Turbulence

Turbulence is the irregular movement of air, caused by eddies, vertical currents and changes in wind speed or direction.

It may range from:

• light bumps;
• to severe changes in airspeed and flight path;
• loss of control;
• stall; or
• structural overload.

Turbulence may be associated with:

• wind shear;
• thunderstorms;
• convection;
• fronts;
• hills and mountains; and
• wake from other aircraft.

Wind Shear

Wind shear is a rapid change in wind speed and/or direction over a short distance.

It may be:

Vertical Wind Shear

A change in wind speed or direction with a change in height.

Horizontal Wind Shear

A change in wind speed or direction across a horizontal distance.

Wind shear may occur near:

• temperature inversions;
• fronts;
• thunderstorms;
• convective cloud;
• mountain waves; and
• microbursts.

The region where the wind changes is called the shear zone and may contain considerable turbulence.

Effect of Low-Level Wind Shear

Wind shear is particularly hazardous during:

• take-off;
• approach; and
• landing,

because the aircraft is close to the ground and there is little height available for recovery.

A sudden reduction in headwind can cause: