What causes air turbulence?

Turbulence is essentially unstable air that moves unpredictably. While it is often associated with storms, clear-air turbulence, which is invisible, is the most dangerous type.

The death of a British man and injuries impacting dozens of others on a Singapore Airlines flight that hit severe turbulence Tuesday is the latest incident to spotlight the potential dangers of flying through unstable air.

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

Such incidents are usually minor, and carriers have made steady improvements to reduce accident rates over time, but experts maintain that air travelers should stay vigilant — stressing the importance of wearing a seat belt whenever possible as a first line of protection.

THESE ARE THE FLIGHT ROUTES WITH THE MOST TURBULENCE

AP explains the essentials to understand about turbulence.

Turbulence is essentially unstable air that moves in a non-predictable fashion.

Most people associate it with heavy storms. But the most dangerous type is clear-air turbulence, which often occurs with no visible warning in the sky ahead.

Clear-air turbulence happens 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 difference in speed is big enough, the atmosphere can’t handle the strain, and it breaks into turbulent patterns like eddies in water.

Turbulence-related fatalities are especially rare — particularly on a commercial flight.

It can be tricky to predict, but experts stress that passengers' first line of defense is wearing a seat belt whenever possible.