Investigators reveal details about just how bad the deadly Singapore Airlines turbulence was

• A report on Singapore Airlines' deadly turbulence says the plane dropped 178 feet in four seconds.
• Investigators say g-force changes in the plane likely caused passengers to fly out of their seats.

The turbulence on the deadly Singapore Airlines flight last week was so severe that the plane dropped 178 feet in just four seconds, investigators say.

Officials from Singapore's Transport Safety Investigation Bureau released a report on Wednesday describing what happened on the May 20-21 flight from London to Singapore, where turbulence was so bad that it killed one passenger and injured over 100 other people.

The report details the plane's sudden catastrophic drop, one of the worst turbulence incidents in recent history.

It says that while flying over Myanmar, the plane most likely passed over an area developing bad weather, causing a "slight vibration" for about 20 seconds.

The report says an updraft likely caused uncontrolled increases in altitude and speed. In response, the autopilot — which remained engaged despite the drop — pulled the plane back down in an attempt to reach 37,000 feet. The pilots simultaneously applied speed brakes to reduce the airspeed, the report said.

The plane then experienced — in 4.6 seconds — a change from positive to negative gravitational force and back again, likely causing passengers who weren't wearing their seatbelts to fly out of their seats and then slam back down again, the report said.

Investigators found that during those few seconds, the plane fell 178 feet. The pilots reacted by disengaging the autopilot and manually stabilizing the aircraft for about 20 seconds before reengaging the autopilot, the report said.

The report said the entire incident, from slightly rough air to deadly turbulence, lasted one minute and two seconds.

In that short time, a 73-year-old British passenger was killed, and more than 100 other people on board were hurt, including several with paralysis, skull and back trauma, and brain injuries, The Associated Press reported.

Passengers have not said the seatbelt sign was on at the time of the incident, Forbes reported. However, investigators said audio from the cockpit voice recorder indicated "that a pilot called out that the fasten seat belt sign had been switched on."

The investigators' report said that when the pilots learned that passengers were injured, they diverted the flight to Bangkok. The flight didn't encounter more turbulence before landing safely.

Singapore's transportation bureau said it was still investigating the turbulence. Singapore Airlines did not immediately respond to a request for comment from Business Insider.