• A Delta flight encountered severe turbulence last year, with 17 people injured.
• The NTSB's newly published report says none of the injured people were wearing seatbelts.
• One passenger fractured four vertebrae and was hospitalized for over a month.

Newly released details from a 2023 incident that injured 17 airline passengers highlight the dangers of encountering turbulence, and serve as a stark reminder of why keeping your seatbelt on is always a good idea.

A Delta Air Lines Airbus A350 was flying from Milan to Atlanta when it encountered severe turbulence around 40 minutes from landing.

The National Transportation Safety Board made public its investigation last Friday. It found none of the injured people were wearing seatbelts despite the seatbelt sign being on.

10 of those who were injured were flight attendants, two of whom had serious injuries.

The flight's first officer told investigators that he told the cabin crew they should be seated due to expected turbulence. A list of injuries, shared with Delta and the NTSB, said the injured crew members weren't seated at the time.

One of those who was seriously injured suffered two broken ribs and back compression fractures, while the other had compression fractures in their neck and upper back, it said.

The other injuries to flight attendants included muscle strains, a concussion, and a deep cut that required stitches.

Five of the flight attendants were taken to hospital and released within 24 hours.

Of the seven passengers who were injured, one remained in hospital nearly a month after the flight. The person fractured four vertebrae and a rib, according to the NTSB report.

Another seriously injured passenger fractured one vertebra, while the others had muscle strains — mostly in the neck.

None of the injured passengers were wearing a seatbelt, the report said.

One of those passengers reported that her head hit the ceiling, hurting her neck, back, and head, although she was later able to walk off the plane.

Guy Gratton, an associate professor of aviation and the environment at Cranfield University, previously told Business Insider that a plane encountering turbulence is like "taking a box with something in it and starting to shake the box up and down."

"And clearly, if you're the person who's inside the box, then you get thrown around inside the box, and that's where injuries happen," he added.

"Passengers are told to keep their seatbelts done up because if you're tied to the box, you're much less likely to get injured."

While the Delta incident saw four serious injuries, cases of major injuries during turbulence are rare.

Between 2009 and 2023, 184 people were seriously injured by turbulence — an average of 12 a year — according to data from the Federal Aviation Administration. The majority of those, 146, were flight attendants rather than passengers.

• Southwest Airlines is reportedly set to end cabin service earlier in a bid to reduce flight attendant injuries.
• The change would see cabin landing preparations begin at 18,000 feet rather than 10,000 feet.
• It comes amid increasing reports of turbulence-related injuries.

Southwest Airlines is reportedly set to end cabin service earlier from December 4 in a move designed to help prevent injuries to its flight attendants.

Flight attendants will begin landing preparations at 18,000 feet rather than 10,000 feet going forward, the company said in an internal memo seen by View From the Wing.

The memo said that an evaluation of data from reports by pilots and flight attendants and information from the Flight Data Analysis Program suggested that seating staff sooner should reduce injuries by at least 20%.

"If we do not achieve the desired result, we will continue to find solutions," the memo said. "We are also committed to sharing updates on these findings periodically."

For passengers, the change means the usual pre-landing checklist — carry-on luggage stowed, window shades up, and seats and tables upright — will need to be completed sooner.

The memo says pilots will announce the beginning of the descent phase to the cabin before making a chime at 18,000 feet to signal the start of the sterile flight deck — a period when flight crew members should not be disturbed except for emergencies.

"This chime serves as your cue to secure the cabin for landing and to be seated and secured in your jumpseats," it says.

The World Economic Forum has said that from 2009 to 2023, 37 passengers and 146 crew members were seriously injured as a result of turbulence.

In May, a 73-year-old passenger died on board a Singapore Airlines flight when the plane dropped 178 feet in around four seconds.

Although serious turbulence-related injuries are rare, turbulence appears to be getting more common and increasingly severe.

Southwest Airlines did not immediately respond to Business a request for comment from Business Insider.

• An American Airlines flight returned to São Paulo after turbulence injured a passenger.
• The airline said there were more than 200 people on board, and the seatbelt sign was on.
• Several carriers have changed protocols because of rising concerns about turbulence.

An American Airlines passenger was taken to hospital after their flight encountered turbulence.

Data from Flightradar24 shows that Saturday's Flight 930 from São Paulo to Miami U-turned less than two hours after taking off. It ultimately became a 4 ½-hour flight to nowhere.

An airline spokesperson confirmed to Business Insider that the flight landed safely back in São Paulo "after encountering turbulence while in flight."

"We thank our crew members for their professionalism and our customers for their understanding," they added.

The Boeing 777 had 12 crew members and 221 passengers, one of whom was taken to a hospital in Brazil, according to the airline. The airline also said the seatbelt sign was on when the plane encountered turbulence.

The Aviation Herald, which first reported the incident, said the passenger had a fractured leg, while some others had minor injuries.

Many airlines changed their protocols this year because of rising incidents involving heavy turbulence.

A Singapore Airlines passenger died and dozens more were injured during severe turbulence in May. The airline then announced it would no longer serve meals when the seatbelt sign was on.

It was followed by a change in protocol at Korean Air, which decided to end its cabin service early and stop serving instant noodles to economy passengers.

Korean Air said turbulence had "become a persistent and growing problem in recent years." It added that the number of incidents had doubled in the first quarter of this year compared with the same period in 2019.

It also suggested the climate crisis had had an impact, citing "large temperature differences between altitudes."

Turbulence is created when differences in wind speed result in more friction between air molecules. A warmer climate imparts more energy into the air, which in turn creates more friction.

This is especially notable around the jet streams, where clear-air turbulence is most prevalent.

In a 2023 study, researchers from the University of Reading found that at a typical point over the North Atlantic, the most severe type of clear-air turbulence increased by 55% between 1979 and 2020.