N422DZ

On July 30, 2025, at 1723 mountain daylight time, Delta Air Lines flight 56, an Airbus A330-941, encountered severe turbulence while in cruise flight at an altitude of 37,000 ft near Creston, Wyoming. After determining that injuries had occurred, the flight crew diverted to Minneapolis-St Paul International airport (MSP), Minneapolis, Minnesota. After landing, 24 of the 246 passengers were evaluated by emergency medical technicians, with 18 transported to local hospitals for additional assessment; information regarding their conditions is currently unavailable. Of the 10 cabin crew members, 2 sustained serious injuries, 5 sustained minor injuries, and 3 were uninjured. None of the 3 flight crew members were injured. The airplane sustained minor damage to interior components. The airplane was operating under the provisions of Title 14 Code of Federal Regulations (CFR) Part 121 as a scheduled international passenger flight from Salt Lake City International Airport (KSLC), Salt Lake City, Utah, to Amsterdam Airport Schiphol (EHAM) in Haarlemmermeer, Netherlands. According to the flight crew, prior to departure they had discussed the conditions along the route, noting that they could expect some weather during the climb, and that turbulence was predicted over the mountains east of SLC. They anticipated deviating after crossing the mountains. The departure was relatively smooth, until they reached the Wasatch Mountains, where they experienced some turbulence. As they passed through flight level (FL) 300, the ride had smoothed out enough to allow the cabin crew to begin service. At FL350, where they remained for about 5 minutes due to traffic, they noted that the turbulence predicted on their electronic flight bag weather application was “in the green” and they had observed only light cirrus clouds. About this time the captain turned off the seatbelt sign. As the climb continued to FL370, they noticed some weather buildups and requested a right deviation from air traffic control (ATC). ATC suggested a left turn to a heading of 350°. The crew assessed that heading would keep them above the cloud deck, upwind of weather buildups, and they had not heard any adverse ride reports. After scanning the horizon and the weather radar, noting that the only returns of concern were 40-50 miles away, they accepted the left turn. After completing the turn, the airplane encountered an overspeed event (exceeding the maximum operating speed by about 15-20 knots), along with an updraft that carried it to FL380 over the course of about 20 seconds, during which the autopilot disengaged. Shortly thereafter, the airplane descended ‘rapidly’ to FL355, and a climb/descent cycle repeated about three times over a two- to three-minute period, which resulted in the airplane re-entering a cloud layer. The first officer who was the pilot flying (PF), initiated the All Attitude Upset Recovery Strategy procedure at least once during this time, before having recovered and re-engagedthe autopilot. A review of preliminary flight data recorder information revealed that the upset lasted approximately 2.5 minutes. During this time, the vertical acceleration oscillated, reaching a maximum positive peak of about 1.75 g and a minimum negative peak of about -0.5 g. The pitch angle also oscillated, ranging from a low of about 5° nose down to a high of about 10° nose up. Roll angle variations included a maximum of about 40° left wing down and about 5° right wing down. Computed airspeed fluctuated as well, with peaks ranging from about 230 knots to about 290 knots. A convective Significant Meteorological Information (SIGMET) was in effect for the time and area of the accident. It warned of thunderstorms moving from the southwest at 10 knots, with cloud tops above FL450. Figure 1 shows the airplane’s ground track and radar imagery from the National Weather Service at the time of the accident. Figure 1 - Ground Track and National Weather Service radar imagery at time of accident. After the event, the captain divided cockpit duties. The PF continued to fly and manage ATC communications, while the captain coordinated with the cabin crew and dispatch. The relief first officer, who had been in the crew rest bunk, walked through the cabin to assess injuries and gather information. A passenger who was a physician assistant aided the cabin crew with triage. After the relief first officer returned to the flight deck, the crew planned for a diversion and declared an emergency with ATC. They elected to divert to MSP to avoid weather and reviewed overweight landing performance data and suitable runways. After landing, they noticed that the right main landing gear brakes were hot and notified ground personnel. They taxied to the gate and were met by airport rescue firefighting, medical, and maintenance personnel. As part of the investigative process, the NTSB invited the qualified parties to participate in the investigation. These included the Federal Aviation Administration, Delta Air Lines, the Air Line Pilots Association, and the Professional Airline Flight Controllers Association. In accordance with the provisions of Annex 13 to the Convention on International Civil Aviation, an Accredited Representative from the Bureau d'Enquêtes et d'Analyses of France, the State of Manufacture for the airplane, was appointed to support the investigation with Airbus and the European Union Aviation Safety Agency as their technical advisors. The flight data and cockpit voice recorder data were sent to the NTSB Vehicle Recorder Laboratory in Washington, D.C. The following NTSB specialists were assigned to investigate the accident: Cockpit Voice Recorder, Flight Data Recorder, Meteorology, Air Traffic Control, and Operational Factors. The investigation is ongoing.