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Flights headed to Honolulu, Tampa, Fla., and Frankfurt in recent months hit turbulence so severethat some passengers and crew ended up in the hospital with injuries.

Actor Matthew McConaughey was a passenger on the Lufthansa flight to Germany. In a recent podcast interview with Kelly Ripa, he described seeing red wine suspended in midair before it crashed down. 

“It was a hell of a scare,” Mr. McConaughey, who wasn’t hospitalized, said on the podcast. “A complete loss of control.” 

Pilots and meteorologists say bumps are a normal part of flying. The Federal Aviation Administration is still investigating the Lufthansa flight. But meteorologists say climate change is distorting the jet stream, making a certain type of severe turbulence—called clear-air turbulence—more likely in the future. 

Severe turbulence injuries are rare. Between 2009 and 2022, 163 people were seriously injured during turbulence, according to National Transportation Safety Board data. Flight attendants, who are more likely to be standing during flights, are most likely to get injured, the data show.

What Is Turbulence? A Pilot Explains How It Happens, Even in Clear Skies

https://www.wsj.com/video/series/travel-guides/what-is-turbulence-a-pilot-explains-how-it-happens-even-in-clear-skies/152CAF18-F5BC-4395-9009-397B2DB1C8D4

Illustration: Alex Kuzoian for The Wall Street Journal

What the science says

Though technology that reports turbulence has vastly improved in recent decades, it can be tough to predict. 

“You’re talking about a little pin drop in the atmosphere,” says Bill Duncan, head of aviation forecasting operations at the Weather Co., which supplies turbulence forecasts and weather insights to major airlines. 

Turbulence happens when swirling air currents push against the wing of the plane, which then moves the wings up and down or the body of the plane from side to side, says Paul D. Williams, a professor of atmospheric science at the University of Reading in England. 

Projected average percentage change of moderate

clear-air turbulence from preindustrial times to 2050–2080, for September, October and November

Source: Paul D. Williams, University of Reading
Emma Brown/THE WALL STREET JOURNAL

Atmospheric pressure, changing wind direction, air around mountains and cold- or warm-weather fronts can cause turbulence, physicists say.

Turbulence caused by wind shear, meaning sudden changes in the speed and direction of wind, is called clear-air turbulence. It is called this because it occurs at higher altitudes in cloudless areas. Aircraft can change altitude suddenly, and pilots usually can’t detect this type of turbulence in advance.

Since 1979, the amount of wind shear in the jet stream has increased 15%, according to a study Dr. Williams co-wrote that was published in the science journal Nature in 2019. At higher altitudes where planes fly, climate change is altering temperature patterns, which creates more wind shear, he says.

What is Clear-Air Turbulence?

Clear-air turbulence often happens unexpectedly and without visual warning for pilots. This type of turbulence is caused by sudden changes in wind speed or direction, known as wind shear. 

Photo for illustration: Bettmann Archive/Getty Images

Sources: Federal Aviation Administration; Paul D. Williams, University of Reading

Dr. Williams’s research predicts that the amount of clear-air turbulence in the atmosphere in the mid-Northern Hemisphere is expected to more than double over the next three to six decades.  

Some of the more popular international flight routes from the U.S., such as New York-London and San Francisco-Tokyo, will experience more clear-air turbulence because they fly in the mid-Northern Hemisphere, he says.

Changes in procedure

Flight crews now use more specific language to address different levels of turbulence, says Dennis Tajer, a captain for American Airlines and spokesman for the Allied Pilots Association, a union. He began flying for commercial airlines about 30 years ago and says he encounters more clear-air turbulence now compared with early in his career.

American Airlines updated its flight manual in May 2022 to better define turbulence procedures for flight crews. The captain turns on the seat belt sign for all types of turbulence, but crews now take specific actions depending on the severity of the turbulence, he says.

During severe turbulence, flight attendants need to secure carts, place hot liquids in carts or on the floor and secure themselves as quickly as possible by sitting down in the nearest seat or on the floor.  

American and United are among the airlines that give pilots access to software called SkyPath, which crowdsources turbulence reports from pilots’ iPads in real time. 

SkyPath uses vibrations from the pilot’s iPad to measure turbulence and reports out to other nearby aircraft, providing advance warning of the conditions in real time, a United spokeswoman said in an email. 

Tips for navigating turbulence

• Wear your seat belt. Staying strapped in is the best way to protect yourself if your flight hits unexpected turbulence, pilots and flight attendants say. 
• Take precautions with children under 2. The FAA recommends passengers use an approved child-safety seat or device if traveling with a child under 2. Airlines don’t require children that young to have their own seats. Sara Nelson, the international president of the Association of Flight Attendants-CWA, and the union have renewed calls for all passengers to have their own seats. 
• Secure your electronics and other hand-held devices. Anything that isn’t tied down can become a projectile, Ms. Nelson says. 
• Remember the odds. Turbulence is scary because it is often unexpected and uncomfortable, says Todd Farchione, a clinical psychologist at Boston University’s Center for Anxiety and Related Disorders. Take a deep breath and realize you’re not truly in danger. Planes are built to withstand even heavy turbulence, pilots and physicists say.