Singapore Airlines horror: What is in-flight turbulence and can pilots avoid it?

A Singapore Airlines flight hit severe turbulence over the Indian Ocean and descended 6,000 feet (around 1,800 metres) in about five minutes, the carrier said on Tuesday, 21 May.

A British man died and dozens of passengers were injured, some severely, the authorities said.

The latest incident has highlighted the potential dangers of flying through unstable air.

So, what exactly is turbulence? How common is it? Can pilots prevent it?

Let’s take a closer look.

What happened?

The Boeing 777 flight from London’s Heathrow airport to Singapore was diverted and landed in stormy weather in Bangkok. There were 211 passengers and 18 crew members aboard.

According to tracking data captured by FlightRadar24, Singapore Airlines Flight SQ321 cruised at an altitude of 37,000 feet (11,300 metres).

At one point, the Boeing 777-300ER suddenly and sharply descended to 31,000 feet (9,400 metres) over three minutes and stayed there for less than 10 minutes before diverting and landing in Bangkok less than a half-hour later, according to the data.

The sharp descent occurred as the flight was over the Andaman Sea, near Myanmar.

The aircraft sent a “squawk code” of 7700 at that time, an international emergency signal.

Kittipong Kittikachorn, general manager of Suvarnabhumi Airport, said at a news conference that the sudden descent occurred as passengers were being served food.

He said seven passengers were severely injured and 23 passengers and nine crew members had moderate injuries, and 16 with less serious injuries received hospital treatment and 14 were treated at the airport.

The airport official said the 73-year-old man may have had a heart attack, though that hadn’t been confirmed.

His name wasn’t immediately released.

According to India Today, he was accompanied by his wife, who has also been hospitalised.

Based on witness accounts, the number of injuries and the airliner’s sharp descent, experts point to the significant safety hazards that in-flight turbulence poses to airline passengers and crews.

What is turbulence?

Turbulence is essentially unstable air that moves in a non-predictable fashion. It is often linked to heavy storms.

The most dangerous is clear-air turbulence, which has no visible warning in the sky ahead. It occurs most often in or near the high-altitude rivers of air called jet streams.

The culprit is wind shear, which is when two huge air masses close to each other move at different speeds.

If the speed difference is big enough, the atmosphere can’t handle the strain, and it breaks into turbulent patterns like eddies in water, according to The Associated Press.

“When you get strong wind shear near the jet stream, it can cause the air to overflow. And that creates these chaotic motions in the air,” Thomas Guinn, chair of applied aviation sciences department at Embry-Riddle Aeronautical University in Daytona Beach, Florida, explained to the news agency.

While turbulence-related fatalities are quite rare, injuries have piled up over the years.

According to meteorologists and aviation analysts, reports of turbulence encounters also have been increasing. They point to the potential impacts that climate change may have on flying conditions.

Though planes hitting bumpy air are minor, airlines have made steady improvement to reduce accident.

How common are turbulence-related injuries?

Tracking total number of turbulence-related injuries is tough, however, some individual countries have published national data.

According to National Transportation Safety Board, the United States witnessed more than one-third turbulent incidents of all airline incidents from 2009 through 2018. Most of them resulted in one or more serious injuries but no damage to the plane.

Between 2009 and 2022, 163 people were seriously injured and needed hospital treatment for at least two days, according to the figures. Most of them were flight attendants, who are particularly at risk since they are more likely to be out of their seats during a flight.

“It’s not uncommon to have turbulence encounters that cause minor injuries up to, say, a broken bone. But fatalities are very, very rare — especially for large transport aircraft,” AP quoted Larry Cornman, a project scientist at the National Science Foundation’s National Centre for Atmospheric Research who has long studied turbulence.”

According to Stuart Fox, director of flight and technical operations at the International Air Transport Association (IATA), the last clear air turbulence-related death reported from a major carrier took place in 1997.

Since then, a few fatalities on smaller planes have been reported. This includes a death on a private jet last year, Fox said.

Over the year, the standardised safety procedures, which include reviewing weather forecasts, having pilots report when they encounter turbulence, suspending cabin service during rough air, have significantly prevented more cases of serious injuries

Can pilots avoid it?

There are various methods that pilots can employ to avoid turbulence, like using a weather radar display. Sometimes they can simply see and fly around thunderstorms.

However, according to Doug Moss, a former airline pilot and safety consultant, clear-air turbulence “is altogether another animal.”

It can be devastating, he said, “because the time before the incident can be very calm, and people are caught off-guard.”

Air traffic controllers will warn pilots after another plane runs into clear-air turbulence, Moss said.

Many pilots also look at the upper-level jet streams along their route for signs of wind shear, then plan to fly above, below or around those areas, he said.

Modern planes are strong enough to handle just about any turbulence.

Cabin areas such as overhead bins may receive cosmetic damage, “but these don’t impact the structural integrity of the planes,” Moss said.

Is climate change to blame?

There are a number of possible explanations for rising turbulent events, but several researchers have pointed to potential climate impacts.

Guinn, of Embry-Riddle Aeronautical University, explains that some predict climate change could alter the jet stream and up the wind shear, which would consequently drive up turbulence in the air.

In a statement on 21 May, Paul Williams, a professor of atmospheric science at the University of Reading in England, said there was “strong evidence that turbulence is increasing because of climate change.”

He cited his research team’s latest finding as an example which discovered that severe clear-air turbulence in the North Atlantic has increased by 55 per cent since 1979.

The team’s latest projections signal that severe turbulence in the jet streams could double or triple in the coming decades if global conditions continue as expected, he said.

Still, several experts believe other factors could also be at play.

Cornman notes that there could be a rise in overall air traffic — which may increase turbulence encounters as the number of flight tracks, including those in areas of more turbulence, goes up.

How passengers can stay safe?

Buckle up.

That’s what all passengers can simply do.

Predicting turbulence can be tricky, thus experts stress that keeping the seat belt fastened is the best defence in the air.

“Planes are generally built to withstand turbulence,” Guinn said, noting that passengers not wearing their seat belts is a large source of injuries from in-flight turbulence.

While there’s no solid precaution, wearing a seat belt highly increases an individual’s chance of avoiding serious injuries.

With inputs from The Associated Press