WHAT IS TURBULENCE?
WHAT CAUSES IT?
MOST air travellers are likely to have experienced turbulence at some point. As the plane jolts, belongings shake and fellow passengers can gasp with shock.
Turbulence occurs when planes fly into areas of disturbed air, which pushes aircraft around in a similar way to a boat in rough water. This is often caused by physical obstacles on the ground such as mountains or buildings as air flows over them hitting an aircraft like a wave.
Turbulence can also be caused by other passing aircraft which trigger the occurrence of different wind velocities, known as wake turbulence.
Some of the most violent turbulence is the result of thunderstorms which create huge vertical currents of disturbed air – often in patches up to 20 miles from where the weather system is occurring.
Aircraft can also encounter strong jet stream currents of air, which circulate around the globe at a similar height to many commercial planes.
These can disturb the surrounding air and in turn disrupt passing planes.
HOW PREDICTABLE IS IT FOR A PILOT?
EACH of the above factors can trigger what is known as CAT – clear air turbulence – which can appear unexpectedly because it does not show up on a flight’s weather radar. It is therefore difficult to navigate around – unlike storms which appear on the radar.
Marco Chan, who used to be a first officer with Hong Kong Airlines, said: “It is always invisible to the pilot or even to weather radar systems – it doesn’t pick up the turbulence on any of our screens or displays – so we just have to base [our understanding] on our own experience.
“And of course, if we see a thunderstorm in front of us, or we are in clouds, we know there’s going to be turbulence associated, so we try to avoid them. We don’t know we’re encountering turbulence until we encounter them.”