Altitude plunge caused injuries on Singapore flight

Preliminary findings of an investigation into a Singapore Airlines flight hit by severe turbulence show a rapid change in gravitational force and a 54-metre altitude drop caused injuries.

A 73-year-old passenger died of a suspected heart attack and dozens were injured, including 12 Australians and a permanent resident, after flight SQ321, flying from London to Singapore, encountered what the airline described as sudden, extreme turbulence over Myanmar.

The May 21 flight on a Boeing 777-300ER plane carrying 211 passengers, including 56 Australians, and 18 crew diverted to Bangkok after the plane was buffeted by turbulence that flung passengers and crew around the cabin, slamming some into the ceiling.

"The aircraft experienced a rapid change in G (gravitational force) ... This likely resulted in the occupants who were not belted up to become airborne," the transport ministry said in a statement on the report by the Transport Safety Investigation Bureau.

"The vertical acceleration changed from negative 1.5G to positive 1.5G within four seconds.

Australian Keith Davis, a passenger on the Singapore Airlines
Injured Australian Keith Davis recalled the terrifying moment when the plane plunged. (AP PHOTO)

"This likely resulted in the occupants who were airborne to fall back down," it said, citing information extracted from the flight data and cockpit voice recorders.

"The rapid changes in G over the 4.6 seconds duration resulted in an altitude drop of 178ft (54m), from 37,362ft to 37,184ft. This sequence of events likely caused the injuries to the crew and passengers."

Shaken passengers described scenes of chaos in the minutes after the incident, with the turbulence throwing people upwards then into the aisle, many left with bleeding and head wounds.

Australian passenger Keith Davis recalled being throwing to the ceiling in "literally seconds" as the plane plunged, leaving him with cuts and bruising and his wife Kerry Jordan needing emergency spinal surgery.

Photographs of the cabin showed gashes in the overhead cabin panels, oxygen masks and panels hanging from the ceiling and luggage strewn around.

A passenger said some people's heads had slammed into lights above the seats and broken the panels.

Singapore Airlines said it acknowledged the report and was co-operating fully with the investigation.

"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," it said in a statement on Wednesday.

The airline late on Tuesday had said 42 people who were on board the flight were still in Bangkok, including 26 passengers receiving medical treatment in hospital.

Among those initially hospitalised were patients with spinal cord injuries and some with brain and skull injuries, according to Thai medical officials.

The preliminary report said that upon the flight encountering slight vibrations there was an uncommanded increase in altitude, resulting in the autopilot pitching the aircraft downwards.

The pilots experienced an increase in airspeed and responded by applying speed brakes.

"While managing the airspeed ... it was heard that a pilot called out that the fasten seat belt sign had been switched on," it said.

The investigation team comprised Singaporean investigators, representatives from Boeing and United States officials from the National Transportation Safety Board and the Federal Aviation Administration.

The Singapore transport ministry said the probe was ongoing.

AP with AAP