As you know, the law requires that everyone onboard have his or her seat belt fastened during takeoff and landing, and when told to do so by the captain. Once a flight reaches its cruising altitude, severe turbulence is very rare and, as a result, some people unbuckle their seat belts. In our view, that is a bad idea because while we are learning more about weather detection all the time, a phenomenon known as “clear air turbulence” can turn a smooth ride into a rough one very quickly. As its name suggests, clear air turbulence can occur when there are no clouds in sight. It is also invisible to aircraft radar.
Generally speaking, turbulence takes place when winds of different speeds, directions, or temperatures come into conflict with one another. While storms are generally easy to avoid, the turbulence caused by winds on the fringes of a storm is harder to spot. Winds such as these are one cause of clear air turbulence. Another is wind swirling around mountain peaks, which interrupts wind flows and creates an undulating effect known as mountain-wave turbulence. A third source of unexpected turbulence is conflict along the tropopause, a thin layer of air that divides the troposphere — the lowest atmospheric level, where most weather disturbances take place — and the stratosphere, which is generally more stable. Interestingly, when you see storm clouds flatten out at the top, it is usually because the updrafts of the storm are bumping up against the bottom of the stratosphere. Pilots know it’s wise to be alert to the possibility of bumpy air when passing through the tropopause, which is located at an altitude of around five miles in the winter, eight miles in the summer, and as high as 11 or 12 miles in the deep tropics.
By studying information from weather balloons, pilot reports, and the output of National Weather Service computers, meteorologists can spot conditions that might cause turbulence. Unfortunately, pinpointing its existence and exact location is beyond our current capabilities. The best source of information about clear air turbulence is reports from pilots who encounter it. However, because turbulence is often short-lived, anything short of instantaneous communication may not be effective.
Whenever our pilots know there’s bumpy air ahead, they turn on the seat-belt sign and do their best to avoid it. But despite our best efforts, we still run into clear air turbulence from time to time. When that happens, people can be injured, and most passengers who are hurt do not have their seat belts fastened. That’s why it makes sense, always, to keep your belt fastened loosely across your lap. It’s not the least bit uncomfortable, and you will be much safer should your flight experience an unexpected patch of rough air.
As a pilot, I know that clear air turbulence, though very rare, is also very serious. So when I’m riding as a passenger, I make sure I keep my seat belt fastened at all times. I would feel uncomfortable without it, and I hope, after reading this, you will feel the same. So, if you’re not already buckled up, please fasten your seat belt. Then sit back and enjoy the trip. Thanks for flying with us today.
GERARD J. ARPEY
Chairman & CEO