Severe turbulence injures 18 on Delta flight from Salt Lake City to Amsterdam, NTSB says

The National Transportation Safety Board said 18 passengers were taken to hospital after an Airbus A330 operated by Delta Air Lines hit severe turbulence that launched people and service carts into the cabin during a transatlantic flight from Salt Lake City to Amsterdam.

Delta Flight 56, with 246 passengers and 10 cabin crew, diverted to Minneapolis–St. Paul International Airport after the two-and-a-half-minute episode, according to a Sept. 9 NTSB report. Twenty-four passengers were assessed for injuries and 18 were transported to hospitals. Two of the cabin crew sustained serious injuries, five had minor injuries and three were uninjured. None of the three flight crew were injured. The report said the airplane sustained only minor interior damage.

The NTSB report said the pilots had discussed weather along the route before departure and expected some turbulence during the climb. The flight encountered turbulence near the Wasatch Mountains soon after takeoff, then the ride smoothed and cabin service resumed. At that point the seat belt sign was turned off.

As the aircraft climbed toward cruise, pilots observed weather build-up and requested a deviation from air traffic control. A left turn was suggested. After completing the turn, the airplane was moving faster than anticipated and encountered an updraft that disengaged the autopilot at about 37,000 feet, the report said. The airplane then pitched up and down in a cycle repeated three times as the first officer flying attempted to stabilize the aircraft and re-engage the autopilot, producing two and a half minutes of severe turbulence.

The NTSB said onboard data showed forces reached as high as 1.75 g, or 75 percent greater than normal gravity. Aviation safety consultant Jeff Guzzetti, speaking to The Associated Press, described that magnitude as the equivalent of a large person grabbing a passenger and pulling upward with all his strength, a force that can hurl an unrestrained person into the ceiling and then back down to the cabin floor.

Passengers described violent motion and objects being thrown around the cabin. "If you didn’t have your seat belt on, everyone that didn’t, they hit the ceiling, and then they fell to the ground," passenger Leann Clement-Nash told ABC News. "And the carts also hit the ceiling and fell to the ground and people were injured. It happened several times, so it was really scary." Another passenger, William Webster, told CNN he felt a centrifugal force that left him off his seat for about 30 seconds and saw a wine cart thrown into the air.

Delta said it is cooperating with the NTSB investigation and that its Delta Care Team was working with customers to support immediate needs. The airline said safety is its top priority.

The NTSB said investigators will examine flight crew decisions and whether the flight crew could have avoided the weather encounter, including whether it was appropriate to turn off the seat belt sign when cabin service resumed. The board will also evaluate aircraft systems performance and meteorological information available to the crew.

In-flight turbulence can occur without warning when an aircraft encounters convective activity or clear-air updrafts and downdrafts, and it can produce rapid changes in acceleration that pose hazards to unrestrained passengers and loose items. The preliminary NTSB report provides a timeline and data from the flight but does not draw conclusions about probable cause. Investigators will continue to gather and analyze data, interview crew and passengers, and review air traffic communications as part of the ongoing inquiry.