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The drink spiller, bag shifter, overhead bin opener, food tray clutcher and barf bag filler; what am I talking about? Yes, you guessed, it turbulence. It is something experienced by most travellers and even the most seasoned traveller can be unsettled by this thing that turns up unexpected and gives you a good thrashing at 37,000 feet. In this segment of ask the pilot I want to explain what turbulence is and to knock back that fear factor produced by the nervous traveller who gets off a flight and says. "It was the worst turbulence I have ever experienced we must have gone up and down 2,000 feet in a minute”.

First off turbulence is all around and can be seen in many different things, to give you a visual let me describe it this way. Smoke rising from a cigarette is turbulent flow, for the first few centimetres, the flow is certainly straight, known in flow terms as ‘laminar’. Then smoke becomes turbulent as its velocity and characteristic length are both increasing. In much the same way, a formula one car can find it difficult to follow the car in front through a fast corner due to turbulence created by the leading car, which has the effect of causing less down force which reduces grip.

One of the main types of turbulence that you experience in an aircraft is called Clear Air Turbulence otherwise abbreviated as CAT. CAT is the turbulent movement of air masses in the absence of any visual cues such as clouds, and is caused when bodies of air, moving at widely different speeds, meet.

The atmospheric region most susceptible to CAT is the high troposphere at altitudes of around 7,000–12,000 metres (23,000–39,000 ft) as it meets the tropopause. Here CAT is most frequently encountered in the regions of jet streams. At lower altitudes it may also occur near mountain ranges. Thin cirrus clouds can also indicate high probability of CAT.

There are times where we can predict areas of turbulence such as the fluffy cotton ball looking cumulus clouds, particularly the anvil topped ones that occur in conjunction with a thunderstorm, mountain ranges, when flying through certain frontal boundaries and transiting a jet stream boundary, all of these will definitely give you a good old bumpy ride. Unfortunately there are those times that you can't predict and we get that unexpected turbulence. Like most things turbulence doesn't show up on radar. We can see weather fronts on radar to avoid areas more likely to be turbulent but our best source of information is from real time reports from other pilots. When we give reports we grade turbulence from light to extreme. I have several pilot friends who have 10'000 + hours and have never had to report extreme turbulence. Pilots are more likely to report light to moderate, and in reality severe turbulence is something the average traveller will never experience in his lifetime.

I will say for fearful flyers, the screamers the chair grippers and nail bitters, a plane cannot be turned upside down, it's wings won't break off, nor the tail, in other words the aircraft will not be thrown from the sky by even the biggest, gustiest air pocket. Conditions may not be the best nor the comfiest but the plane will not crash from turbulence.

As pilots we will often request a different altitude to get out of the turbulence, this is not because we are worried, it is to make it more comfortable for our passengers. If we suspect we will be in and out of it, in a short amount of time, we will ride it out but sometimes this can't be done and we have to stay in turbulent air for extended periods.

Contrary to what passengers think we pilots are not up there panicking gripping the yoke for dear life, saying “Oh God Bob, do you think she'll hold together? You get your hands on it too, we need all the help we can get.” Quite the contrary, we are quite calm we know the wings are not about to drop off, we see it as nothing more than an inconvenience, our main concern is letting our passengers have as comfortable a flight as possible and keeping food and drinks where they belong and not in your lap. Planes are built to takes some massive loads and forces in both positive and negative G's. They have very high stress levels before anything would happen, even the most seasoned pilot with thousands upon thousands of hours will never see enough turbulent air to ever bend a wing let alone snap it off.

Another fabrication I want to address (and let you all in on a little truth) is what I mentioned earlier, the exaggerating traveller. "It was the worst turbulence ever we must have gone 2,000 feet in a minute." This may be what it feels like, but it is totally untrue, you would be lucky to move around 10-20 feet, in moderate to severe turbulence you might see as much as 40 feet and the worst I have heard from one of my pilot friends was he moved 100 feet. The turbulence you feel would be usually just the 10 - 20 foot, it feels worse but being in the cockpit I can see that my altitude, bank and my pitch barely move they just sort of flicker a little bit.

In conclusion when you are next on a flight and experience turbulence, don't worry, we will be fine and I am doing my best to get you out of it so you can enjoy your dinner service. For those with queasy stomachs I am sorry I can do nothing to stop you grabbing the bag but I will have you out of it soon.

So until next time enjoy the article and don't forget if you have a question just ask the pilot.

....and for those of you not convinced on the strength of aircraft wings, check out the test that was done on the Boeing 787 wings.