The risks of invisible turbulence – CAT

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In this new installment, We will talk about the risks of invisible turbulence or also called CAT, which can happen anywhere and at any time.

Always keep your seat belt fastened!

Although regular turbulence phenomena can be noticed and in a certain way managed appropriately, there is a phenomenon of turbulence that is almost impossible to foresee and can, as we have seen cases, cause problems in the aircraft with respect especially to the passengers, having cases where there have been injuries, This phenomenon is Turbulence in Clear Air. (CAT).

post writer by: Captain Rodolfo Estrella and Nicolas Larenas
FAA Commercial Pilot
Twitter: @rodo_estrella

Invisible turbulence or CAT clear air turbulence

Although turbulence is generally produced by the movement of air masses induced by various factors, This movement occurs either horizontally or vertically. (convectiva), usually severe turbulence can be avoided as they present visual cues of their presence, for instance, cumulonimbus or towering thunderclouds indicate strong updrafts, or lenticular clouds that, although they seem calm, have extremely dangerous turbulent qualities, among other.

These visual indicators, which are usually clouds, have a formation in the troposphere up to a certain level and are not usually present at high altitudes., so the detection of turbulence at higher levels is difficult.

At the limit of separation between the troposphere and the upper layer that is the stratosphere, There is a separation layer called the tropopause whose altitude varies depending on the latitudes, being higher at the equator and lower near the poles., near that limit there are air currents "jetstream", these planetary currents that have a flow from West to East and an origin thanks to solar heating on the atmosphere and a movement due to the coriolis effect produced by the rotation of the earth flow in an irregular path along the planet at certain latitudes.

These currents can have velocities of up to 160 km/h. Along these streams and especially on their edges, due to its own intensity, in addition to the interaction with lower air flows, there is turbulence, the severity of this turbulence will depend on the prevailing conditions at the time; Fortunately, this condition of extreme turbulence in these layers is usually, although intense, Of short duration, The phenomenon shearing It occurs over short distances, so severe turbulence conditions are not usually found in extended areas, but rather in "patches".

On some rare occasions these "jetstreams" present visual indicators of high-altitude cirrus clouds along the stream, however this is not always the case, which is why their effect is called "clear air turbulence" in English., which can have a very intense effect and cause injuries to passengers or crew who are not restrained in their seats as well as making loose objects a hazard as well.

Sadly, some scientists and meteorologists predict alterations in the movement and location of the "jetstream" thanks to global warming, the constant accumulation of heat at the poles is causing movements in these currents along different latitudes so it is not surprising to expect that the phenomenon will become more and more common.

While visually pilots are typically unable to obtain visual indications of CAT presence during flight, There are methods that help in flight planning to detect this kind of turbulence in a certain way., for example SIGMET meteorological reports where significant conditions are reported that can affect all flights, or even from reports of other aircraft that encounter the phenomenon and are reported to aircraft flying around the reporting area through air traffic control.

As we have indicated, airplanes and current technology, allows to detect many meteorological phenomena, including areas of turbulence, but the CATs, are impossible to detect by these equipments at present.

Incidents with invisible turbulence or CAT

There have been many cases of flights that have been affected by this phenomenon and even, the most recent in Argentina, left a dozen injured among passengers and crew, more significant damage to the interior of the aircraft.

Despite this extreme phenomena that can affect any plane and airline anywhere, aircraft and industry are highly prepared to withstand these and other extreme climatic effects.

Some of the most recent cases are:

• October 2018: Aerolineas Argentinas Airbus A330, flying over Bolivia with at least 15 wounded.
• July 2018: Austrian Airlines Airbus A320 in flight to Tel Aviv, 5 wounded.
• April 2018: Air India Boeing 787 in flight to delhi, 5 wounded.
• February 2018: Air Canada Boeing 767 in flight to San Jose, Costa Rica, 5 wounded.
• August 2017: American Airlines in flight from Athens to Philadelphia with 10 wounded.
• Mayo 2016: Etihad Airlines Boeing 777 from Abu Dhabi to Jakarta with 8 wounded .
• August 2016: Avianca in flight from Lima to Buenos Aires, more than ten wounded.

Among others…

Do not forget, always wear your seat belt. Crew instructions have a purpose and if it is always instructed to keep you buckled up, It is precisely because of these situations.

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