Up to 40 percent of Americans fear flying. It’s easily treated.

Fear of flying afflicts as much as 40 percent of the U.S. population. The nation’s armrest-grippers may be heartened to know that “aviophobia” is perfectly normal, and easily treated.

Only about 5 percent of Americans have aviophobia so severe that they cannot fly. The earthbound population rises with every new aviation horror story, like the Lufthansa Airbus A330 that went into free-fall over Tennessee on Wednesday after hitting severe turbulence. Several passengers landed in the hospital.

Many more people board airplanes with unease, suffering in silence as the craft lurches improbably into the air, swallowing curses when it hits “rough air,” digging nails into upholstery amid the controlled chaos of landing.

“Do they show it? No,” said Jonathan Bricker, a University of Washington psychologist who studies anxiety in air travel. “But they might have an extra drink. They might sleep more. They might not look out the window. And it’s not the whole flight. It’s takeoff. It’s landing. It’s turbulence.”

The full extent of aviophobia is one of psychology’s fuzzier statistics. One 2016 research paper stated its prevalence as a range “from 2.5 percent to as high as 40 percent.” The National Institute of Mental Health does not collect data on fear of flying.

A long-running poll by CBS News and YouGov found that, as of 2015, only 41 percent of Americans surveyed reported being “not at all afraid” of boarding an airplane. The share of Americans without fear of flying dipped to 38 percent after the Sept. 11, 2001, terror attacks, according to earlier Gallup polling.

Both surveys suggest that, even in the best times, nearly half of the American public harbors some fear of air travel.

Lisa Hauptner was fine on airplane flights until a moment in her late twenties, when suddenly she wasn’t.

“I reached a point where the anticipation of my next business trip resulted in an Amtrak from New York to Tampa,” she recalled. “It’s a long, horrible ride. When I got back, I realized I had to do something.”

Hauptner enrolled in a fear-of-flying program called SOAR, run by a former commercial pilot named Tom Bunn. It worked so well that Hauptner quit her finance job to help Bunn build the program.

The best aviophobia programs boast a success rate of 90 percent, said Barbara Rothbaum, a psychiatry professor at the Emory University medical school. Rothbaum has pioneered one of those programs, which uses virtual reality to replicate airplane flight — turbulence and all — to help patients conquer their fears.

A virtual airplane “works just as well” as a real one, Rothbaum said, and it’s far more practical in an era when one does not simply walk into an airport.

Treating aviophobia starts with identifying its source. Researchers generally divide aviophobes into two camps. One group fears fiery death in a plane crash. The other fears confinement in the cabin, a form of claustrophobia. Some scholars add a third group, which doesn’t suffer claustrophobia per se but fears the onset of a panic attack while trapped in the plane.

For the small group of Americans who will not fly for love or money, aviophobia can cancel reunions, vex vacations and destroy careers.

“It gets in the way of your life,” said Luana Marques, an associate professor of psychology at Harvard Medical School. “If somebody has a phobia of flying, they may get a promotion and get offered millions of dollars, and they won’t take the promotion because they don’t want to fly.”

Fear of dying in a commercial air crash is, of course, utterly irrational. Two people, in all, have died in U.S. commercial airplane crashes since 2010, according to industry data. The nation’s last large-scale air disaster was Continental Connection Flight 3407, which stalled during landing maneuvers in 2009 and crashed into a house, killing all 49 on board.

Aviophobia feeds off of something called confirmation bias. The irrational brain scans the universe for any data that might confirm the illogical fear. Even reports of comparatively trivial harm, such as last Wednesday’s Lufthansa drama, feeds the fear.