Turbulence can mean a lot and, sometimes, not so much

Safety first

Posted: Friday, July 13, 2001

Most pilots realize early on that if the passenger gets a good, smooth landing, they perceive the whole flight as being comfortable.

I work in the Juneau Airport Terminal and hear comments about flights by passengers every time I go through the lobby of the airport. Arriving passengers being met by family or friends are frequently asked, "How was your flight?"

The usual response that I hear is about the smoothness of the en route portion or the landing. Most pilots realize early on that if the passenger gets a good, smooth landing, they perceive the whole flight as being comfortable.

During the summer months, however, the lobby chatter tends to dwell on the turbulence encountered on the flight. Pilots of large aircraft do the best they can to avoid turbulence. One way that they can avoid turbulence is to try different altitudes where there is smoother air. Smaller aircraft that fly at lower altitudes can avoid terrain that can generate known turbulence.

Avoiding something that can't always be seen is not an easy task.

Turbulence simply stated is unsettled air. When I was young I was fortunate enough to travel by air frequently. I am probably dating myself but at that time turbulence was referred to as "air pockets." Holes in the air? Perhaps it's a vacuous atmosphere allowing the plane to fall? That's what people thought, I guess. Some still think of turbulence that way.

The truth is that turbulence is created by many different factors. Low level turbulence is most frequently caused by surface heating, mechanical factors such as buildings, trees or terrain, convective lifting, frontal activity and aircraft wake turbulence. Clear air turbulence, which strangely enough happens in clear air and can't be anticipated, most often happens at high altitudes, over 15,000 feet, where intersecting layers of air meet.

Turbulent air can also be seen by the effect it has on cloud layers. If the clouds are cumulus - rising and flat on the bottom topped by billowy cauliflower - the chances are that it will be bumpy near those clouds. Air passing over mountains can create flat, lens-shaped clouds that indicate high wind and turbulence in that area. Inversion layers - cooler air that is trapped by a layer of warmer air - can be seen when smog is present. Where the two layers meet there is usually a wind shear effect that causes momentary turbulence when an airplane passes through the boundary layer.

Thunderstorms during the summer months can be a hazard to aircraft flying in the vicinity of those storms. Thunderstorms are developed by the lifting of warm moist air to great altitudes, sometimes as high as 40,000 to 60,000 feet. During the developing stage, huge masses of air are being lifted rapidly to form the easily recognized anvil-shaped cloud. In the dissipating stage, downdrafts, turbulence, wind-driven rain and hail can be felt as far as 20 miles away from the cloud base. Turbulence encountered in a thunderstorm cell is usually severe and can cause damage to the aircraft. Pilots can see thunder cells by the use of radar and can circumvent the storm avoiding damage to the plane and injury to passengers, even at night.

For the most part, turbulence encountered on the majority of flights is light and can be accepted as a matter of course. Moderate turbulence can be uncomfortable as it strains a passenger against the seatbelt, but is not usually dangerous. What disturbs most passengers is the unexpected nature of turbulence. People who travel over bumpy roads that exert far worse bumps, such as off-road four-wheeling or on dirt roads, seldom feel threatened by the "turbulence."

So think of the "air pockets" as unexpected bumps in the road. Keep your seatbelt fastened and have a safe flight.

Patricia Mattison is Safety Program Manager with Juneau Flight Standards

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