The interior of Singapore Airlines flight SQ321 is pictured after an emergency landing at Bangkok’s Suvarnabhumi International Airport, Thailand on May 21, 2024.
| Photo Credit: Reuters

The story so far: On May 20-21, a Singapore Airlines flight, SQ321, with 211 passengers and 18 crew, from London’s Heathrow Airport to Singapore encountered severe turbulence while over the Andaman Sea/Bay of Bengal near the Irrawaddy Basin, Myanmar. A passenger passed away and several others suffered injuries of varying degrees. The crew decided to divert the Boeing 777-312ER to Bangkok, Thailand. The United States National Transportation Safety Board (NTSB) is to assist Singapore’s investigation — also because the aircraft is a Boeing jet.

What do we know about the incident?

Granular flight data shows the aircraft dropping rapidly before the crew began (“controlled”) descent from 37,000 feet to 31,000 feet. It also shows the aircraft had had an altitude deviation prior to this.

There has been much focus on ‘turbulence’. What have experts told The Hindu?

Turbulence occurs “by the relative movement of disturbed air through which an aircraft is flying”. It could be thermal or mechanical and can happen “either within or when it is clear of cloud”. Its severity depends on the “rate at which the speed or the direction of airflow/or both changes”.

According to Professor Guy Gratton, Associate Professor of Aviation and the Environment at Cranfield University, U.K., turbulence is basically what happens when there is friction between airflow or wind flowing in different directions. When it involves aviation, there are two main forms, which are Clear Air Turbulence (CAT), which happens around jet streams, and the other being inside or around cumulonimbus clouds. These clouds have very strong upwards air currents in the middle and downwards air current around the outside, he explains, which can result in quite serious turbulence. The faster an aircraft is, the more severe the response to the turbulence.

Prof. Richard Dale, Senior Lecturer in Aviation and Tourism at the University of West London, says turbulence consists of changes in the movement of air which the aircraft is moving through over a short distance. For example, there might be updrafts that are quickly followed by downdrafts, but also changes in the horizontal movement of the air. The movement of the air, to some degree, is random and unpredictable, although the location where turbulence will be encountered is more certain. These changes cause the lift produced by the aircraft wing to change for a short time, forcing the aircraft up or down, suddenly and unexpectedly. According to A.D. Ravishankar, former Director, Aviation Meteorology, India Meteorological Department, CAT is turbulence suffered by an aircraft above 18,000 feet.

Dr. Paul Williams, Professor of Atmospheric Science, University of Reading, U.K., says that turbulence fatalities on commercial flights are, fortunately, very rare. Turbulence on flights can be caused by storms, mountains, and strong air currents called jet streams. In this last case, it is called clear air turbulence, and can be difficult to avoid because it does not show up on the weather radar in the flight deck. He adds that a detailed analysis of the meteorological circumstances and the type of turbulence that affected the Singapore Airlines flight will take some time. He also says that there is strong evidence that turbulence is increasing because of climate change. “We recently discovered that severe clear air turbulence in the North Atlantic has increased by 55% since 1979. Our latest future projections indicate a doubling or trebling of severe turbulence in the jet streams in the coming decades, if the climate continues to change as we expect.”

Will passenger injuries lead to litigation?

As visuals from the Singapore incident show, there has been serious injury to some passengers. Injuries occur from passengers not wearing their seat belts resulting in them being violently thrown from their seats, the overhead bins opening causing items to fall, the cabin ceiling and panels coming off and hot beverages causing burn injuries. A Singapore Airlines spokesperson has told The Hindu that it has adopted a more cautious approach to managing turbulence in-flight.

Turbulence injuries have resulted in the realisation that winning a turbulence claim needs skill and knowledge of the factors that caused the incident. Aviation attorneys work with aviation and weather experts to plot the aircraft’s route, obtain satellite images of the weather at the time and location of the encounter, and to quickly secure airline data to help prove the claim. They even look at whether the crew knew there was bad weather ahead but decided not to deviate to save time, fuel, and airline money. In the U.S., for instance, aviation attorneys review government data and reports, Federal Aviation Administration and NTSB findings, and the airline’s procedures to obtain full and fair compensation. Magan vs Lufthansa German Airlines is one case where a passenger was injured and won a “substantial verdict pursuant to the Montreal Convention”.

What about technology in flight planning?

Bill Duncan, aviation forecast operations leader at The Weather Company (a weather forecasting and information technology company) has told The Hindu that there is a process behind a dispatcher or pilot planning a route, which includes meteorologists looking at flight planning guidance charts. There is also an accounting for year-round turbulence impacted by climate change. Extreme weather events have risen in severity since 2000. According to Mr. Duncan, there is no doubt that there is warming going on, which can impact and divide the jet stream. “As the jet stream buckles a bit because it is not as strong as it was in the past, you have all this energy associated with the jet stream up 30,000 feet or so, which is allowing colder air to spill south”. So the world is seeing major weather events happening more often.

Aviation meteorologists use model data, weather pattern recognition, and experience to help identify these areas of potential turbulence. Pilots get reports out ahead of their route on reported turbulence, and dispatchers are in contact with local meteorologists who actively watch routes and issue Flight Planning Guidance Charts (FPGs) and Significant Meteorological Information (SIGMETs). These SIGMETs are the information that the dispatcher can relay to the pilot about hazardous weather. With improvements in technology and science, there are better numerical weather prediction models. The Weather Company, for instance, has a Global high-Resolution Atmospheric Forecasting model which simulates the physics of the atmosphere to predict the weather and also uses artificial intelligence (AI) methods that build on weather forecasts to predict turbulence and other aviation hazards. Mr. Duncan adds that machine learning algorithms and AI are being used to find the links between historical weather and observations of turbulence. Separately, over 20 airlines now participate in the International Air Transport Association’s ‘Turbulence Aware Platform’.

The Singapore Airlines (SIA) Flight SQ321 that was rocked by severe turbulence on May 21 climbed and descended rapidly twice in 62 seconds, stunning the passengers with one dying of heart attack, as the aircraft flew over the Irrawaddy Delta region of Myanmar, it emerged on May 25.

One passenger — 73-year-old Briton Geoffrey Kitchen — died, and dozens were injured in the incident. It is the first SIA aviation accident involving a fatality since the SQ006 crash in Taiwan in October 2000.

Also read: What is aircraft turbulence and how common is it? | Explainer

As the flight, which was heading to Singapore from London, experienced sudden severe turbulence over the Irrawaddy Basin during the breakfast service, the pilot declared a medical emergency and diverted the plane carrying 211 passengers and 18 crew members to Bangkok’s Suvarnabhumi Airport, where the plane made an emergency landing at 3.45 pm (4.45 pm Singapore time).

Granular flight data from flight tracking website Flightradar24 shows that the Boeing 777-300ER climbed and descended rapidly twice in 62 seconds, starting from 3:49 pm Singapore time, as the plane was nearing the end of a non-stop flight from London to Singapore, The Straits Times newspaper reported.

During this time, the plane climbed from its cruise altitude of 37,000 feet to 37,400 feet and then dropped to 36,975 feet before settling back onto its cruise altitude.

This indicates that it was the rapid transition between the climb and descent caused by the turbulence — and not the actual change in altitude itself, which was relatively minor — that caused pandemonium in the cabin.

The Flightradar24 data — derived from a global network of ground-based receivers, satellites and radars that receive flight data from aircraft transponders — contradicts some earlier reports, which pinpointed the aircraft descending from 37,000 feet to 31,000 feet between 4.06 pm and 4.10 pm as the cause of the injuries.

This latter transition appears to be the pilots carrying out a controlled descent, most likely to assess the situation before diverting to Bangkok, according to the broadsheet report citing a commercial pilot who has flown both civil and military multi-engine passenger aircraft for more than 20 years.

Speaking on condition of anonymity, the pilot said the rapid climb would have introduced positive G-forces onto passengers, causing sitting passengers to feel like they have been pinned down in their seats.

The subsequent rapid descent would have resulted in negative G-forces, which would have sent unrestrained passengers and other loose items hurtling upwards onto the ceiling of the cabin, he added.

The embattled plane went through another cycle of rapid climb and descent, causing more damage and injuries, with some passengers and objects hitting the roof panels and overhead lockers before being flung back down.

This is reflected in the accounts of passengers on board SQ321 who reported being thrown onto the cabin roof, with Australian passenger Teandra Tukhunen recounting that she was abruptly woken up when she was thrown to the roof and then to the floor.

The G-force data would have been captured by the quick access recorder fitted onboard the aircraft. This is a flight data recorder designed to provide quick and easy access to raw flight data through means such as USB or mobile phone networks.

The Flightradar24 data showed that the Boeing 777 first attained a climb rate of 1,664 feet per minute (fpm) — or 507m per minute, double the height of 52-storey Capital Tower — before descending at 1,536fpm six seconds later. It rapidly returned to a climb rate of 900fpm a mere three seconds later, and then descended at 1,536 fpm after another 10 seconds.

Transport Minister Chee Hong Tat said on Friday that investigators from Singapore’s Transport Safety Investigation Bureau are going through data from the cockpit voice recorder and the flight data recorder.

The United States National Transportation Safety Board’s data from 2009 to 2018 showed that passengers injured in turbulence-related accidents were most often using, waiting for or walking to or from the toilet. The second-most common group was passengers who were seated but not belted up.

Thai hospital says 43 people still under treatment

Forty three people who were on board the Singapore Airlines flight remain hospitalised in Bangkok four days after the emergency, a hospital in the Thai capital said on Saturday.

The 43 patients are in three different hospitals in Bangkok, Samitivej Srinakarin hospital said in a statement.

At Samitivej Srinakarin hospital, where 34 of the patients are, seven are in intensive care — three Australians, two Malaysians, one British and one New Zealander, the statement said.

The other 27 patients from the flight at the hospital include eight British, six Australian, five Malaysian, and two Philippine citizens, the statement said.

Two people were discharged from Samitivej Srinakarin, while two from Samitivej Sukhumvit hospital were transferred to Samitivej Srinakarin to join hospitalised relatives, the statement said.

On Thursday, the Samitivej Srinakarin hospital director told reporters 22 patients had spinal cord injuries and six had brain and skull injuries, but none were life-threatening.