Insider Series: A Day in the Life of a Pilot — Things That Go Bump in the Sky
TPG Contributor “Marty McFly” is a pilot for a major US-based airline. In his next few Insider posts, he’ll give you a behind-the-scenes look into what the average day is like for an airline pilot.
I was at an amusement park recently, riding a fairly aggressive roller coaster with my son. As the shoulder harness came down, people on the ride were chatting about how awesome the ride is and how many times they’d been on it that day. The passengers were all faithfully, and happily, assuming a number of things — that the engineers who'd designed the ride had taken into account the fact that all the stresses the ride would be submitted to were within the structural limits of the ride’s components, that the amusement park had properly maintained the ride and that the ride operator, who was not leaving the ride platform, would correctly operate the coaster.
Fast forward a few days and those very same theme park patrons would now be clutching their airplane seats in a white-knuckle death grip as the aircraft they're on experienced turbulence — why is it people will think nothing of the dangers and risks involved in things like roller coasters but still be petrified of a little in-flight shakiness?
There are many different types of turbulence and which one you're experiencing depends on what part of flight you're currently in — it's all basically a result of the air the plane is moving through being disturbed and therefore not flowing smoothly. The easiest way to picture turbulence is to imagine that an airplane in flight is floating in a block of air like a boat on the sea — if the block of air you're flying through is rising and falling, your plane will rise and fall along with it. All in-flight turbulence is caused by air flowing at different speeds or directions due to different factors like the weather, the proximity of the jet stream (which causes wind speed changes), topographical disturbances or temperature changes. All of these things will impact how smoothly the air flows around the globe and, as a result, how smooth your flight will be. Here's a look at five things that'll cause turbulence to happen during your flight.
1. Mechanical Turbulence
This occurs when wind flowing over the ground is disturbed by objects on the ground, like trees and buildings — the stronger the wind and larger the obstacle, the more turbulence you will experience. That's why, on some days, your approach to the airport will be smooth while on others, you'll be rocking all the way to touchdown.
Mechanical turbulence can also be experienced at higher altitudes due to mountains — we refer to this effect as mountain waves, when the wind blowing over mountain ranges gets pushed upward by the terrain, which then pushes all the air above it up as well. The air eventually descends because of gravity before rising again, while higher mountains and higher wind speeds increase the amount of rise and fall and how far downwind the wave will be experienced. Higher and more abrupt waves will cause a more uncomfortable ride, but it's usually pretty short-lived. This turbulence can sometimes be centralized over small areas and therefore be avoided by routing flights around it. When you are in mountain waves, the ride can often result in the feeling of traveling through an air pocket, but what you're really experiencing is the plane falling with the air on the wave.
2. Thermal Turbulence
Caused by air rising due to the heating of the earth, this type of turbulence is strongest at low altitudes and most prevalent during the warmer months. Different types of topographical features can also increase the effects of thermal turbulence. A large forest preserve, for example, will not have much heat rising off its trees whereas the parking lots surrounding the airport will generate more heat than the preserve and, as a result, the plane will get pushed upward by the rising air from the asphalt and concrete. You'll probably notice this most on approach to the airport as the plane flies over large residential areas.
3. Wind Shear
Turbulence due to wind shear can be experienced at all altitudes, and is commonly associated with thunderstorms — it's actually the cause of most of the turbulence you'll experience in flight. The definition of shear is simply a change in direction or speed of air over relatively short distances. Large changes in wind speed (or direction) or changes over short distances will cause greater amounts of turbulence to occur.
4. Jets in the Jet Stream
At cruising altitudes, wind shears associated with the jet stream are the most common cause of clear air turbulence, which is caused by a rapid change in wind speed and direction along the fringes of the jet stream. Winds in the jet stream can exceed 150 mph, while those outside it are significantly lower. This rapid change in wind speed over a very short distance then leads to an uneven flow of air, which results in, you guessed it, turbulence.
Even though weather forecasters can determine where the jet stream is and what the speed of the wind will be, the ride can vary greatly. Clear air turbulence does not show up on weather radar, so pilots rely on reports from other pilots to better locate the bumpy spots. It can last for hundreds of miles and span thousands of feet of altitude so unfortunately, sometimes you have to just put up with the shakiness until the plane gets far enough away from the shear as the jet stream rises, falls or turns from your altitude or flight path.
5. Boomers (aka. Thunderstorms)
Flying through weather systems that are producing thunderstorms can produce bumpy rides as well, even at cruising altitude. Simply put, thunderstorms are caused by large columns of air rapidly rising through the core of the storm while the air outside this core descends rapidly. This churn of rising and descending air causes very turbulent air, which is why planes will not penetrate the core of any thunderstorm.
Although we do fly around storms, the air around the weather system can still be disturbed enough to generate a bumpy ride. The good thing about thunderstorms is moisture rises and falls, which allows weather radar to detect the areas with the most turbulence since it shows the amount of water content in the air. Even though we do fly through areas with a lot of rain, we try to avoid the spots that have large changes in moisture intensity over short distances. As the storms are building, the air above them will often be turbulent, too, as columns of air push the air above it up and down. Pilots will never attempt to land during a thunderstorm, since the extreme changes in wind speed and direction, both vertically and horizontally, can exceed the performance capability of the airplane.
The only real threat to aircraft is turbulence related to thunderstorms at low altitude, known as low level wind shear — fortunately, most airports have wind shear detectors on the ground and aircraft have wind shear detection systems on board that allow us to avoid flying into wind shear while at low altitudes. In addition, wind shear avoidance and recovery are reviewed and practiced during our aircraft training and annual recurrent training both in the classroom and in simulators. Almost all aircraft accidents related to wind shear in modern aviation have occurred due to these types of low altitude wind shear encounters.
So what does all mean to the white-knuckled passenger in the back of the plane? Pilots are constantly trying to make sure your ride is as smooth and comfortable as possible. We will try to find routing or altitudes that avoid jet stream-related clear air turbulence and keep a wide path around thunderstorms. But, unfortunately there are times when the bumps just have to be endured.
The thing to keep in mind is that modern airplanes are engineered to withstand the stresses of even the most extreme turbulence. For example, the B-777 wing can withstand over 150% of its design load limit, which is well beyond even the strongest turbulence you may encounter. The only real threat that turbulence poses to passengers is from objects in the cabin falling from overhead compartments or from fellow passengers falling on them if they've chosen to ignore the seat belt sign — almost all injuries sustained to passengers during turbulence are due to people not being in their seats with their seat belts on.
Aircraft flying through turbulence are in no danger of coming apart in flight unless the pilots are intentionally penetrating a thunderstorm, which they are not inclined to do. In short, turbulence, although annoying, is nothing to be afraid of.
One time while deadheading on a flight that was transitioning some pretty good bumps, I had to put my hand over the top of my drink and stop trying to finish my crossword puzzle as it was too bumpy to fill in the squares. The petrified businessman next to me asked if I was nervous. I told him the only thing I was worried about was if I’d have time to finish the crossword before we landed. He gave me a nervous grin but seemed to relax as I explained why the airplane was bucking around. Pilots want to get home safely to their families as badly as you do. We are not paid enough to do anything that we consider dangerous and we have the tools, training and experience to avoid turbulence that could overstress the aircraft.
Unfortunately, turbulence is sometimes unavoidable. Hopefully the next time you are experiencing a bumpy ride, you’ll remember that it is no more dangerous than driving down a bumpy road or sailing on a choppy sea. Oh, and don’t ignore the seat belt sign. Even though it may be smooth at the moment, the pilots may know about the bumps soon to come.