
Before he left for work on Sept. 11, he heard on radio and television that the World Trade Center's North Tower had been hit. As he was watching the news report, he saw the second flight slam into the South Tower.
Not knowing a flight from Boston was involved, McKay left his house in Nashua, N.H., and drove the 25 minutes to work, listening to the news.
That morning, McKay's wife Susan, an assistant vice president for the retail conglomerate TJX Companies, left on a business trip. She was on American Airlines Flight 11.
"At the front door of the center was a supervisor and two controllers from my area and the supervisor asked me what flight Susan was on," he recalled. Once McKay told him, his supervisor told him to come with him. "And that's [when] I knew that… the flight Susan was on was involved in this."
"In that instant, it's just like someone hit you in the stomach, you know," McKay told ABCNEWS. "It's just unbelievable." He then had to go home and tell his 14-year-old son and 9-year-old daughter they had lost their mother.
Even worse, if McKay had worked an earlier shift that day, there was a good chance he would have been the controller who tracked the hijacked flight from Boston that his wife was on.
"I could never see myself sitting in front of an air scope again," he said. "I don't believe I have the concentration, or even probably the courage."
A few years away from retirement, his fellow controllers transferred their own vacation and leave time to him so he could retire early to raise his two children and do something other than control airplanes.
"And I have to start some new life," said McKay, "which I don't know what it's going to be yet."
Others Recall Trying to Contact Planes in Vain
John Werth, a controller in Cleveland, first heard the screams from the cockpit of United 93, and tried in vain to contact it. That flight crashed in a Pennsylvania field.
Despite what he went through, he took only a short break and came back for a second shift on Sept. 11. He has not missed a day of work since.
But like McKay, for others, it was harder. Washington controller Danielle O'Brien handled American Airlines Flight 77 on take-off and then watched as it headed back at full speed towards the Pentagon. "They were blips and [then] they were human lives," she said.
O'Brien, who is now back at work, took several weeks off, because she was deeply shaken by what happened.
"I'll see it for the rest of my life," she said. "I'll hear it for the rest of my life."
Like the rest of America, the air traffic controllers, at a convention this week in Cleveland, Ohio, have had to learn how to cope with the tragedy.
"We surely weren't trained for this, we didn't expect this," said Brad Troy, who has been a controller for 18 years. "Controllers that day were uniquely wounded."
Troy and other union controllers have been called on to counsel more than 1,500 of their members since Sept. 11. "There's a lot of second guessing," he said. "What could have we done better, how could we have prevented this, why didn't we see this?"