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    Is Turbulence Dangerous?

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    • Is Turbulence Dangerous?

      A look at if turbulence is dangerous to passenger jets? Can turbulence make a plane crash?

    Is Turbulence Dangerous?

    What is turbulence and is it dangerous for passenger aircraft?

    Is Turbulence Dangerous for Passenger Jets?

    Whilst for some people, experiencing turbulence can be upsetting, turbulence does not pose a danger to the structural integrity of the aircraft. Even in severe turbulence, the plane will keep flying and the overall safety of the aircraft is only compromised in extreme circumstances, which most pilots will never experience. However, turbulence can be dangerous for the passengers if they are not seated with their seatbelt fastened as in very severe cases, turbulence can cause occupants to be thrown around the aircraft cabin resulting in injury. Every year there are reports of passengers experiencing broken bones due to the effects of turbulence, and this is always because they aren’t wearing their seat belt.

    Turbulence is probably the single most common cause of anxiety for airline passengers, yet it rarely causes the pilots any concerns about the safety of the aircraft. Turbulence is very common and is usually experienced to some degree every single flight. In all but the most extreme cases, turbulence is not a danger to the safety of the flight, rather, it’s more of an uncomfortable inconvenience. In essence, turbulence is annoying but rarely dangerous and your plane won’t crash because of it.

    Nervous passengers also have a tendency to think that the turbulence is worse than it actually is. For example, whilst many passengers might refer to experiencing ‘Severe’ turbulence, as far as the official categorisation goes and the pilots are concerned, it’s very likely to just be ‘light’ or ‘moderate’. Genuine severe turbulence is very rare. I’ve experienced it twice in around 6000 flying hours over 15 years, with many of those hours spent crossing the Atlantic, where the jet stream can make it a particularly bumpy area.

    The best way to see how bad the turbulence is expected to be is to watch the Cabin Crew. If they have stopped the service and taken their seats, you know it’s about to get pretty bumpy!

    What is Turbulence?

    Turbulence is a bit like driving down a road with lots of pot holes in a car, except in this case, it’s the air in the sky that’s a bit bumpy and rough. There are a number of different types of turbulence, some of which can be detected by most commercial aircraft, whilst other types are invisible and very difficult to predict.

    Different Types of Turbulence

    Convective Turbulence

    Convection (rising air) is the process which causes clouds to form. This process can also be responsible for creating turbulence which is associated with clouds, particularly cumulus cloud types. The greater the vertical extent of the cloud (i.e. the taller it is), the greater the up drafts and therefore the worse the turbulence is likely to be. It is particularly bad when flying through Cumulonimbus clouds (which are associated with very heavy rain showers / hail or thunderstorms).

    Clear Air Turbulence

    Clear Air Turbulence (nicknamed CAT) is caused by jet streams which are very strong corridors of wind found at high altitudes. They can reach in excess of 150mph and whilst this can dramatically reduce the flight time if the wind is behind you, they can also be responsible for strong levels of turbulence.

    Jet Streams form between the boundaries of warm and cold air and therefore vary in position throughout the year. Whilst the position of the jet stream isn’t difficult to predict, the turbulence associated with it is very difficult to accurately pinpoint.

    Low Level Thermals

    This is hot air rising from the ground which is prevalent on hot days at low altitudes, particularly when over land. They are worst when the ground is at its hottest, so typically in the afternoon.

    Wake Turbulence

    Unlike the other types of turbulence mentioned so far which are weather related, wake turbulence is phenomenon caused by other aircraft.

    When flying, every aircraft produces wake turbulence and is an aerodynamic byproduct produced by teh wing as lift is generated (which is what makes the aircraft fly). For those who are technically minded, wake turbulence is produced through the interaction between low pressure air at the top of the wing and high pressure air at the bottom. The air moves from the bottom to the top of the wing at the wing tip which causes wing tip vortices. These vortices are left like a trail behind the aircraft, a bit like the wake of a boat – it can hang around for a while afterwards, and the calmer the wind, the longer it stays.

    If you fly through another aircraft’s wake vortex, you might experience turbulence from it. The bigger the aircraft, the bigger the aircraft’s wake. So the wake of an A380 is much bigger than that of a B737. Equally, the bigger/heavier the aircraft, the less it will be effected by wake turbulence. For example, an A380 flying through the wake of a B737 wouldn’t feel a great deal, but if it was the other way round, it could be very bumpy for a few seconds.

    Wake turbulence is often very violent and it usually only lasts for a few seconds. In extremely rare circumstances, this type of turbulence has caused aircraft to crash.

    To make sure wake turbulence doesn’t pose a danger to commercial aircraft, air traffic control apply minimum time or distance spacing between aircraft to ensure adequate separation. Each aircraft type has to take-off or land at specific time or distance behind the other type of aircraft – it can’t get too close. The bigger the aircraft in front and the smaller the aircraft behind, the bigger the gap has to be,

    Wind

    At low altitudes (close to the ground) wind is subject to the friction and interference of the Earth’s surface and anything on it (like buildings etc). As a result, low level wind is often less laminar/smooth (straight and steady) and more turbulent (varying in direction and speed) than at higher altitudes. Rapid variations in direction and speed can cause turbulence at low level, particularly when the aircraft is on final approach coming into land.

    Can Pilots Detect Turbulence?

    Pilots can detect certain types of turbulence using an onboard weather radar. The radar highlights where there are large quantities of water droplets (rain) on the pilot’s instruments. Generally speaking the bigger the rain drops, the bigger the cloud, and the more turbulent it will be inside that cloud. The pilots make a judgement on if they can fly through the cloud or avoid it by flying around it.

    Can Pilots Avoid Turbulence?

    Sometimes. There are some types of turbulence which can’t be detected, like Clear Air Turbulence or CAT which is associated with a Jet Steam. Sometimes it’s forecast and the pilots can do their best to avoid it by avoiding certain flight levels, but sometimes the forecasts are wrong and the pilots fly into it without knowing it’s there. That’s why they ALWAYS recommend that passengers keep their seat belts fastened whenever seated, regardless of the status of the fasten belt sign.

    Prior and during flight, the pilots will be studying various weather charts which predict where any areas of Clear Air Turbulence is located, or where any thunderstorm (cumulonimbus) clouds mights occur during the flight. It provides the flight crew with a rough location and the altitudes that turbulence may be encountered. The pilots can then take action at the pre-flight planning stage to adjust the planned flight level or routing of the flight if required.

    The pilots will often put the fasten seatbelt signs on prior to experiencing any turbulence based on the forecast or following communication with ATC or other aircraft.

    Pilot Actions in Turbulence

    Passenger comfort is a high priority for pilots so when the aircraft enters turbulence they are almost always doing their best to get out of it. This is not because it’s dangerous, but because it’s uncomfortable for both the passengers and crew. The pilots don’t like it any more than you do. To get out of it, pilots are regularly speaking to air traffic control and other aircraft to see what levels are free of turbulence or where along the route the turbulence might subside.

    Unfortunately on some days, turbulence is prevalent at all levels and is impossible to avoid. In extremely rare cases where there is severe to extreme turbulence, the pilots may decide to divert the aircraft and land, but this is very, very rare.

    When at the cruise altitude, if the aircraft finds itself in moderate or severe turbulence, or the pilots are aware that there is turbulent air ahead, they will proactively adjust the speed of the aircraft in order to fly at the aircraft’s ‘turbulence penetration speed’. This is a speed, determined by the manufacturer of the aircraft type, to provide a suitable buffer between the aircraft’s maximum and minimum speed as turbulence will usually cause the airspeed to fluctuate.

    So in order to avoid or minimise the effect of turbulence on the aircraft pilots may take the following actions:

    • Change the altitude of the aircraft (climb or descend into smoother air)
    • Speed up or slow down to the aircraft’s turbulence penetration speed
    • Change the lateral routing (turn right or left) to avoid certain area of known turbulence
    • Turn the seat belts signs on
    • Make a PA to reassure passengers
    • Tell cabin crew to stop the service and/or take their seats

    Turbulence Categorisation

    Turbulence is categorised into Light, Moderate and Severe. The official definitions from IATA are as follows:

    Light Turbulence Definition:

    Light turbulence might cause slight, erratic changes in aircraft altitude and/or attitude (pitch, roll, yaw).

    • Liquids are shaking but not splashing out of cups
    • Carts can be manoeuvred with little difficulty
    • Passengers may feel a light strain against seat belts

    Moderate Turbulence Definition: 

    Moderate turbulence can be defined as slight changes in aircraft altitude and/or attitude and a greater intensity of motion than light turbulence. However, the aircraft remains in control at all times.

    • Liquids are splashing out of cups
    • Difficulties to walk or stand without balancing or holding on to something. Carts are difficult to manoeuvre
    • Passengers feel definite strain against seat belt

    Severe Turbulence Definition:

    Severe turbulence is defined as the aircraft being subject to large, abrupt changes in altitude and/or attitude. It usually causes large variations in airspeed and the aircraft may at times be out of control.

    • Items in the cabin are falling over unsecured objects are tossed about.
    • Walking around the aircraft is impossible
    • Passengers are forced violently against seat belts

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