Like millions of other Americans who were glued to their televisions Thursday night watching the aftermath of the flight that ditched into the frigid Hudson River, 82-year-old Joan McKown of San Marcos, Calif., got just a bit emotional when it was revealed that there were no serious causalities.
"I was tearing up and was so happy everyone was OK," she said.
Unlike most people, McKown has firsthand experience. Like Capt. Chesley Sullenberger III, the pilot whose actions saved 150 passengers aboard U.S. Airways flight 1549, McKown has experienced being a member of a flight crew during a mid-air disaster. And like Sullenberger, she was able to react in what most would agree was a calm and heroic manner, tending to passengers as her own life was in eminent danger.
Experts aren't sure exactly what causes people to behave heroically under stress. But they have some theories -- one known as "heroic imagination," and another asserting that a well-trained person essentially is able to switch to autopilot in a crisis situation when an untrained person's impulse might be to freeze up.
McKown was a 22-year-old stewardess for United Airlines when she was tested in a crisis. On a clear August night in 1950, as she was working a nonstop flight from L.A. to Chicago, a faulty propeller ripped off the airplane, causing an engine explosion that sent a propeller slicing through the hull like a can opener.
"It was such an explosion," she recalled. "We just all flew toward that opening."
McKown said she was thrown 20 feet and hit her head. When she regained consciousness, she said, the plane was still in the air -- and she found herself surrounded by debris and frightened passengers with 250 feet of the fuselage's top completely missing.
"I woke up and I thought, 'Oh my God, this airplane has been blown to pieces,'" she said, adding that the flight path over the Colorado Rockies left them few options in terms of an emergency landing. "There was no place to land for 25 minutes."
But despite the horror of the situation -- and the fact that she had sustained a head wound that was streaming blood down her shirt -- McKown soon began going from row to row, checking on passengers.
"It was so loud, there was so much wind, you had to scream in their ears and ask if they're all right," she recalled. "We couldn't hear them if they were [screaming], but I think that was something that kept them calm, because they couldn't hear anybody else yelling either."
So what makes a hero respond in a heroic way? Cleveland Clinic psychologist Scott Bea said researchers are still struggling to find an exact answer to that very question.
"It's a poorly studied phenomenon," Bea said. "We probably know much less about being a hero than we'd like to."
But he added it is likely that a concept known as "heroic imagination" lies at the root of certain people's ability to react heroically in a dangerous situation.
"Certain people have actually envisioned themselves in these scenarios and thought about how to act," he said. "Pilots, I can guarantee you, have engaged in this heroic imagination probably more than ordinary citizens. I'm guessing that flight crews have gone through this heroic imagination, as well."
What psychologists call heroic imagination, many pilots might call training. And Dr. Charles Raison, assistant professor in the Mind-Body Program at the Emory University School of Medicine's Department of Psychiatry and Behavioral Sciences, agreed that a familiarity with at least the possibility that such a situation could arise probably helped Sullenberger save both his own life and those of his passengers and crew.
"What are the things that make people completely lose it? One of the major ones is unexpected trauma," Raison said. "The 'new' is very shocking. Training ensures that these pilots have a sense that they know what to do -- they don't have to cogitate; they don't have to think about it. In a time of stress, it's good to have a memorized program."
But heroic imagination is not the only psychological impulse that can influence one's decision in a disaster. On the other side of the coin is a concept called "behavioral inaction."
Ben Sherwood, author of a new book called "The Survivors Club: the Secrets and Science That Could Save Your Life," says that within all of us lurks a so-called "disaster personality." Think of it as your mind's set plan for reacting to a sudden crisis. And while a few of us may be hard-wired to act heroically, he said that most people simply freeze when things get too intense.
"When you look out the window and see the wing of your plane burning, you've never seen that before," Sherwood told "20/20." "And your memory searches for what to do in this situation. Finding nothing that compares to a wing burning, you search again. And it becomes an endless loop of searching and having no action."
Journalist Amanda Ripley, who has covered dozens of catastrophes and is the author of the book "The Unthinkable," said that our disaster personalities can have be a huge factor in whether or not we are able to survive a crisis.
"I think the thing that's most surprising is that your biggest threat is that you will move too slowly or shut down altogether," she told "20/20." "We think people will panic, and that almost never happens.
"The more I looked at this, the more examples I found, in sinking ferries, in plane crashes and burning buildings, you name it -- there is a good number of people who literally stop moving and they shut down."
Bea was quick to point out, however, that just because a hero is able to rise to the occasion, it doesn't mean that he or she is impervious to fear. On the contrary, psychologists know that the body's natural response to fear often helps get us out of dicey situations.
"I'm inclined to guess that at some level, physiologically, he was panicked," Bea said. "But when you're anxious in that way, you are also very vigilant, alert and able to respond."
Still, there remain elements of heroic action that even psychologists can't fully explain.
"I think what impressed me the most about this guy was that at the moment he lost the engines, he knew he couldn't land at LaGuardia," Raison said. He added that Sullenberger's instinct under pressure to forgo a different airport in New Jersey, choosing instead to ditch the Airbus A320 in the Hudson River, may have saved lives on the ground as well.
"There is a human tendency to say, 'That's an airport; I'm going to get there no matter what,'" Raison said. "What amazes me is that he was able to say, 'No, I'm not going to get there, I'm going to put it into the water.'"
And perhaps the biggest mystery of all is the typical low-key response to the hero's welcome once the danger has passed.
"When you listen to what they say afterwards, they'll say it's not a big thing," Bea said. "It is interesting that heroes find their responses quite ordinary, even though they have done something that in everyone else's eyes in quite heroic and extraordinary."