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You're seated on a commercial airliner filled with holiday travelers, recycled air and perhaps $30 less in your wallet, per bag. Shoulder to shoulder with two other passengers, the fuselage starts to feel like a sardine can. Your palms sweat as you look for any distraction, and that's when the flight attendant tells you how to use an oxygen mask and what happens if you land on water. You tell yourself it's statistically the safest form of travel, but the nervousness just gets worse.

If you're like 40 percent of airline passengers, you're scared to fly.

Why can't the brain calm down despite all the math being in your favor? And what can you -- and the airlines -- do to make the experience more comfortable? As in other areas of life, a little science can help.

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Experts point to takeoff and turbulence as the most worrisome moments for passengers.

Tom Bunn, a retired airline captain and licensed therapist, is the author of "SOAR, The Breakthrough Treatment for Fear of Flying." He cites 10 rapid-fire events that cause stress hormones to go bananas -- one after another -- shortly after the plane's door closes:

The engines rev for takeoff and the exhaust thunders. The acceleration of the plane pushes you back, recalling feelings of a physical intrusion, like bullying -- or much worse. The plane bumps as it rolls down the runway. The aircraft feels "flimsy" because the overhead compartments shake. The nose rises, and the plane lifts off, making you feel heavy in your seat. The landing gear noisily retracts.

"Ten seconds later," Bunn said, "engines slow and the nose is lowered for 'noise abatement' which causes passengers to believe the engines have quit and the plane is falling."

Passengers white-knuckle their way through the process, which Bunn points out is over in just about 2 minutes.

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Part of the problem with turbulence is that it's unexpected and nobody knows how long it will last. The takeoff is over quickly, but turbulence causes a release of stress hormones with every jostle, Bunn says.

"There's no light at the end of the tunnel," he says. "The person whose strategy is to keep the flight out of mind can't succeed with that strategy in turbulence."

A number of airlines offer courses to help you understand the mechanics of flying and stay calm during turbulence. And an app produced by Bunn's company shows passengers that their perceived free fall in turbulence "is really just a bit less than the 1G they feel when not in flight."

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Passengers look for various distractions to help take their mind off the flight. Larry Ventis, a professor of psychology at William and Mary, has done research on ways to alleviate fear using humor.

"Southwest flight attendants do often use humor during instructions," Ventis says, "but more could be done in this regard, pairing humor with flight-related content and imagery to establish a more comfortable perspective on flying."

Ventis points out that when anything does go wrong, passenger fears are heightened.

"The single biggest problem which fosters excessive fear of flying is the fact that anytime there is a crash of a commercial airliner it gets nationally and often internationally publicized," Ventis says. "Whereas the hundreds of thousands of safe flights every day get no publicity whatsoever."

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Routine maneuvers can feel more extreme than they really are. The nose of the plane seems to rise too quickly at takeoff, and when banking some passengers feel uneasy.

Acceleration makes the climb feel too steep, Bunn says. And it feels like the plane will slide backward -- like when your car is perched at the top of a hill. A more realistic view could help passengers see what's really happening.

"Cabin video from a camera directed straight ahead would help passengers see the nose is not too high or too low, and the plane is not banking too steeply," Bunn says. "When the anxious passenger looks out the window -- since it's a narrowed view -- a normal bank looks too steep. All they see is sky or ground."

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If using a tablet or laptop alleviates your fear, you may benefit from recent Federal Aviation Administration changes allowing electronic device use during takeoff and landing.

Gate-to-gate wi-fi was recently introduced by Southwest Airlines, who joined JetBlue, Delta, American and US Airways in offering expanded use of the technology.

If you don't like providing your own entertainment, ask before you book if the airline allows TV at takeoff and landing. Delta, for example, began offering this service before the new electronics rules went into effect and JetBlue gets high marks from flyers for its in-flight entertainment system.

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What else could the airlines do to make passengers more comfortable? Bunn says there's a simple upgrade. An anxious passenger could feel more in control by meeting the pilot before the flight, or talking to a flight attendant.

"The airlines could advise anxious passengers to make that known when (booking) so that the flight attendants can respond to them if they become anxious," Bunn says. "Though that might seem to the airlines to open a door to the person being a burden, it doesn't. The person just feels the airline is responsive, and that's all that is needed."

Building a relationship with the crew helps alleviate fear, it's inexpensive -- and it requires little training for airline staff.

"The flight attendant should simply engage the person in conversation," Bunn says, preventing the "imagination of disaster."