SINGAPORE - A Singapore Airlines flight had to make an emergency landing in Bangkok on May 21 after encountering sudden, extreme turbulence, which resulted in one death and dozens of passengers injured.

The circumstances surrounding the incident on SQ321 is under investigation, though one expert said it was one of the worst he has seen in his 30 years in the industry.

While it is not uncommon to encounter in-flight turbulence, such episodes can have severe consequences.

Between 2009 and 2022, the Federal Aviation Administration in the United States recorded that 163 passengers and crew members were seriously injured by turbulence on aircraft registered in the United States.

Here is what you need to know about turbulence.

1) What is turbulence?

Dr Matthias Roth described atmospheric turbulence as irregular and chaotic and unpredictable motions in the airflow.

Turbulence can be caused by storms, mountains, weather fronts and strong air currents such as jet streams, said the professor of urban climatology at the National University of Singapore’s department of Geography.

Turbulent motions are usually not visible, he noted. This particular type of turbulence, which is often called clear air turbulence, is caused by changes in wind speed, air temperature or pressure over short distances. They are difficult to avoid because they are not directly visible, are hard to predict and do not show up on a weather radar.

Associate professor Steve Yim from the Asian School of the Environment at the Nanyang Technological University (NTU) said turbulence can be caused by wind shear – a sudden change in wind speed and direction due to differences in air temperatures at different altitudes.

The World Meteorological Organisation called wind shear is a “major hazard” for aviation, especially when operating at lower altitudes.

2) How common are injuries related to turbulence?

America’s National Transportation Safety Board (NTSB) reported that more than a third of all airline incidents in the United States from 2009 through 2018 were related to turbulence, most of which resulted in one or more serious injuries but no damage to the plane.

Fatalities from encountering turbulence in flight are rare – none were captured by the Federal Aviation Administration (FAA) between 2009 and 2022.

But there were 129 crew m...