Nobody likes to be shaken up in transport, and on planes even less than elsewhere. Many things can make a flight chaotic, and the discomfort of the situation is compounded by the fear that something could go wrong in a means of transport that is still a source of anxiety for many.
Everything’s better when you understand what’s going on, so we’ll try to explain it to you.
There’s no such thing as an air pocket
A popular expression for what sometimes makes you feel shaken up in flight is “air pocket”. To begin with, this expression is totally inappropriate, because there’s no such thing as an air pocket.
When you hear “air pocket”, you immediately think of a hole, something you fall into without being able to control or stop the fall. This is far from the truth.
By definition, the absence of air (i.e. a pocket) doesn’t exist unless you’re in space, but that’s another matter and space flight isn’t yet open to the general public. There’s air everywhere, and air envelops any body in much the same way as a liquid would.
What you’re feeling, which sometimes gives you the impression of suddenly going up or down, is nothing more or less than a change in the airflow around the aircraft, which can be caused by a number of factors.
To stick with analogies, it’s more like driving over cobblestones in a car or sailing through big waves in a boat. The only difference is that when you’re driving or boating, you can see the cobblestones or the waves, and your brain anticipates and analyzes them, so you’re not surprised. In a plane, you don’t see outside phenomena, so you don’t anticipate them, and they surprise you. That’s the difference.
The real explanation for air pockets: when hot air meets cold air
This phenomenon has a totally rational explanation. The first thing to remember if your physics lessons are far behind you is that warm air rises and heavier, colder air sinks.
A plane carried by a current of warm air will therefore tend to climb until it encounters a current of cold air, which will pull it down. This is followed by a slightly abrupt descent of a few meters, which in the scale of the aircraft and its altitude is nothing, but whose sudden nature can be frightening.
We’re talking about a descent, not a fall. There’s always air, the plane is always lifted by its wings (in fact they don’t lift it, they suck it up, but that’s another story), so it doesn’t actually fall but descends sharply for a fraction of a second, which can sometimes seem like an eternity to the passenger, especially if he hasn’t anticipated it.
What about turbulence?
Another phenomenon that can cause shaking is what is generally referred to as “turbulence”. To explain turbulence, we need to understand how an aircraft stays aloft and the role played by its wing.
As you probably know or have observed, an aircraft wing is not “flat” but curved, which can be seen clearly on a sectional drawing like the one below.
Air passing under the wing (on the lower surface) moves more slowly than air passing over it (on the upper surface). This creates a vacuum that “sucks” the aircraft upwards.
That’s why it’s false to say that a plane is carried by its wings: it doesn’t rest on them, but they pull it upwards.
When the wind is constant during the flight, all is well. But sometimes its strength and direction change abruptly, or different air currents meet. This is called turbulence.
When wind speed and direction change suddenly, and sometimes they can change several times in a single second when the aircraft is in an area where several currents meet, the variation in wind speed creates a variation in lift, and the aircraft is either sucked further upwards or less so.. What makes it go up and down.
Once again, there’s absolutely nothing to worry about; it’s just all the more uncomfortable because, once again, the passenger can’t anticipate because he can’t visualize and understand.
Are air pockets and turbulence dangerous for aircraft?
Some people are worried about whether a plane can withstand these shocks. You’ve probably noticed that in flight, the wing doesn’t stay straight but bends. It’s precisely this amplitude of deflection that enables it to act as a shock absorber, perfectly absorbing those sudden ups and downs.
Some people are worried about seeing this phenomenon through the window, but it’s quite the opposite! A rigid wing would break, while a flexible wing would absorb and support.
We invite you to take a look at how Airbus tests the resistance of its A350. For example, the 45m-long wings of an A380 have a clearance of 6.8 up and down (evening 13.6m!).
What’s more, on state-of-the-art aircraft like the 787 Dreamliner, a multitude of sensors detect and anticipate wind changes, calculate their impact on lift, and make the necessary flight control modifications to compensate for them. A bit like a “dynamic shock absorber“
So, are you reassured now?
Image : turbulence in the air by diy13 via Shutterstock
