The Singapore Airlines flight that encountered severe turbulence on its way from London to Singapore dropped 54 meters in less than five seconds, preliminary findings released Wednesday showed.

The Transport Safety Investigation Bureau of Singapore said the sharp altitude drop as well as changes to gravitational forces likely caused the injuries. One person died of a suspected heart attack, and many of the 211 passengers and 18 crew members onboard were injured in the incident on May 21.

“The rapid changes in G [gravitational force] over the 4.6 sec duration resulted in an altitude drop of 178 ft, from 37,362 ft to 37,184 ft. This sequence of events likely caused the injuries to the crew and passengers,” the report said Wednesday.

The changes in gravitational forces “likely resulted in the occupants who were not belted up to become airborne,” the report said. They then almost immediately fell back down as vertical acceleration turned negative, it added.

Pilots engaged controls in an attempt to stabilize the aircraft while gravitational forces were fluctuating, according to the report, which is based on flight data recorder and cockpit voice recorder data. It also said that seatbelt fastening signals were switched on as the incident unfolded.

Following the incident on flight SQ321, the flight diverted to Bangkok’s Suvarnabhumi Airport, where it was received by medical services.

At the time of the incident, the aircraft was over Myanmar, “likely flying over an area of developing convective activity,” according to the report. Convective activity is linked to temperature shifts in the air, which can cause currents that lead to turbulence.

Turbulence-related incidents are the most common type of accident commercial airlines experience, according to the U.S. National Transportation Safety Board, but severe injuries are rare.

In a statement shared on social media, Singapore Airlines said it had acknowledged the findings of the investigation and that it was cooperating on it with relevant authorities.

“The safety and well-being of our passengers and staff are our top priorities,” the airline said.

“We are committed to supporting our passengers and crew members who were on board SQ321 on that day, as well as their families and loved ones. This includes covering their medical and hospital expenses, as well as any additional assistance they may need.”

Following the incident, Singapore Airlines said it had adapted its seatbelt policy to a “more cautious approach” to turbulence. This included no longer running hot drink and meal services when seatbelt signs are switched on.

Flight data also showed that journeys between London and Singapore had taken a slightly different route since the incident, avoiding the area where it occurred.