Explained: What Probe Into Turbulence-Hit Singapore Airlines Flight Reveals

Last week, Singapore Airlines Flight SQ321, en route from London to Singapore, was dramatically disrupted by severe turbulence while cruising at 37,000 feet over Myanmar. Preliminary findings released by Singapore's Transport Safety Investigation Bureau (TSIB) provide a detailed account of the incident, revealing the violent nature of the turbulence and its consequences.

On May 21, Flight SQ321, a Boeing 777-300ER carrying 211 passengers and 18 crew members, encountered unexpected and extreme turbulence. This sudden turbulence resulted in one death, with a passenger suspected of suffering a heart attack, and numerous injuries among those on board. The flight was forced to make an emergency landing in Thailand's capital Bangkok.

"The aircraft experienced a rapid change in G (gravitational force). This likely resulted in the occupants who were not belted up to become airborne," the Singapore transport ministry said in a statement, citing a report by the Transport Safety Investigation Bureau of Singapore.

According to TSIB findings, Flight SQ321 departed from London on May 20 and maintained a normal flight path until the turbulence incident.

The investigation revealed that the gravitational force (G-force) fluctuated between +0.44G and +1.57G over 19 seconds, causing initial vibrations. The aircraft experienced an uncommanded altitude increase to 37,362 feet, likely due to an updraft. The autopilot attempted to correct this by pitching the aircraft down, and the pilots managed an uncommanded airspeed increase by extending the speed brakes.

"The vertical acceleration changed from negative 1.5G to positive 1.5G within 4 seconds. This likely resulted in the occupants who were airborne to fall back down. The rapid changes in G over the 4.6 seconds duration resulted in an altitude drop of 178 ft (54 m), from 37,362 ft to 37,184 ft. This sequence of events likely caused the injuries to the crew and passengers," the report said.

How The Crew Responded

During the turbulence, the pilots disengaged the autopilot and manually controlled the aircraft for 21 seconds to stabilise it.

They re-engaged the autopilot at 07:50:05 UTC and the aircraft returned to its cruising altitude of 37,000 feet by 07:50:23 UTC.

After assessing the injuries and the severity of the situation, the pilots diverted the plane to Suvarnabhumi Airport in Bangkok.

They coordinated with air traffic control to ensure medical services were ready upon landing.

The aircraft began a controlled descent at 08:06 UTC and landed safely at 08:45 UTC without encountering further severe turbulence.

The violent turbulence resulted in several injuries among passengers and crew members. The sudden shifts in G-force and altitude threw unsecured individuals against the cabin structure, causing severe trauma. Tragically, one passenger suffered a suspected heart attack and could not be revived.

The TSIB, in collaboration with the National Transportation Safety Board (NTSB), the Federal Aviation Administration (FAA), and Boeing, continues to investigate the incident. Data from the flight data recorder (FDR) and cockpit voice recorder (CVR) have been analysed to compile a detailed chronology of the event.

"We are committed to supporting our passengers and crew members who were on board SQ321 on that day, as well as their families and loved ones," Singapore Airlines said in a statement on Wednesday.