It’ll likely take a long time for the passengers and air travel industry to recover from the shock of the Singapore Airlines flight last week that experienced turbulence that led to one death and dozens hospitalized, but the bulk of the damage was done in less than five seconds, according to a preliminary investigation by Singapore’s Transport Safety Investigation Bureau.
A summary of the inquiry’s initial findings released on Wednesday revealed that a severe change in gravitational force, which took just 4.6 seconds and resulted in a 178-ft. altitude drop, “likely caused the injuries to the crew and passengers.”
The SQ321 flight traveling from London to Singapore on May 20, carrying 211 passengers and 18 crew members, was flying as “normal” until it passed over the south of Myanmar at an altitude of 37,000 ft. and began to experience “slight vibration.”
For about 19 seconds, while the aircraft was encountering this initial turbulence likely caused by an updraft, it rose “uncommanded” by about 362 ft., which “autopilot” attempted to correct by pitching the plane downwards. At the same time, the pilots, the report said, observed an “uncommanded” increase in airspeed, which they responded to by extending the speed brakes. The report added that, at this time, “it was heard that a pilot called out that the fasten seat belt sign had been switched on.”
About eight seconds later, the plane experienced a “rapid change” in gravitational force (G) as the recorded vertical acceleration decreased from +1.35G to -1.5G in the span of 0.6 seconds. “This likely resulted in the occupants who were not belted up to become airborne,” the report stated.
Over the next 4 seconds, the gravitational force changed again from -1.5G to +1.5G, which the report said “likely resulted in the occupants who were airborne to fall back down.” By the end of the 4.6-second period of drastic changes in G, the plane had dropped to an altitude of 37,184 ft.
The pilots tried to stabilize the aircraft, which continued to experience more turbulence albeit less severe, by “disengaging the autopilot” and “manually controlling” it for 21 seconds before the plane returned to its normal altitude about a minute after the initial turbulence was encountered.
Around 17 minutes later, after it was made clear that there were injuries necessitating medical attention, the pilots initiated the plane’s descent for an emergency landing at Thailand’s Suvarnabhumi Airport. As of Wednesday, 42 passengers who were on board the flight are still in Bangkok, including 26 who are still receiving treatment in hospital, Singapore Airlines said in a statement.
Investigations are ongoing. In a separate statement, Singapore Airlines, which announced earlier that it is revising its inflight seatbelt policy, said it “acknowledges” the transport safety bureau’s preliminary findings and is “fully cooperating” with all relevant authorities.
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