Insights

Do you know the real meaning?

Consider the word scattered as it applies to cloud coverage. An inexperienced pilot might say, "It's a great day for flying; only scattered clouds are forecast."

Scattered clouds means cloud coverage of three-eighths to four-eighths of the sky; four-eighths is 50 percent. To demonstrate this do the following: Get two sheets of paper that are the same size but different colors--blue and white are perfect. Cut the white sheet in half, and tear one of the halves into silver-dollar-size pieces. Arrange those pieces on the blue sheet of paper so that none of the pieces are touching. That's four-eighths scattered cloud coverage. Are you sure that you want to go flying?

Area forecasts use the word scattered to define thunderstorm coverage. There, it means that 25 to 54 percent of the sky may be affected. That's a bad situation--weather-radar-equipped airplanes excepted.

Consider the term slight chance of thunderstorms, which is used in the convective outlook forecasts. That means a slight chance of severe thunderstorms, wicked storms that must be avoided by 20 or more miles. It does not consider less intense thunderstorms.

Severe turbulence is another example. During a student pilot's final stage check, I ask several questions regarding cross-country flight operations.

Question: What is your first consideration after you level off at cruise altitude on a cross-country flight? Answer: I check my groundspeed as soon as possible in order to validate the winds-aloft forecast.

Question: Why is that important? Answer: Fuel consumption and reserves for the planned flight.

Question: During the flight, are there other resources that you should use? Answer: Yes, en route flight advisory service (radio call sign--Flight Watch) for weather updates and pilot reports; and hazardous in-flight weather advisory service (HIWAS), which broadcast airmets, sigmets, convective sigmets, severe weather watch bulletins, and air route traffic control center weather advisories over designated VORs.

Flight Watch tells you that a Beech Baron reported occasional severe turbulence over a point that's 40 miles ahead of your current position. What should you do? Most students say turn around and go back home. Sorry, that's OK considering their experience, but it does not reflect practical knowledge.

What is occasional? One-third of the time. Intermittent is two-thirds of the time; continuous is more than two-thirds.

How do you define severe turbulence? The airplane is momentarily out of control. What is extreme turbulence? That's when the airplane is totally out of control. During 47 years of flying, I've never experienced extreme turbulence. To me that implies an encounter with thunderstorms or rotor clouds located on the leeward side of mountains during strong wind conditions. Thanks but no thanks.

Most pilots eventually encounter severe turbulence where the airplane is momentarily out of control, but the pilot can readily regain control. Sudden rolling or pitching actions are two examples that occur frequently.

No, you can't turn back. What are you going to do? Answer: As I approach the area, or at the onset of light to moderate turbulence, I'll reduce to maneuvering speed, VA. Why do that? Answer: So that if the G-load reaches the allowable load of 3.8 Gs for my Normal category airplane, the wing will stall and structural damage will not occur.

Why don't you extend your flaps in that situation to help stabilize the airplane? Answer: Because that's insane. With flaps extended the allowable G-load decreases to 2.5 Gs or less, and I would grossly compromise the airplane's structural integrity. I'm always shocked when someone tells me that flaps extension in such a situation seems reasonable.

The vocabulary of the aviation world is complex, and it requires complete understanding and proper usage. For your own safety and the safety of others, make certain that you know exactly what each word or phrase means. Your professionalism will be noticed.

Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying since 1959 and has 25,000 hours in fixed- and rotary-wing aircraft. Visit his Web site.