Ask a Pilot with Spencer: What is Clear Air Turbulence?

In our Ask a Pilot series, pilot Spencer Marker answers one of your aviation-related questions each week. See past installments here and submit your own to Whitney@johnnyjet.com.

The question

During my last (very scary) flight we experienced about an hour of “clear air” turbulence, or at least that is what I think it was because nobody of the crew explained what was going on. I am a very nervous flyer and after that flight even more so. So this is my question: What exactly is clear air turbulence and is it normal to last an hour on a two-hour flight?

—Giorgina

The answer

Hey Giorgina, thanks for writing in to be featured in this week’s Ask a Pilot. Clear air turbulence (or CAT) is a nuisance to not only our passengers, but the flight crew, as well. As the name implies, clear air turbulence leaves no visual cues of its presence, and therefore, is challenging for pilots to predict. However, using the tools at our disposal, we are always working to avoid it and provide the smoothest ride possible to our passengers.

What exactly is clear air turbulence?
Like I’ve stated above, clear air turbulence is an all-encompassing term for turbulence whose presence isn’t indicated by clouds or some other visual signal. It may be encountered near the jet stream in the winter, while flying over mountains, or near strong frontal systems. As you’ve indicated, an encounter can last a few seconds or an hour or more, depending on the type of atmospheric phenomenon the airplane has encountered.

The jet stream is like a river of fast-moving air that meanders around the world. In the United States, the jet stream starts over the west coast and wiggles its way east. During the summer months, the jet stream stays north while warmer temperatures prevail. But in the winter, the jet stream strengthens and slides further south.

During the winter in the US, when the jet stream is strongest, CAT can be encountered on its north or polar side. This is due to the rapid change in wind speed from inside the jet stream’s core, to outside. We call this sudden change in wind speed wind shear.

As air circulates through the atmosphere, it moves in different directions and speeds. For the most part, changes to these wind speeds or direction are gradual. However, with the wind shear encountered with a jet stream, the change is sudden and can cause a fairly bumpy ride.

Flying over the mountains can also cause CAT. Most commonly, this type of turbulence, called mountain wave turbulence, gives little or no indication of its presence. Instead of bumping an airplane around, like a car driving on a gravel road, mountain waves feel like a spirited drive on a hilly road. The waves can cause unintended changes in altitude of 100 feet or more.

Avoidance
So, how do we avoid turbulence? For most encounters with CAT, a change in altitude will almost always alleviate the bumpy ride. Especially at high altitude, as the wind shear is often limited to a few thousand feet in the atmosphere.

Pilots encountering a rough ride will notify Air Traffic Control of the bumpy conditions and receive clearance to a smoother altitude. Their report (we call this a PIREP, or pilot report) will be forwarded to other aircraft in the area. This way, other pilots can be warned and take action before they too encounter bumpy air.

Additionally, with the introduction of tablet computers in the flight deck, pilots now have access to real-time turbulence information and can often avoid an area of rough air by changing altitude before it is even encountered.

Despite a pilot’s best effort, there are those days where we just cannot find a smooth altitude. So an encounter like yours is not uncommon. In these instances, we turn on the fasten seatbelt sign, inform our flight attendants to take their seats and slow the aircraft down.

And, while a bumpy ride is uncomfortable, turbulence poses very little risk to aircraft that encounter it. Airplanes are designed from the start to withstand the stress of the roughest air. Check out the video below from Airbus to see exactly how much stress a jetliner can handle.

Instead of turbulence being a hazard to the airplane, the true hazard of a bumpy ride comes to the occupants inside the cabin not being in their seats with their seatbelts on when it’s encountered. So please, if the crew asks you to be seated or the fasten seatbelt sign is on, return to your seat and buckle up.

To sum up
Thanks for writing in this week, Giorgina! You pose an excellent question. While encounters with any type of turbulence can be uncomfortable, the duration of clear air turbulence can make it unbearable. That being said, your flight crew is always trying to find the smoothest ride possible for the given conditions and airplanes are designed to withstand the stress of a bumpy ride. So while it might be uncomfortable, flights through extended periods of turbulence are still perfectly safe.

Thanks again for the question! Have you heard the famous Airbus “barking dog”? Share your stories below! And if anyone has a burning aviation question or something you would like cleared up, drop us a line at Whitney@johnnyjet.com to get your question featured in an upcoming Ask a Pilot column.

Tailwinds,

—Spencer