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Why causes air turbulence?

What is often referred to as 'air pockets' is in fact what  we call air turbulence. It is an irregular air motion that normally cannot be seen and often occurs unexpectedly. 

Flying through atmosphere with vigorous upward and downward moving air currents will expose one to a series of severe jolts or bumps similar to those felt in a fast speed boat over a choppy or rough sea.

Such bumps are determined by the stability of the atmosphere.  Stable air produce smooth flying condition.  On the other hand, if air is unstable, you are likely to experience some rough rides. Unstable air are often caused by the heating effect of the earth surface or air flowing over mountainous terrain. They are also found in micro bursts, thunderstorms, frontal systems and jet streams. So if you are flying within the vicinity of these phenomenon, you are very likely to encounter turbulence.

The effects of turbulence are akin to those of cobble-stones on a motor car - the faster the speed, the greater the jolts.  On a Boeing 777, the pilot will reduce the speed to the optimum turbulent speed and he would switch on the seat belt signs.

Bumpy flying conditions are also found at high altitude in clear air, hence known as clear air turbulence or CAT.  For reporting purposes by pilots or during forecast, CAT are classified by number codes from 0 to 6.  0 = no turbulence, 1 = light, 2 = light-to-moderate, 3 = moderate, 4 = moderate-to-severe, 5 = severe and 6 = extreme.  Please click here for a link to view the forecast of Clear Air Turbulence in the USA.

The severity of CAT varies within a wide limit but in extreme turbulence, airplane can suffer some minor damage.  With severe turbulence there is a tendency for those who are not strapped with their seat belts to be lifted from their seats.  Slight CAT can sometime occur up to 20% of occasions during flights up to 4 hours.

In most cases of severe CAT, they are likely to occur near jet streams.  The causes of CAT cannot always be established but usually it occur where there is considerable changes of winds in a short distance either horizontally or vertically.

In June 1995, the FAA issued a public advisory to airlines urging the use of seat belts at all times when passengers are seated as a precaution against unexpected turbulence.

Among non-fatal accidents, in-flight turbulence is the leading cause of injuries to airline passengers and flight attendants. Each year, according to the FAA, about 58 air passengers in the United States are injured by turbulence while not wearing their seat belts.

On December 5, 1996, 16 people suffered injuries, including a 7 month old baby, when an American Airlines jetliner ran into clear air turbulence over Colorado.

From 1981 to November 1996, there were 252 reports of turbulence affecting major air carriers. Two passengers died, 63 suffered serious injuries and 863 received minor injuries. Both fatalities involved passengers who were not wearing their seat belts. Two third of turbulence-related accidents occurs at or above 30,000 feet.

Generally, flying through prolonged light-to-moderate turbulence, can be fairly uncomfortable to the passengers and the crew. The pilots are very conscious of this fact and will make all effort to lessen the discomfort by requesting a change of flight levels or deviating off track.

 Information of Interest to Passengers

  • It is advisable to have your seat belt on at all times even though the Captain has switched off the signs for the commencement of in-flight services if you do not intend to leave your seat to go to the toilet.
  • When fasten seat belts announcement are made, ensure the seat belts are tightly secured.
  • Ensure the baggage doors located above your head are secured before the aircraft takes off. Severe turbulence can dislodge an unsecured door and the heavy baggage may drop down and injure yourself !

Question via email


 First I would like to say thank for your website.  It is very informative.  I am a frequent flyer as I am a business traveler and am on a plane every week.  I normally fly on the Boeing 737 Series jets up and down the West Coast of the US.  

My question is more general concerning turbulence, more specifically turbulence during initial decent and approach to the runway.  How do pilots deal with this?  I normally am not fearful however in these circumstances I feel my anxiety increasing. 

Kevin Quille
Portland, Oregon
Hi Kevin,
Thank you for your interest on Air Turbulence.  I know of many  air travelers who told me of their great anxieties about air turbulence during flight, especially where they have no control over it.
Generally, pilots would inform passengers about the weather they would encounter during the descent and approach to the Runway.  This would allow the passengers to anticipate the turbulence and calm any fears that they may have. Normally the 'Seat Belt Sign' would be switched on.
During descent on a cloudy day, one would expect some turbulencePilot makes use of the weather radar to avoid the most active areas of turbulence unless it is unavoidable due to other traffic (then you are in for a rough and uncomfortable ride !). As long as you are securely fastened, turbulence is nothing to worry about except for some discomfort (imagine yourself in a bus traveling on a road with lots of potholes!)
Approach to the Runway - when landing on the Runway with strong crosswinds over uneven terrain in the vicinity of the approach area or where wind shear (see my FAQs on this topic) is likely, turbulence also cause great anxiety to many passengers.  Again, this may be uncomfortable but there are limits whereby the turbulence becomes a safety hazard. In this situation, pilots have been trained to abort the landings, divert to another suitable airport, or land on another Runway where there are no reported turbulence by other pilots.
In more advanced aircraft, like the Boeing 777, there are aural warnings emitted from the aircraft computers about any impending wind shears, which are inevitably accompanied by severe turbulence.  Pilots would react to these warnings by aborting the landing.
In certain advanced airports, there are also ground equipment to warn pilots about low level wind shears (and turbulence) through the Air Traffic information service.  Again, pilots would be cautious either to abort the landing or wait for the turbulence to subside before attempting a safe landing.
I hope I have been able to adequately explain to you about turbulence during initial descent and approach to land, and to defuse any fears or anxiety that you may have on your next flight.
Always have your seat belts tightly fastened during descent and landing and you would feel more secured any time.
Fly Safely !
Capt Kay

Hi Capt Kay,
Thanks for spending time answering my question.  You do a great service to air travelers who may not understand the "mechanics of flight."  I will be sure to check back to your site for information on flying the Triple 7.



So from your experience, how often do severe air turbulence occur? And on an average, how long will the turbulence last? Would you give me some more details ??



Hi Tom,

Thanks for your queries.  From my experience, I do encounter air turbulences almost daily during the course of my normal flying but they are classified as light to medium in nature and nothing to worry about.  Severe air turbulence can arise when one is trapped inadvertently inside a severe thunderstorm. This may be because the pilot was trying to navigate through some line squalls and the weather radar was not very effective or the aircraft may be flying in the vicinity of micro-burst activities. (See my article on Wind shear)

Severe air turbulence can also be quite prevalent in Jet Streams found near the Frontal systems.  In fact, they are more likely to be associated with clear air turbulence, something you cannot see but know that they are present because of their proximity to the Jet Streams.  Such severe air turbulences are predictable and are often shown in the pilot's weather chart. To avoid severe air turbulence, pilots often request for a higher or lower level or to a  re-routing.

Sometimes such requests may not be possible due to other air traffic and you have to bear with it for a while.  Always remember to have your seat belts securely fastened.  

The pilots will take the necessary precautions like reducing the airspeed to comply with the structural limitation and warning everyone to be securely fastened onto their seats.  

It is difficult to say how long an average severe turbulence will last because it will depend on your journey. It can be as short as 15 minutes to as long an hour or so.  If the track to your destination is smack inside the area of clear air turbulence, then you may be in for a long and rough ride. Otherwise the pilots will endeavor to avoid it because it can be quite uncomfortable to everyone inside the aircraft.


Capt Kay

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