Overview
On July 30, 2025, at 1723 mountain daylight time, Delta Air Lines Flight 56, an Airbus A330-941, experienced severe turbulence while cruising at 37,000 feet near Creston, Wyoming. The aircraft was operating under Title 14 Code of Federal Regulations Part 121 as a scheduled international passenger flight from Salt Lake City International Airport (KSLC), Utah, to Amsterdam Airport Schiphol (EHAM), Netherlands. After the turbulence, the flight crew diverted to Minneapolis-St Paul International Airport (MSP), Minnesota.
Flight Crew Actions Before the Event
Prior to departure, the flight crew discussed weather along the route, expecting some turbulence during climb over the mountains east of Salt Lake City. They planned to deviate after crossing the mountains. The departure was smooth until reaching the Wasatch Mountains, where light turbulence occurred. As the aircraft passed through flight level (FL) 300, the ride smoothed enough for cabin crew to begin service. At FL350, where they remained for about five minutes due to traffic, the turbulence forecast on their electronic flight bag displayed green conditions, and they observed only light cirrus clouds. The captain then turned off the seatbelt sign.
As the climb continued to FL370, the crew noticed 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 this heading would keep them above the cloud deck, upwind of the buildups, and they had received no adverse ride reports. After scanning the horizon and weather radar, noting returns of concern 40–50 miles away, they accepted the left turn.
Turbulence Encounter
After completing the turn, the aircraft experienced an overspeed event, exceeding the maximum operating speed by about 15–20 knots. An updraft carried the aircraft to FL380 over approximately 20 seconds, during which the autopilot disengaged. Shortly thereafter, the aircraft descended rapidly to FL355, and a cycle of climbs and descents repeated about three times over two to three minutes, leading the aircraft back into a cloud layer. The first officer, who was the pilot flying, initiated the All Attitude Upset Recovery Strategy procedure at least once before recovering and re-engaging the autopilot.
Preliminary flight data recorder information indicated the upset lasted about 2.5 minutes. Vertical acceleration oscillated between a maximum positive peak of 1.75 g and a minimum negative peak of -0.5 g. Pitch angle ranged from about 5° nose down to 10° nose up, and roll angle varied from about 40° left wing down to 5° right wing down. Computed airspeed fluctuated between about 230 knots and 290 knots. A convective Significant Meteorological Information (SIGMET) warning of thunderstorms with cloud tops above FL450 was in effect for the time and area.
Aftermath
After the event, the captain divided cockpit duties. The pilot flying 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 assisted the cabin crew with triage. After the relief first officer returned to the flight deck, the crew planned a diversion and declared an emergency with ATC. They diverted to MSP to avoid weather, reviewing overweight landing performance data and suitable runways. After landing, they noticed hot brakes on the right main landing gear and notified ground personnel. The aircraft taxied to the gate, where airport rescue firefighting, medical, and maintenance personnel met them.
Investigation
The NTSB invited qualified parties to participate in the investigation, including the Federal Aviation Administration, Delta Air Lines, the Air Line Pilots Association, and the Professional Airline Flight Controllers Association. An Accredited Representative from the Bureau d'Enquêtes et d'Analyses of France, the state of manufacture, was appointed to support the investigation, with Airbus and the European Union Aviation Safety Agency as technical advisors. Flight data and cockpit voice recorders were sent to the NTSB Vehicle Recorder Laboratory in Washington, D.C. NTSB specialists in cockpit voice recorder, flight data recorder, meteorology, air traffic control, and operational factors were assigned. The investigation is ongoing.