Investigation reveals timing of turbulence on fatal Singapore Airlines flight

IIt will likely take a long time for passengers and the aviation industry to recover from the shock of last week’s Singapore Airlines flight, which caused turbulence that resulted in one death and dozens of hospitalizations, but most of the damage occurred in less than five seconds, according to a preliminary investigation by Singapore’s Transport Safety Investigation Bureau.

A summary of the initial investigation results released on Wednesday said a drastic change in gravity that lasted just 4.6 seconds and resulted in a drop in altitude of 54 meters was “probably the cause of the injuries to the crew and passengers.”

Flight SQ321 from London to Singapore on May 20, which carried 211 passengers and 18 crew, was flying “normally” until it flew over southern Myanmar at an altitude of 37,000 feet and experienced “light vibrations”.

While the plane encountered this initial turbulence, likely caused by an updraft, for about 19 seconds, it climbed “uncontrollably” by about 362 feet, which the “autopilot” attempted to correct by pitching the plane downward. At the same time, the report said, the pilots noticed an “uncontrolled” increase in airspeed, to which they responded by deploying the airbrakes. The report added that at this point, “a pilot was heard calling out that the fasten seatbelt sign had been activated.”

About eight seconds later, the aircraft experienced a “rapid change” in gravity (G) as the recorded vertical acceleration decreased from +1.35G to -1.5G within 0.6 seconds. “This likely resulted in the occupants, who were not wearing seat belts, being lifted into the air,” the report said.

Over the next 4 seconds, gravity changed again from -1.5G to +1.5G, which the report says “likely caused the airborne occupants to fall back down.” At the end of the 4.6 second period of drastic gravity changes, the aircraft had fallen to an altitude of 37,184 feet.

The pilots attempted to stabilize the aircraft, which continued to experience increasing, albeit less severe, turbulence, by disabling the autopilot and operating it manually for 21 seconds before the aircraft returned to its normal altitude approximately one minute after the first turbulence occurred.

About 17 minutes later, after it was clear there were injuries that required medical attention, the pilots began descending the plane for an emergency landing at Thailand’s Suvarnabhumi airport. As of Wednesday, 42 passengers remained on board the flight in Bangkok, including 26 who are still receiving treatment in hospital, Singapore Airlines said in a statement.

The investigations are ongoing. Singapore Airlines, which previously announced it would revise its in-flight seatbelt policy, said in a separate statement that it “acknowledges” the Transportation Safety Bureau’s preliminary findings and is “fully cooperating with all relevant authorities.”