The Transport Safety Investigations Bureau of Singapore (TSIB) has released their preliminary findings for the SQ321 flight incident after retrieving data from the flight data and cockpit voice recorder from the plane less than a week ago.
A media release by the Ministry of Transport on May 29, 2024, listed a summary of the events that happened aboard according to TSIB's investigations.
What happened
According to the release, SQ321 departed London on May 20, and the flight was normal prior to the turbulence event. All times noted are in Coordinated Universal Time (UTC).
At 7:49:21am on May 21, the aircraft was passing over the south of Myanmar at 37,000 ft and "likely flying over an area of developing convective activity".
The gravitational force (G), recorded as vertical accelerations, "fluctuated between positive (+ve) 0.44G and +ve 1.57G for a period of about 19 sec", causing "slight vibration".
Around the same time as the onset of the "slight vibration", an "uncommanded increase" in aircraft altitude, reaching a peak of 37,362ft, was recorded.
In response to this "uncommanded" altitude increase, the autopilot pitched the aircraft downwards to descend back to an altitude of 37,000ft.
The pilots observed an "uncommanded" increase in airspeed, which they responded to by extending the speed brakes.
TSIB believed both the "uncommanded" increase in altitude and airspeed mentioned were most likely due to the aircraft being acted upon by an updraft, which is the upward movement of air.
A rapid descent
At 7:49:32am, as both pilots were managing the airspeed, a pilot called out for passengers to fasten their seat belts.
Just eight seconds later, at 7:49:40am, the aircraft experienced a rapid change in G-force "from +ve 1.35G to negative (-ve) 1.5G" within just 0.6 seconds.
TSIB said it likely caused those not wearing their seatbelts to become airborne.
One second later at 7:49:41am, the vertical acceleration reversed from -ve 1.5G to +ve 1.5G within 4 seconds. This likely resulted in the occupants who were airborne to fall back down.
The rapid fluctuations in G-force over the 4.6-second duration resulted in an altitude drop of 178 ft (54.3m), from 37,362ft to 37,184ft.
54.3m is the equivalent of 20 floors in an HDB block.
TSIB believes that this sequence of events likely caused the injuries to the crew and passengers.
Amid the rapid changes in G-force, pilots initiated control inputs to stabilise the aircraft, disengaging the autopilot in this process.
The pilots then manually controlled the aircraft for 21 seconds and reengaged the autopilot at 07:50:05am.
Gradual fluctuations in G were recorded for the next 24 seconds, while the aircraft returned to 37,000ft at 07:50:23 hr.
Diverted to Bangkok
After the turbulence event, the pilots decided to divert to Suvarnabhumi Airport, Bangkok, Thailand, after the cabin crew informed them that there were injured passengers.
On the way to Bangkok, the pilots requested medical services to meet the aircraft on arrival.
Approximately 17 minutes after the turbulence event, at 8:06:51am, the pilots initiated a normal, controlled descent from 37,000ft and the aircraft reached 31,000ft at 8:10:00am.
The data showed that the aircraft did not encounter further severe turbulence during this diversion, and touched down in Suvarnabhumi Airport at 8:45:12am.
TSIB said investigations are ongoing.
Statement from SIA
SIA issued a statement on the preliminary findings by TSIB.
SIA said that it is "fully cooperating with the relevant authorities in the ongoing investigations into this incident" and that "the safety and well-being of our passengers and staff are our top priorities."
SIA added that it is "committed to supporting our passengers and crew members who were on board SQ321 on that day, as well as their families and loved ones." This includes "covering their medical and hospital expenses, as well as any additional assistance they may need."
SIA also expressed its appreciation for 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."
"We are also humbled by and grateful for the encouragement from our passengers and members of the public," SIA said.
Top photos from Thairath