Flying Seasons

What to do in tooth-shattering, head-banging turbulence

Soon the spring season will come pounding its way to your area, shaking you free of evil winter — evil, that is, except for skiing — and leaving turbulence in its wake. Quick, what's your power setting for maneuvering speed (V _A)? You know about V _A, the speed that helps protect the airframe from structural damage, right? You could look it up if you could read the pilot's operating handbook between bounces. Knowing the power setting can replace inaction or a slow reaction with a quick response.

On a calmer day, find the maneuvering speed given in the pilot's operating handbook, and look at the power chart to see what the setting should be. Memorize it, or make your own customized checklist and add it under emergency procedures.

It's a good power setting to know in any season, especially if you fly IFR and are wondering whether to go through or around that innocent-looking cumulus cloud up ahead. Think of clouds as looking like the dust kicked up after driving over a pothole. The power setting also is handy if you think there is even a small prospect of entering an embedded thunderstorm.

Weight issues

That speed will not necessarily safeguard you and the airplane, of course, since it is published for maximum gross weight conditions. When was the last time you flew at maximum gross weight? As you remember from your training, lighter gross weights mean you must fly more slowly than V _A. In a Cessna 182, that means you need to fly almost 20 knots slower than maneuvering speed when light. Cessna Aircraft offers speeds at three different weights as guidance.

Some aircraft manuals publish only a single speed for V _A, so does that mean you have a super-powerful machine, sort of a roboplane that can fly faster than most aircraft in turbulence? It probably means instead that you have an older aircraft with a flight manual that was typical of its time and did not include suggested slower speeds at lighter weights. Some manufacturers even today do not include turbulence speeds for maneuvering at lighter weights, but just know that if you are alone in the aircraft without baggage and with half-full tanks, you'll need to be slower than V _A when the going gets rough. There are great little rules for determining exactly how much slower you need to be, and generally they are rules you are never going to remember. The important thing is to slow to V _A quickly using a memorized power setting, and then think about whether you are lighter than max gross weight. If so, reduce it some more — 10 to 15 knots is a good place to start.

Waiting games

The important thing is to slow down quickly, instead of waiting to see if the turbulence gets worse. Even the strongest airplane can get wrinkled, as a student and an instructor found out in Florida in March 2005, according to a report in the AOPA Air Safety Foundation accident database (see " Safety Pilot Landmark Accident: Working a Hole," June 2006 Pilot). The controller had warned there was no way to get to the destination without going through weather, so the instructor told controllers that in that case, he just wanted to avoid cells. No cells were on radar when the aircraft, a Cessna 172S, encountered turbulence and heavy rain. The accident report does not say if the aircraft was slowed by the pilot, but a good decision was made to turn 180 degrees and get out of the stuff, as we were all taught in ground school. Too late, though, because the turbulence broke the door hinges on the copilot's side and ejected the copilot window into the wind stream, where it was carried to the tail and bent the horizontal stabilizer down at a 30-degree angle. The airplane landed safely.

There's another reason to slow to maneuvering speed; maybe you and the airframe are in no danger and can ride out light turbulence, but your passengers may have a different concept of comfort. They've wondered since takeoff why there are no in-flight drinks or cheap peanuts, and they expected the same ride as their last airline trip where the captain changed altitude three times to find smooth air.

Although slowing down is the general idea, there are times to speed up, such as when using a higher-than-normal approach speed in gusty conditions. That doesn't mean that the rougher the conditions, the faster you go on short final approach. Here's what the FAA says: "In gusty air, no more than one-half the gust factor should be added. An excessive amount of airspeed could result in a touchdown too far from the runway threshold or an after-landing roll that exceeds the available landing area." If conditions are that windy, there's an excellent chance your groundspeed will be low and erase any worries about rolling off the end of the runway, assuming you touched down in the first third of the available runway. If what you see out of the windscreen is greater than your capacity for excitement, go around.

Terminology tuneup

I'll readily admit that the last time I made a turbulence report to a controller, I asked for an altitude change because I said I was getting "beat up." That wasn't the terminology suggested in the Aeronautical Information Manual, although it did alert the controller to turbulence in his sector and won me an altitude change. An Internet link at the bottom of this article will take you to the correct AIM terms for reporting turbulence. Do you report all light turbulence as "light chop"? Did you know there is also "moderate chop"?

Looking at the AIM information, there is both light turbulence, which causes momentary changes in attitude or altitude, and light chop — which is similar in intensity but doesn't cause altitude and attitude changes. It's just annoying. Then there is moderate turbulence, which is similar to but stronger than light turbulence, and moderate chop, which produces rapid bumps but does not disturb attitude and altitude — although it may disturb your personal attitude. As you know, a pilot report from a large aircraft of "light chop" probably means "moderate chop" to a smaller aircraft.

You don't have to sit there and take it, of course. If you are talking to controllers, ask them for reports of flight conditions at other altitudes and request to climb or descend. Or, if you are not talking to controllers, call up flight watch and ask for pilot reports.

Finally there is severe turbulence and extreme turbulence. Extreme turbulence means you can no longer control the airplane, as was the case in April 2005 when a Mooney was literally sent spiraling out of control above Nebraska, according to another report in the AOPA Air Safety Foundation database. The aircraft descended 10,000 feet in instrument conditions, finally entering VFR conditions, where the pilot made a recovery, and what a recovery it was. The pilot pulled 12 Gs, bending the right wing spar, wrinkling the skin, and damaging the down-link on the landing gear, which then collapsed after a safe landing and short taxi. It wasn't the downdraft that bent the airplane — it was the recovery — but that's another story.

With severe turbulence, you are out of control only part of the time (lucky you!), but there is no additional designation of severe "chop." Forget chop — you've got the real thing. Your passengers are miserable, and it's time to spend an hour or two at the nearest airport exploring all the selections of the FBO's vending machine, or amusing them with a ride in the loaner car. In other words, wait it out on the ground. If you are in extreme turbulence, you are most likely out of control most of the time. But those are the days you elected not to take off in the first place, right? That probably ruined their entire weekend, but you still have your wisdom teeth intact rather than fracturing them on the rocky airways above.

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