A Delta Air Lines flight from Salt Lake City to Amsterdam was rocked by violent turbulence on July 30, leaving more than a dozen people injured, according to a preliminary report from the National Transportation Safety Board (NTSB).

Delta Flight 56, an Airbus A330 with 275 passengers and 13 crew members on board, was cruising near Creston, Wyoming, when the turbulence struck without warning. The seat belt sign was off, and meal service was underway when passengers, flight attendants, and service carts were suddenly thrown toward the ceiling.

The NTSB said the violent shaking lasted about 2.5 minutes. During that time, the aircraft exceeded its maximum allowable speed, disengaged the autopilot, and jolted through three rapid climbs and descents. G-forces spiked to 1.75 before plunging into negative gravity, which sent unbelted passengers slamming into the plane’s interior.

“Preliminary flight data recorder information revealed that the upset lasted approximately 2.5 minutes,” the NTSB report stated.

The turbulence came even though forecasters had flagged southwestern Wyoming as a potential trouble spot earlier in the day. At 35,000 feet, however, pilots reported seeing only “light cirrus clouds,” and their iPad forecasts suggested minimal risk.

Twenty-five people, including seven crew members, were taken to hospitals after the plane diverted for an emergency landing in Minneapolis. Two people sustained serious injuries, while five others suffered minor injuries. The turbulence also caused minor cabin damage and scattered food, drinks, and service equipment across the aisles.

An off-duty first officer walked through the cabin to assess the situation, while a passenger who was a physician assistant provided triage for the injured crew. After reporting back to the cockpit, the crew declared an emergency and diverted safely.

The NTSB said its investigation remains ongoing, with flight data and cockpit voice recorders being analyzed in Washington, D.C. A final report, including the probable cause of the incident, is expected within 12 to 18 months.