Turbulence remains a major cause of injuries to flight passengers and crew, even as U.S. airlines have made steady improvements in their overall accident rate in recent years.

A Lufthansa flight from Texas to Germany is the latest example. The Airbus A330 reported severe turbulence over Tennessee on Wednesday and was diverted to Virginia’s Washington Dulles International Airport. Seven people were taken to hospitals with injuries believed to be minor.

Climate change is expected to make turbulence worse in the coming decades, experts say, though improvements in weather forecasting will help.

Turbulence accounted for 37.6% of all accidents on larger commercial airlines between 2009 and 2018, according to a 2021 report from the National Transportation Safety Board. The Federal Aviation Administration released data last year showing 146 serious injuries resulted from turbulence from 2009 to 2021.

Last year, over the span of two days in December, a flight to Honolulu and a flight to Houston hurt a total of 41 people. In July, severe turbulence led to at least eight minor injuries on a flight to Nashville, Tennessee, that had to be diverted to Alabama. Also, three separate flights to Detroit, Miami and Columbus, Ohio, resulted in series injures to three crew members, according to NTSB data.

The NSTB has said more can be done — both within the industry and among passengers — to limit injuries from turbulence. And everyone agrees that simply wearing a seatbelt during the entire flight will significantly reduce one’s risk of getting hurt.

WHAT IS TURBULENCE?

Turbulence is essentially unstable air that moves in a non-predictable fashion. Most people associate it with heavy storms. But the most dangerous type is clear-air turbulence, which often occurs with no visible warning in the sky ahead.

Clear-air turbulence happens most often in or near the high-altitude rivers of air called jet streams. The culprit is wind shear, which is when two huge air masses close to each other move at different speeds. If the difference in speed is big enough, the atmosphere can’t handle the strain, and it breaks into turbulent patterns like eddies in water.

“When those eddies are on the same scale as the aircraft, it causes one side of the aircraft to go up and one side to go down or causes the airplane to lose and gain altitude very quickly,” said Thomas Guinn, a meteorology professor at the Embry-Riddle Aeronautical University in Daytona Beach, Florida.

If pilots experience moderate turbulence, they can generally avoid it by flying to a higher altitude, Guinn said. But severe turbulence needs to be avoided all together.

“We can give kind of broad areas of where the turbulence is,” Guinn said. “If the indicators are for severe, then we generally expect pilots to to avoid those regions.”

WHAT ROLE DOES CLIMATE CHANGE PLAY?

Paul D. Williams, a professor of atmospheric science at the University of Reading in England, says global warming is changing temperature patterns in the upper atmosphere. That is causing more instability in the jet streams.

“More specifically, at flight-cruising altitudes, the tropics are warming more rapidly than the poles … leading to stronger north-south temperature differences across the jet stream, and it is those temperature differences that drive the wind shear,” Williams wrote in an email.

But the implications for air travelers are still not fully known, he cautioned.

“One could argue that pilots should be getting better at avoiding turbulence over time, because the specialized forecasts that are used to seek out smooth routes are gradually improving,” Williams wrote. “So more turbulence in the atmosphere will not necessarily translate into more injuries.”

HOW COMMON ARE TURBULENCE-RELATED INJURIES?

The NTSB’s 2021 report showed that 111 turbulence-related accidents occurred between 2009 and 2018 that resulted in at least one serious injury. That figure applies to commercial carrier planes with more than nine passenger seats.

“Most passengers seriously injured … are either out of their seats or seated with their seat belts unfastened,” the report said.

Flight attendants — who are often up and moving — were most commonly hurt, accounting for 78.9% of those seriously injured.

Numbers released by the FAA in December showed a similar breakdown between 2009 and 2021: 116 of the 146 serious turbulence injuries — or 79% — were among crew.

Accident reports filed with the NTSB provide examples. For instance, turbulence on a flight from Dallas-Fort Worth to Miami in July 2021 resulted in a flight attendant “striking the floor hard” in the aft galley and being diagnosed with “a fractured compressed vertebra.”

On another flight from San Antonio to Chicago in August 2021, a flight attendant “had fallen to her knees because of the turbulence” and “was diagnosed with a fractured kneecap.” And on a flight from Baltimore to Atlanta in October 2021, a flight attendant fell and broke her ankle during drink service when the plane “unexpectedly entered a cloud and experienced moderate to borderline severe turbulence.”

“When turbulence occurs, it can be severe and lead to significant, very serious injuries: everything from broken bones to spinal issues to neck issues,” NTSB Chair Jennifer L. Homendy said in a December interview.

WHAT CAN BE DONE?

The NTSB’s 2021 report offered a long list of recommendations. They included more information-sharing among pilots, carriers and air traffic controllers regarding the weather and turbulence incidents.

“We want to make sure that the best suite of technologies is used … to provide the best information to pilots and flight attendants and passengers,” Homendy told The Associated Press.

The agency also urged revisions to safety recommendations regarding when flight attendants should be secured in their seats, including additional portions of descent, which would “reduce the rate of flight attendant injuries.”

The report also cited parents who have been unable to hold infants securely on their laps during turbulence. The NTSB stated that it’s safest for children under the age of 2 to be in their own seat and using an appropriate child restraint system.

Michael Canders, director of the Aviation Center at Farmingdale State College in New York, said many in the industry are already sharing information with each other regarding turbulence, while forecasting has improved over the years.

But he’s unconvinced that it will ever be perfect.

“There’s this argument or debate about, ‘Will technology save us or do we need to back off and take better care of the earth?’” said Canders, who is also an associate professor of aviation. “I think we have to do both.”

Canders added that preventing injuries from turbulence is “best addressed by sitting in your seat and seat-belting in.”