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Home > Air Turbulence > Flying in turbulence…
Flying in turbulence…
Weather - Air Turbulence
Sunday, 03 January 2010 10:38

Dear Capt Lim,

Thank you for this amazingly informative and helpful site. Even though I have studied some fluid mechanics and some of the information is familiar, I have learned many things from a pilot's real-world perspective that I wish I knew much earlier.

We recently flew AS860 (12/31/09) from HNL to SEA. The turbulence was the worst I'd ever experienced, featuring some of the unpleasant side-to-side motion that you have talked about before, and causing major spillage from a beverage cart -- though I guess the turbulence would be classified as moderate to severe, not extreme. I was frankly amazed that the pilots could maintain controlled flight. It was enough to give me some anxiety about flying -- something that I've never had in the past 40+ years of routine air travel.

This recent experience made me wonder about some things. Pardon me if you have covered these in your Turbulence FAQ, but after reading the whole FAQ I didn't see these addressed exactly -- perhaps I missed them.

1. As a pilot, how do you control the stick and pedals when your whole body is being violently thrown around? While this isn't a factor for the autopilot, I think you mentioned before that in bad weather, the pilot sometimes takes over. That would seem extraordinarily difficult, physically and mentally.

2. Even on autopilot, the captain and/or co-pilot presumably needs to monitor what's happening and be ready to take over. That said, how does a pilot maintain a sense of orientation and focus when the plane is being violently tossed about on all 3 axes?

3. I was surprised to hear that it is customary to reduce power before entering turbulence. It makes sense, but isn't there a danger of a stall condition (especially if there happen to be strong tailwind gusts) or some type of lateral movement or rotation that puts the plane in an unflyable position? That is always my biggest worry.

4. Does the autopilot "know" enough to reduce power when flying into turbulence?

5. From what I can infer, the pilots on our plane did an outstanding job of seeking and finding a smoother flight level. About what percentage of the time does this approach -- seeking a smoother flight level -- actually work to alleviate the turbulence? Is there a particular method involved (eg first go up, then down)? It would help to know in advance what to expect.

6. Can the autopilot automatically seek out a smooth flight level as well, and is it effective at doing so?

7. Is there any way to look up how the pilots of our particular flight classified the turbulence we experienced that day? I would like to get some perspective on what we experienced. I think different people on the flight would have different opinions on whether walking and food service would have been possible (in practice food service was suspended).

8. I see that you flew the 777. Mostly I wind up flying on 737s -- typically the -800. I'm assuming that this model (with 40+ years of service, 10+ as the -800) is also capable of handling severe turbulence as well as any other airplane, but could you please confirm that?

Thanks in advance for any and all answers -- they will greatly ease my anxiety. I would also like to have an answer when a family member worriedly asks "What's happening?" -- as happened on my aforementioned flight. All I could manage was a weak "just hang on," but with your help I can be calmer myself and more helpful to my family. I'll give you due credit for the information of course. alt And if you choose to post this Q&A publicly, I hope other readers will benefit as well.

RM

Hi RM,

1. A pilot is trained to handle the plane manually when the autopilot is disengaged to cope with turbulence. It is not that difficult after all. Remember, the pilot is securely fastened with his seat belt and he is never thrown violently around in turbulence!

2. To cope with being tossed around the three axes, there are sophisticated flight instruments in the cockpit to guide the pilot along.

3. Power is reduced slightly to fly a recommended turbulence speed to minimize the stress on the airplane structure just like you would reduce the speed of your car as you approach a road with lot of potholes or else you have to change your suspension!

4. The “autopilot” does not know when to reduce the power when encountering turbulence. The pilot has to program the computer to fly at a lower speed or he can intervene by taking over and reselect a slower speed manually. In fact, it would be the auto-thrust that adjusts the power automatically when the speed is reduced.

5. Normally, the pilot would check with the air traffic controller or other planes ahead to find a more comfortable level before requesting for a climb or descent.

6. The autopilot will fly the plane according to the pilot’s program on the computer and it does not know where the smoothest flight level is unless it is directed to fly to such a level.

7. Even though a pilot is briefed on the turbulence along the route he is flying on, there are times when it is not possible to determine its severity, especially in clear air turbulence. To be safe, I always advise my passengers to be securely fastened with the seat belts when they are seated even when there is no turbulence. As you have said, different people react differently to turbulence… a little jolt may be considered as severe to those faint-hearted!

8. Yes, I used to fly the Boeing 777 (now the Airbus A320/A340) and the Boeing 737-800s handle turbulence just as well. Like it or not, turbulence is never pleasant in any planes! I have mentioned this many times before; the turbulence a pilot is generally able to navigate through can be said to be an issue of discomfort rather than one of safety to be feared of.

Wish you safe flight always and Happy New Year 2010 to all! alt

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Flying in Turbulence...
Dear Captain Lim,

Thank you so much for the comprehensive and reassuring reply. I appreciate your providing this great public service despite what is clearly a demanding schedule.

Your response helps clarify a lot of things and for that I am grateful.

Based on my limited knowledge of physics and the atmosphere, and building on what you have said, I'd like to offer a few further thoughts that might be of encouragement and clear up some misconceptions for fellow air travelers. See if you agree with these.

• Air in the atmosphere (even in the major storms that pilots can detect and avoid) typically does not move very fast, vertically, compared to a modern jet airplane at cruise. In fact, if you were just standing still in a "turbulent" area the updraft or downdraft is typically a few meters per second -- like riding an elevator in a tall skyscraper.

• Even horizontal shears, though more pronounced at times, are minor compared to cruising speeds. A hurricane force wind or tornado could hit 200+ mph, but even in that extreme and avoidable case, compare that to a jet going 500+ mph.

• The reason turbulence seems to buffet the plane is because you are moving fast horizontally, so you are rapidly entering and exiting these areas of changing wind. The relative speed differentials encountered are small compared to the airspeed of the plane.

• At cruise you are not feeling any acceleration, even though you're moving fast. This is Newton's second law. So even if the plane is bumped around, these are really minor deviations from a fairly straight trajectory. You feel differently in your seat because all you feel is acceleration, not velocity, and there is no nearby lane marking or other object to give you some reference.

• I went back and looked, and confirmed that no modern large jet airliner has ever crashed due to turbulence, as I think you have stated before. Inattention to procedures by maintenance crews, airlines, or occasionally by crew seem to be greater safety risks, but even then rarely produce fatal accidents.

• Modern airplanes and control systems are amazingly resilient in recovering from difficult situations. Engine failures, holes in the fuselage, stalls and dives -- all can be recoverable situations nowadays given good maintenance and attention to procedures and training.

• In contrast to our daily lives, getting on a plane involves relying on someone whom you are not qualified to replace. You also don't get much information or have much context when sitting in the cabin, and you don't have the alternative of just getting off. This is the real anxiety producer. Arming yourself with knowledge is key.

Your website, Capt Lim, is a huge help in giving people information about flying.

Thanks again for your great public service, happy new year, and many safe travels to you also.

RM
RM , 06 Jan, 2010

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