Clear Air Turbulence (CAT)

Definition

Clear Air Turbulence (CAT)  is described as sudden severe turbulence taking place in cloudless areas that causes violent buffeting of aircraft.

This term is generally implemented to higher altitude turbulence associated with wind shear.

The most comprehensive definition is high-altitude turbulence encountered outside of convective clouds.

This includes turbulence in cirrus clouds, inside and inside the place of standing lenticular clouds and, in a few cases, in clear air inside the vicinity of thunderstorms. Generally, though, CAT definitions exclude turbulence resulting from thunderstorms, low-altitude temperature inversions, thermals, sturdy surface winds, or nearby terrain features.

Description

There are two types of CAT:

  • Disruption to the smooth horizontal flow of air.
  • Turbulence caused by vertical currents of air in an unstable atmosphere.

 

Common causes and sources of CAT are:

  • Jet Stream. A Jet Stream is a narrow, fast moving modern-day of air, normallynear the Tropopause and generated because of the temperature gradient between air masses.
  • Although not all jet streams have CAT related to them, there can be good sized vertical and horizontal Low Level Wind Shearon the rims of the jet movement giving upward thrust to on occasion excessive clean air turbulence.
  • Any CAT is most powerful on the cold side of the jet stream in which the wind shear is greatest. In the location of a jet stream,
  • CAT can be encountered anywhere from 7,000 feet below to about 3,000 feet above the tropopause.
  • Because the strong vertical and horizontal wind shear happens over brief distances, this jet stream related CAT tends to be shallow and patchy so a descent or climb of as low as 2,000 feet is often enough to exit the turbulence.
  • High ground disturbs the horizontal go with the flow of air over it, inflicting turbulence. The severity of the turbulence relies upon on the energy of the air drift, the roughness of the terrain, the charge of change and curvature of contours, and the elevation of the high floor above surrounding terrain.
  • Thunderstorm Complexes.Cumulonimbus (Cb) cells have sturdy vertical currents. Aircraft passing inside 20 nautical miles horizontally, or less than 5,000 toes above the top, of a Cb may come upon CAT.

Effects

  • Structural Damage.Aircraft can go through structural harm as a result of encountering extreme clear air turbulence. In extreme cases this will cause the break-up of the aircraft. In even moderate turbulence, damage can occur to fittings inside the aircraft, especially because of collision with unrestrained objects of shipment or passenger luggage. Prolonged publicity to turbulence will shorten the fatigue existence of the aircraft.
  • Physical Injury to Crew/Passengers.If stuck unaware, passengers and crew shifting around in the plane cabin can be injured. In one case, wherein a B747 encountered CAT over the Pacific Ocean, numerous passengers and crew were critically injured and one passenger eventually died.
  • Impaired Flight Crew Performance.Moderate or Severe turbulence can make simple tasks, including reading instruments, near impossible.

Defenses

  • SIGMET Charts deliver forecasts of the place and level of clean air turbulence. Information on neighborhood terrain brought on CAT may be contained in appropriate Aeronautical Information Publications (AIPs).
  • Restraint Systems. Passengers and crew should fit seat belts and harnesses when seated to protect them in the event of unforeseen turbulence.

 

Solutions

  • Slow down.Reducing the aircraft speed reduces the risk of structural damage and reduces vibration making instruments easier to read.
  • Strap in.Notify the crew/illuminate seat belt sign. All passengers and crew should immediately sit down and fit seat belts/harnesses.
  • Switch on Engine Ignition– Certain aircraft types recommend turning ignition on to prevent the turbulent airflow from flaming out engines.
  • Inform ATC.Notify ATC/warn other aircraft on chat or guard/emergency frequency (121.5 or 243.0). Request clearance to climb/descend or diverge from track to escape turbulence.
  • Assess Damage/Injuries.Carry out a damage assessment and ascertain condition of any injured passengers. Consider precautionary diversion.

Suspend Cabin Service. Obviously the serving of hot drinks and meals during turbulent conditions puts both cabin

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