SQ321 final report: What happened in the seconds before deadly turbulence hit
Investigators have reconstructed the moments before SQ321 encountered turbulence, revealing how a routine flight turned into a mid-air emergency within seconds.
by Abigail Ng · CNA · JoinRead a summary of this article on FAST.
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SINGAPORE: In less than a second, the gravitational force aboard Singapore Airlines (SIA) flight SQ321 changed so violently that passengers who were not belted up became airborne.
Within the next four seconds, another rapid G-force change sent them back down.
What happened in the minutes before and after those seconds is now documented in the final report by Singapore's Transport Safety Investigation Bureau (TSIB).
7:30am UTC (3.30pm Singapore time): The plane was cruising at 37,000ft approaching the west coast of southwest Myanmar. Cabin crew were preparing breakfast service and passengers were being woken.
No weather radar returns appeared on the flight crew's navigation displays, and they observed the immediate flight path was clear of cloud, with only high-level clouds visible in the distance.
7:44am UTC: The flight crew contacted Yangon air traffic control to request a slight change in route, citing weather – though the TSIB noted this was a tactical move rather than a genuine concern.
“Weather was cited by them to increase the likelihood of (air traffic control) approving their request for the direct route,” the report said.
Yangon’s air traffic control counter-offered an alternative route, which the crew accepted.
7:45am UTC: The flight crew adjusted the range of their navigational displays for flight path planning. One pilot said there were no weather returns and that the adjustment was routine. The cockpit voice recorder did not capture any discussions about weather between the pilots.
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7:49:23am UTC: SQ321 began experiencing turbulence, with vertical accelerations ranging from +0.44G to +1.57G over 17 seconds.
One pilot noticed airspeed climbing toward the overspeed range, alerted his colleague and deployed the speed brakes. The other pilot reduced cruising speed from Mach 0.84 to Mach 0.82 – the speed required for flying through turbulence to avoid exceeding structural design limits.
He also switched on the seat belt sign, calling out "seat belt on". There was no time to make a cabin announcement.
The aircraft's altitude meter registered a climb, and the autopilot pitched the nose down to hold 37,000ft, but the aircraft continued rising to 37,362ft.
7:49:40am UTC: Severe turbulence struck. Vertical acceleration dropped from +1.35G to -1.5G within 0.6 seconds, then surged back to +1.5G over the next four seconds.
A stall warning system is briefly activated. The crew disengaged autopilot and flew manually for 21 seconds to stabilise the aircraft, before switching autopilot back on at 7:50:05am UTC.
7:51am UTC: The area outside the aircraft appeared clear. The cockpit voice recorder captured the pilot-in-command saying: "How come suddenly … let me remove this and see" – but no further discussion followed on what he saw.
The TSIB said the pilot was surprised by the sudden onset of turbulence, and removed a sunshade to look out the window.
7:53am UTC: The pilot-in-command said: "We hit something, but I was on MAX … I was on MAX, I don't see anything here" – a reference to his weather radar gain setting.
Both pilots reported seeing no cloud outside, and neither navigation display showed weather returns.
After the aircraft stabilised and the turbulence subsided, the other pilot said: “Okay we are clear already … The weather is okay.” The pilot-in-command concurred: "Quite clear now."
Cabin crew then informed the cockpit of multiple injuries in the cabin.
7:55am UTC: The flight crew reported the severe turbulence to Yangon air traffic control and asked whether other aircraft had made similar reports. None had.
The senior first officer, who had been resting in the crew rest facility, made his way to the cockpit. Along the way he saw overturned service carts, broken serviceware and an injured cabin crew member being attended to.
8:01am UTC: The flight crew declared Mayday and requested a diversion to Bangkok.
8:06am UTC: Yangon air traffic control directed the aircraft to descend from 37,000ft to 31,000ft.
During the descent, the pilot-in-command saw altostratus – a type of greyish or bluish cloud sheet – and scattered cumulus clouds ahead. But navigation displays still showed no weather returns.
It was only when the aircraft descended below 31,000ft that weather returns appeared on the displays, they said.
8:45am UTC: SQ321 landed at Suvarnabhumi Airport in Bangkok. It arrived at its assigned parking bay about five minutes later, where medical personnel were waiting. The injured were treated and sent to hospitals.
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