KUALA LUMPUR, Malaysia (NEWSnet/AP) — Investigators have found evidence of both a rapid change in gravitational force and a fast altitude drop during their research into turbulence on a Singapore Airlines flight May 21.

A 73-year-old British man died of a suspected heart attack and dozens more were injured during the flight on the Boeing 777, which was en route from London’s Heathrow airport to Singapore on May 21.

The plane, with 211 passengers and 18 crew members, then made an emergency landing in Bangkok.

Singapore’s Transport Ministry has finished its preliminary investigation and issued a report Wednesday. Their investigators, including those from the U.S. National Transportation Safety Board, Federal Aviation Administration and Boeing, had compiled a chronology of events based on the preliminary analysis of the flight’s data and cockpit voice recorders.

Early findings showed the aircraft was passing over the south of Myanmar at 37,000 feet when it began to experience vibration due to changes in the gravitational force, the ministry said. The plane then climbed to an altitude of up to 37,362 feet and increased speed possibly due to an updraft, it said. The plane’s autopilot then sought to pitch the jet downwards to its earlier altitude.

“The aircraft experienced a rapid change in G (gravitational force) ... this likely resulted in the occupants who were not belted up to become airborne” before falling back down later as the plane rose and fell, the ministry said. “The rapid changes in G over the 4.6 second duration resulted in an altitude drop of 178 feet ... this sequence of events likely caused the injuries to the crew and passengers.”

During the turbulence, it said a pilot was heard calling out saying the fasten seat belt sign had been switched on. It said recorded data indicated the pilots manually controlled the plane for 21 seconds to stabilize it before reengaging the autopilot.

The plane made a normal, controlled descent and didn’t encounter further turbulence until it landed in Bangkok almost an hour later, the ministry said, adding that investigations are ongoing.

Passengers have described the “sheer terror” of the aircraft shuddering, loose items flying and injured people fallen on the floor of the plane.

Twenty-six people remained hospitalized in Bangkok on Wednesday. Hospital authorities earlier said injuries included spinal or spinal cord damage, skull or brain injuries and damage to bones or internal organs.

It was unclear via this report what caused the turbulence. Most people associate turbulence with heavy storms, but the most dangerous type is so-called clear air turbulence.

Wind shear can occur in wispy cirrus clouds or even in clear air near thunderstorms, as differences in temperature and pressure create powerful currents of fast-moving air.

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