Injuries to SQ321 crew, passengers likely caused by rapid changes in G-force, 178ft drop over 4.6sec

SIA acknowledged the preliminary findings and said it is fully cooperating with the authorities in the ongoing investigations. - Reuters

SINGAPORE: A rapid change in gravitational forces (G-forces) over 4.6 seconds resulted in an altitude drop of 178 feet by Singapore Airlines flight SQ321, which likely caused the injuries to crew and passengers, according to the findings of a preliminary investigation.

This is according to the initial report issued by investigators from the Transport Safety Investigation Bureau (TSIB) on Wednesday (May 29), based on a preliminary analysis using the data stored in the flight data recorder and cockpit voice recorder on board the aircraft.

The TSIB is the air, marine and rail accidents and incidents investigation authority in Singapore and is part of the Ministry of Transport.

The investigation team comprised TSIB investigators and representatives from the United States’ National Transportation Safety Board, Federal Aviation Administration and aircraft manufacturer Boeing.

Investigators found that the aircraft, a Boeing 777-300ER, was flying at its cruise altitude of 37,000ft south of Myanmar and near an area of developing storms at 3.49.21pm Singapore time in the afternoon, when turbulence started to cause fluctuations between +0.44g and +1.57g for 19 seconds.

G-forces measure the rapid acceleration or deceleration by comparing it with the normal pull of gravity on earth, which is considered +1g. Hence, at +1.57g, a person would feel like they were 1.57 times their body weight.

On board SQ321, the passengers would also start to feel the plane beginning to vibrate slightly. The aircraft started to climb, reaching 37,362ft in altitude.

It was at this point that the plane’s autopilot tried to bring the plane down to its set cruise altitude, with the pilots turning on the seat belt sign at 3.49.32pm.

Eight seconds later, the plane experienced a rapid change in G-forces from +1.35g to -1.5g within 0.6 seconds. Negative G-forces move opposite to the direction of gravity, causing people to experience a sensation of “lightness” or “floating”.

In SQ321’s case, it caused the passengers and crew who did not manage to fasten their seat belts to become airborne, and at 3.49.41pm the G-forces went from -1.5g back again to +1.5g in four seconds.

This caused the aircraft to drop from 37,362ft to 37,184ft and all airborne passengers to fall back down, likely injuring dozens of passengers and one to suffer a fatal heart attack.

During this time, the pilots tried to retain control of the aircraft in a bid to stabilise it, disengaging the autopilot in the process, before re-engaging it and starting a descent to divert into Bangkok’s Suvarnabhumi Airport, landing at 4.45pm that afternoon.

In a statement on May 29, SIA acknowledged the preliminary findings from TSIB and said it is fully cooperating with the authorities in the ongoing investigations.

The airline said it is committed to supporting the passengers and crew members on board SQ321, including covering their medical and hospital expenses, as well as any additional help they may need.

“We deeply appreciate the invaluable assistance provided by the governments of Singapore and Thailand, as well as our many partners and the medical teams in both countries and around the world,” SIA said.

The airline said 26 passengers from SQ321 are still hospitalised in Bangkok as of 5.30pm on May 29. - The Straits Times/ANN

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