Inside SQ321: Key findings from Singapore's final investigation report
Investigators have released their final report to address questions about what caused the disaster.
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SINGAPORE: Two years after severe turbulence left one passenger dead and dozens injured on a Singapore Airlines (SIA) flight, investigators have released their final report, addressing key questions about what caused the disaster.
Flight SQ321, travelling from London to Singapore, was diverted to Bangkok so passengers and crew could receive medical treatment.
What caused the turbulence?
In the immediate aftermath, multiple analysts attributed the incident to clear-air turbulence – invisible pockets of air that can occur at high altitudes in clear skies, without warning and with no time for crew to alert passengers.
The Transport Safety Investigation Bureau (TSIB) report concluded otherwise. The turbulence was convectively induced, meaning it was associated with convective clouds and thunderstorms – generated by air movement into the storm, strong updrafts, downdrafts and outflow winds.
This type of turbulence can exist outside cloud and can be encountered several thousand feet above it, and up to 20 miles laterally. TSIB noted it is common year-round in the tropics when thunderstorms develop.
Investigations found groups of clouds near the point where severe turbulence struck. One cloud's top grew rapidly from about 27,500ft at 7.40am UTC to about 40,000ft within 10 minutes.
“The turbulence experienced by the aircraft was likely the result of this rapidly growing cloud which could cause significant vertical air movements such as updrafts and downdrafts,” the report said.
SIA estimated that SQ321 likely passed over fast-growing convective clouds and encountered an updraft with a velocity of about 8,000 to 9,000ft per minute. Boeing, using flight recorder data, estimated maximum vertical wind speeds at about 150ft per second – consistent with SIA's assessment.
Did the pilots know there was bad weather ahead?
Four other aircraft flying in the vicinity at the time reported widespread clouds with tops between 35,000ft and 50,000ft, visible on their weather radar systems. All four deviated from their planned routes, experiencing light to moderate turbulence during the deviations.
The SQ321 crew saw none of this. In the minutes before disaster struck, their navigational displays showed no bad weather, and visual checks indicated a clear flight path. The cockpit voice recorder captured no discussion of weather between the pilots.
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TSIB noted that the other four aircraft were not on the same flight path and their accounts described general weather conditions over Myanmar rather than the specific location where SQ321 encountered turbulence.
“The investigation team is unable to understand why the flight crew of the occurrence flight did not see the widespread clouds,” said TSIB.
Did SQ321’s weather radar fail?
Investigators believe the weather radar was detecting weather intermittently during the flight and said they cannot rule out the possibility that it failed to detect, or under-detected, bad weather ahead.
SIA said that across 29,000 Boeing 777 flights between May 2023 and July 2025, 12 cases of under-detection, four cases of over-detection and 20 cases of not detecting inclement weather were logged.
The SQ321 aircraft accounted for one of the non-detection cases and two of the under-detection cases. When the aircraft was flown back to Singapore from Bangkok after the incident, indications of under-detection also occurred.
Investigators concluded it was "likely" that the aircraft's weather radar did not detect bad weather before the turbulence struck.
But the radar manufacturer, which was not named in the report, said it found no evidence that the system had failed to detect and display weather during the flight.
Why were so many people injured?
The rapid and extreme changes in gravitational force were strong enough to lift passengers off their seats before they fell back down. The incident also occurred during meal service, when more people were likely moving around the cabin.
The digital flight data recorder showed vertical acceleration dropped from +1.35G to -1.5G in 0.6 seconds. Within the next four seconds, it swung back to +1.5G. Put together, these changes were enough to send an unbelted person airborne and then slam them down.
The pilot activated the seatbelt sign after the onset of turbulence at 7:49:23am UTC, but severe turbulence struck 17 seconds later – leaving little time for passengers to react. Flight crew had no time to make a cabin announcement.
Most injuries were to the head, neck and spine, including fractures, compressions, lacerations and dislocations. The passenger who died suffered heart failure and lung edema – a condition where there is too much fluid in the lungs.
Of the 229 people on board, 56 sustained serious injuries, 23 minor injuries and 149 were uninjured. Cabin damage included broken ceiling panels and punctured overhead bins.
TSIB said it cannot be over-emphasised that fastening seatbelts is the most effective way to prevent turbulence injuries. An airborne passenger who falls back down can also injure those around them.
“This occurrence serves as a reminder for all passengers, that turbulence may hit suddenly without warning, to always fasten their seat belts while seated and to refrain from moving about in the cabin unnecessarily, even when the fasten-seat-belt sign is off,” said investigators.
What happens next?
TSIB has recommended that Boeing develop guidance for flight crews and maintenance personnel to identify and respond to radar under-detection or non-detection.
The radar manufacturer was recommended to develop a means of recording weather display images to help diagnose faults.
A further recommendation to the International Civil Aviation Organization calls for larger aircraft built before 2023 to be retrofitted with systems that more reliably capture the data shown to pilots on their displays.
Recipients have 90 days to respond, stating whether they accept each recommendation and when they plan to implement it. Those that decline must explain why.
SIA has already taken several safety measures, including enhanced turbulence monitoring tools on crew tablets, updated guidance to flight crews on radar under-detection, and reporting protocols for such issues on its Boeing 777 fleet.
Flight crews have also received refresher training on turbulence management and in-flight procedures, with additional reminders for passengers to keep seatbelts fastened.
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