Do those bumps bother you? Here's why you shouldn’t be concerned, and why you should keep your seat belt fastened.

As you walk down the jetway toward the aircraft you’re about to board, are your thoughts consumed by what awaits you at your destination? Or do other things concern you, like turbulence? If you’re a passenger who absolutely hates turbulence, you’re not alone. I don’t particularly care for it either, and I get more questions about turbulence than anything else.

One technical definition of turbulence is the up and down mixing of air currents in the troposphere. The troposphere, where all of Earth’s weather occurs, is the lowest layer of the atmosphere. It starts at the surface of the earth and goes up to the stratosphere; the thin layer that divides the troposphere and stratosphere is called the tropopause (“trop” for short). The trop varies in height from about 26,000 feet during the winter months to approximately 42,000 feet in the summer (higher at the equator and lower at the poles).

If you observe where a thunder cloud flattens out at the top, that’s a good indication of the trop’s location—the height of the trop varies depending on atmospheric conditions. Because most airliners cruise between 28,000 and 43,000 feet, we routinely fly through the trop, and therein lies the problem: The rapidly changing temperatures and strong wind shears cause the turbulence we feel.

The flight plans that most pilots follow annotate the height of the trop along the route of flight. This is important data, because the trop may be lower than the planned flight altitude, higher, or a combination of both. The airplane I fly is climb-limited after takeoff because of the amount of fuel we carry. If we’re limited to 29,000 feet as an initial cruise altitude, it’s very likely we’ll intersect the trop somewhere during our flight. However, when the trop is at a much higher altitude, the plane will never climb enough to encounter the bumps.

Turbulence also frequently occurs in the vicinity of convective activity (i.e., thunderstorms) and can be seen via the aircraft weather radar. This new radar is very accurate—it can detect multiple layers of thunderstorms and even see turbulence when it’s associated with detectable precipitation (i.e., rain). The radar uses the Doppler effect (a change in the frequency and wavelength of waves) to measure the velocity of raindrops moving parallel to the aircraft’s flight path. This measurement results in a uniquely colored indication on the pilot’s radar displays.

Generally, avoiding convective activity is the preferred method for sidestepping this type of turbulence, but avoidance is not always possible. Using radar, pilots pick the spot in a line of thunderstorms that shows the smallest amount of precipitation, then fly through that point. There will be turbulence associated with this technique, but it is often the only way to keep the flight on schedule.

Unfortunately, there is a type of turbulence that the radar cannot see: the absence of precipitation, known as CAT (clear air turbulence). Most CAT events occur in the area of a migrating jet stream or near mountains, where the air is forced up vertically. The jet stream is a narrow stream of wind that travels from west to east and varies in intensity and location depending on the time of year. The jet stream is generally lower in latitude. It can pack winds up to 250 miles per hour, with the strongest winds in winter. The jet stream tends to twist and turn as it makes its way around the globe, and some of those turns can be abrupt.

I vividly remember this encounter with the jet stream: I was coming back from Tokyo, where the jet stream turned a 90-degree angle in a confined area. This anomaly had been forecast for that evening’s flight, so we did have prior warning, but it was still a shock when we went from having 190 knots of tail wind to less than 50 knots in less than 30 seconds. Luckily, the turbulence was short-lived, and we had seated the passengers and flight attendants in anticipation, so there were no injuries or incidents.

Another form of CAT is wake turbulence, or a vortex disturbance off of the jet’s wings and engines. This type of turbulence cannot be seen, but it may result in short but violent encounters. When contrails (condensation trails) are visible and the plane is at altitude, it’s possible to see the swirling effect that the engines have on creating this type of turbulence. Smooth or choppy contrails can also indicate calm or troubled skies.

In addition, pilots use information passed along by other pilots during the flight in the form of pilot reports, or PIREPS. When flying in international airspace, pilots monitor a common radio frequency and share information about turbulence and wind with every other airline, regardless of nationality.

While no one likes to fly in turbulence, we must respect the reality of it. Hundreds of injuries to flight attendants are reported each year because of turbulence-related events.

My advice? Pay attention to the “fasten seatbelt” sign, and always follow crew-member instructions. Keep in mind that airliners are built to endure stresses far greater than any turbulence you’re likely to encounter. While you may get bumped around a bit, rest assured that you’re safe, and your pilots are doing everything in their power to provide you with the smoothest possible ride.
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CHRIS COOKE is a pilot with a major domestic carrier. He can be reached at editor@executivetravelmag.com.