A SUDDEN 54-METRE altitude drop caused unbelted passengers on a Singapore Airlines flight hit by deadly turbulence to be thrown violently inside the cabin, said Singapore’s transport ministry in a statement today.

One person died and several other passengers and crew onboard the flight from London suffered skull, brain and spine injuries during last week’s terrifying high-altitude ordeal.

The pilots diverted the Singapore-bound Boeing 777-300ER carrying 211 passengers and 18 crew to Bangkok, where the injured were taken to hospitals.

Singapore Airlines today said that 42 passengers from the flight were still in Bangkok, including 26 in hospital, and that the airline is cooperating in the ongoing investigation.

‘Rapid change’

In a statement today, the Singapore transport ministry said the aircraft experienced a “rapid change” in gravitational force, or G-force, while the plane was passing over the south of Myanmar, citing a preliminary report by Singapore’s Transport Safety Investigation Bureau.

The ministry said that “vertical acceleration” decreased from positive 1.35 G-force to negative 1.5 G-force within 0.6 seconds.

It is said this likely resulted in “the occupants who were not belted up to become airborne”.

Vertical acceleration again changed from negative 1.5G-force to positive 1.5G-force within four seconds and “this likely resulted in the occupants who were airborne to fall back down”, it added.

“The rapid changes in Gravitational force over the 4.6 second duration resulted in an altitude drop of 178 ft, from 37,362 ft to 37,184 ft,” according to the statement.

“This sequence of events likely caused the injuries to the crew and passengers.”

The transport ministry said the early report was based on data taken from the plane’s flight data recorder and cockpit voice recorder.

The investigation team included experts from Singapore’s Transport Safety Investigation Bureau, as well as the US National Transportation Safety Board, the US Federal Aviation Administration and the plane’s manufacturer Boeing.

The plane initially experienced slight vibration which resulted in an “uncommanded increase in aircraft altitude” from 37,000 feet to 37,362 feet before the autopilot pitched the plane downward to its original altitude.

The pilots also observed an “uncommanded increase in airspeed” which they slowed.

While managing the speed, a pilot was heard calling out that the fasten-seat-belt sign had been turned on, according to the ministry.

The “uncommanded” increases in altitude and airspeed were most likely caused by an “updraft”, or the upward movement of air, it said.

The ministry statement did not mention the plane plunging 1,800 metres (6,000 feet) in just a few minutes, which was shown on flight tracking data.

Clear air turbulence has become more common in the last 40 years, according to some scientific research which points to climate change as a possible factor.

But there are also more planes in the skies than ever before, which could also contribute to the increase in related incidents.

A flight safety expert told The Journal that passengers should keep their seatbelt on for the duration of a flight, whether or not the overhead light is switched on.

Micheal Comyn said people tend to be complacent about fastening their seat belts mid-flight and this can result in injuries when a plane hits a patch of clear turbulence which can’t be detected by radar.

“If they don’t follow the safety instructions and they don’t have their seatbelts on, in exactly the same way if you went over a humpback bridge on a double-decker bus, you’d hit the ceiling, too,” said Comyn.

He also advised people to pay attention to the pre-flight safety demonstration and added: “You have a 40% higher chance of surviving a survivable accident if you paid attention that day to the demonstration.”

- © AFP 2024 and with additional reporting from David MacRedmond