Singapore Airlines plane crashed 54 meters in 4.6 seconds

The Singapore Airlines flight that hit extreme turbulence last week was operating on autopilot when it experienced uncontrolled changes in altitude and speed, according to a preliminary investigation by the Transport Safety Investigation Bureau of Singapore released on Wednesday.

The London-Singapore flight plunged 170 feet (54 meters) in 4.6 seconds, causing unbelted passengers to be rapidly thrown into the air and fall back to the ground, “likely resulting in injuries to crew and passengers,” the report said.

The incident resulted in one death and dozens of injuries and is, according to aviation experts, one of the worst turbulence-related accidents of all time.

Singapore Airlines Flight 321 departed London on May 21 and was operating normally before encountering extreme turbulence while crossing the southern part of Myanmar at an altitude of 37,000 feet, after which the aircraft experienced slight vibrations.

At the same time, the plane “began to increase its altitude without being asked to do so,” after which the plane’s autopilot system reduced the altitude to the programmed 37,000 feet. The pilots said the plane also “increased speed without being asked to do so,” which they stopped by applying the plane’s airbrakes.

“Recorded data showed that the pilots initiated control inputs to stabilize the aircraft, disengaging the autopilot in the process,” the report said. The pilots controlled the aircraft manually for 21 seconds before re-engaging the autopilot.

While adjusting the speed of the aircraft, one of the pilots shouted that the fasten seatbelt sign was on, according to data stored in the flight data recorder and cockpit voice recorder, which formed the basis of the preliminary findings of the investigation.

Singapore’s Ministry of Transport conducted the investigation with assistance from the US National Transportation Safety Board (NTSB), the Federal Aviation Administration (FAA) and Boeing, which built the 777 aircraft flown by Singapore Airlines.

The aircraft’s sudden changes in altitude and speed caused rapid changes in G-forces over a period of 4.6 seconds, resulting in the extreme drop in altitude. After the turbulence subsided and the pilots were informed by the flight crew that several passengers were injured, the flight was diverted to Bangkok, Thailand.

About 17 minutes after the turbulence, the pilots began a “normal, controlled descent” and did not encounter further severe turbulence until landing, the report said.

Aviation experts said the rapid change in G-force would have hurled unbelted passengers against the cabin ceiling and pinned them there before being thrown to the ground with even greater force.

Almost half of the 229 people on board the flight received medical treatment after landing in Bangkok; 28 passengers are still in hospitals a week after the accident, according to Singapore Airlines.

The investigation into the incident is ongoing.