‘Rapid’ G-force changes and altitude drop in preliminary report linked to injuries on Flight SQ321

On 21 May, Singapore Airlines flight SQ321, travelling from London to Singapore, encountered severe turbulence over Myanmar, leading to a tragic incident where a 73-year-old British passenger died, and dozens were injured.

The Ministry of Transport (MOT) has since released preliminary findings from the Transport Safety Investigation Bureau (TSIB) on Wednesday (29 May), revealing startling details about the event.

The TSIB’s investigation has been comprehensive, involving not only local investigators but also international representatives from the U.S. National Transportation Safety Board (NTSB), Federal Aviation Administration (FAA), and Boeing.

The investigation team has “compiled a chronology of events based on preliminary analysis of the data from FDR and CVR,” highlighting several critical moments during the flight.

According to the MOT’s statement, SQ321 departed London on 20 May and was flying normally prior to the turbulence event.

At 07:49:21 hr (UTC) on 21 May 24, the aircraft was passing over the south of Myanmar at 37,000 ft and likely flying over an area of developing convective activity.

It was then noted that the flight data recorder and cockpit voice recorder from SQ321 indicated that the aircraft experienced rapid changes in gravitational force. The gravitational force (G) recorded as vertical accelerations, fluctuated between +0.44G and +1.57G for a period of about 19 seconds.

“The rapid changes in G over the 4.6 sec duration resulted in an altitude drop of 178 ft [54 metres], from 37,362 ft to 37,184 ft. This sequence of events likely caused the injuries to the crew and passengers,” said MOT.

An uncommanded altitude increase was observed shortly afterward, prompting the autopilot to pitch the aircraft downwards. This was complicated by an increase in airspeed, which the pilots managed by extending the speed brakes.

The most severe moment occurred at 07:49:40 UTC, when vertical acceleration shifted from a positive 1.35G to a negative 1.5G in less than a second, causing unbelted occupants to become airborne.

Seconds later, the force shifted back to positive, leading to their forceful return to their seats or the floor.

The MOT report detailed, “This likely resulted in the occupants who were airborne to fall back down.”

Amid these rapid changes, the pilots manually controlled the aircraft for 21 seconds before reengaging the autopilot.

The aircraft subsequently stabilized and returned to its original altitude of 37,000 feet.

Following the incident, the injured passengers were assessed by the cabin crew, leading to the decision to divert the plane to Bangkok’s Suvarnabhumi Airport, where medical services were requested upon arrival.

The investigation is ongoing, with contributions from the TSIB, the U.S. National Transportation Safety Board (NTSB), Federal Aviation Administration (FAA), and Boeing.

As of the latest update by SIA on 28 May, 28 people injured during the flight remain hospitalized in Bangkok.

Further details are expected as the investigation progresses.