TURBULENCE
Turbulence is air movement that normally cannot be seen. It may occur when the sky appears to be clear and can happen unexpectedly. It can be created by any number of different conditions, including atmospheric pressures, jet streams, mountain waves, cold or warm fronts, or thunderstorms.
Turbulence is the leading cause of inflight injuries. There are countless reports of occupants who were seriously injured while moving about the passenger cabin when clear air turbulence is encountered.
The causes Thermals - Heat from the sun makes warm air masses rise and cold ones sink Jet streams - Fast, high-altitude air currents shift, disturbing the air nearby Mountains - Air passes over mountains and causes turbulence as it flows above the air on the other side Wake turbulence - Near the ground a passing plane or helicopter sets up small, chaotic air currents Microbursts - A storm or a passing aircraft stirs up a strong downdraft close to the ground.
Different intensities of turbulence Light Chop. Slight, rapid, and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude.
Light Turbulence. Slight, erratic changes in altitude and/or attitude. Occupants may feel a slight strain against seatbelts. Unsecured objects may be displaced slightly. Food service may be conducted and little to no difficulty is encountered in walking.
Moderate Chop. Rapid bumps or jolts without appreciable changes in aircraft altitude or attitude.
Moderate Turbulence. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Occupants feel definite strain against seatbelts. Unsecured objects are dislodged. Food service and walking are difficult.
Severe. Large, abrupt changes in altitude and/or attitude. Usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Occupants are forced violently against seatbelts. Unsecured objects are tossed about. Food service and walking are impossible.
Extreme. Aircraft is violently tossed about and is practically impossible to control. May cause structural damage.
The reactions inside aircraft vary from occupants feeling a slight strain against their seat belts and unsecured items being jostled, through to occupants being forced violently against seat-belts, and unsecured items being tossed about. (Imagine what it would be like if you were not wearing a seat belt!)
Clear air turbulence There are several notable problems with clear air turbulence: • It cannot always be foreseen so there is no warning • It is usually felt at its mildest in the flight deck and is generally more severe in the aft section • It can occur when no clouds are visible • Aircraft radars can’t detect it • It is common at high altitudes, where cruising airline suddenly enter turbulent areas
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