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QUESTION: Hello, nice to meet you and I'm sorry for disturbing!

I would like some help from someone with a great experience like you. I'm a private pilot, heading towards my commercial license and I realized that I have some doubts regarding some flight regimes which I don't master on my own. I will try to summarize them below, I hope you could follow and help me.

The first issue I have is about stall and spin in bad weather/turbulence. For example, if suddenly the 15 kts headwind shifts its direction and becomes a tailwind, I will lose 30 kts of airspeed, right? If so, I don't get it if the result would be a stall or just losing lift and momentary have an increased rate of descent. Actually, I can't figure out on my own if the AOA would change even if the pilot maintains the same attitude during the windshear event.

The same problem for updrafts/downdrafts. As far as I know, these gusts momentary change the AOA and thus it would results a stall, right? What if hypothetically just one wing is affected by the gust? The result would be a spin? Or more likely a snap roll? All these scenarios are in the low and slowflight regimes i.e. takeoff/landing, because I guess this would be the most probable scenario to be problematical.

The next problem is about crosswind landings. We use to make stall landings in small airplanes, so, considering this and a kicking-the-crab in flare technique, you are uncoordinated close to stall when you kick the crab and use opposite aileron to prevent banking due to rudder use. How safe is this?

Also regarding stall, is there any difference between an accelerated stall and a dynamic one?

Thanks so much!

ANSWER: The first issue I have is about stall and spin in bad weather/turbulence. For example, if suddenly the 15 kts headwind shifts its direction and becomes a tailwind, I will lose 30 kts of airspeed, right? If so, I don't get it if the result would be a stall or just losing lift and momentary have an increased rate of descent. Actually, I can't figure out on my own if the AOA would change even if the pilot maintains the same attitude during the windshear event.

answer: windshear is a difficult scenario to discuss since there are many variables associated with its encounter and successful recovery.   The number one key to recovery is avoidance.  Knowing flying into a known windshear condition is not a smart idea.  there are many books written about how to avoid windshear and you can also ask your instructor to review the factors to be assessed.  

But As a commerical pilot you need to be constantly aware of the factors related to the production of windshear and be constantly vigalent when operating your aircraft.  If windshear is suspected you need to increase the available energy in your aircraft.  Energy is equal to a combination of altitude and groundspeed.  If you suspect a 15 knots decrease in headwind immdediately followed by a 15 knots increase in tailwind (a 30 knts decreased performance shear), you need to increase your Vref speed on approach equal to half the steady wind state of the shear (15knots) + the speed of any known gust.  On approach you don't have much energy in your altitude so groundpseed is all your have to store the needed energy.  As you get closer to touchdown you will need to reduce that stored energy by reducing your speed once you have passed through the suspected windshear area.  If you encounter unexpected windshear on approacg condcut a missed approach and wait until the windshear passes ot go to an alternate airport.


The same problem for updrafts/downdrafts. As far as I know, these gusts momentary change the AOA and thus it would results a stall, right? What if hypothetically just one wing is affected by the gust? The result would be a spin? Or more likely a snap roll? All these scenarios are in the low and slowflight regimes i.e. takeoff/landing, because I guess this would be the most probable scenario to be problematical.

answer: the first part is right.  Whats called a microburst can cause a momentary increase in AOA and a stall could occur.  But since the aircraft is moving forward at over 100knts you will pass through the microburst fairly quickly.  Microburst happen in somewhat predictable areas and cloud types so your knowledge will help you be ready as per my first answer.  Up and down drafts are not that small and defined as to effect one side wing and not the other. So it is unlikelt that it would cause an aircraft to spin.  Wake turbulence is more likely to flip a light aircraft over.  When operating in a low energy condition close to the ground as in takeoff and landing you need to very careful not to operate into an area of windshear.  delaying the takeoff or landing is always the wisest choice.

The next problem is about crosswind landings. We use to make stall landings in small airplanes, so, considering this and a kicking-the-crab in flare technique, you are uncoordinated close to stall when you kick the crab and use opposite aileron to prevent banking due to rudder use. How safe is this?

Answer: stall landings have been proven as unacceptable for the very reason you stated.  It is important to use a Vref speed which provides a margin over the stall speed for landing.  if you are uncomfortable using the technique you mentioned then use the forwrd slip method by holding a wing into wind while using the rudder to maintain the aircraft centerline on the middle of the runway. This method allows you to establish the correct attitude to prevent drifting close to the ground.


---------- FOLLOW-UP ----------

QUESTION: Thank you very much, if you don't mind, I have a stupid question: have you ever noticed on small GA planes that the yoke moved on its own in turbulence?

Answer
Not sure what you're referring to with this question.  I have seen light aircraft yokes move due to external gusts which is normal since the flight controls are light and subject to such things.  This would not be unusual in any aircraft.  In larger aircraft we use dampers to reduce the effect.  

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Kevin Parker

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I will do my best to answer any question related to my experience. If I don't know, I promise to help you find the answer. Every question deserves an answer.

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I have 30 years experience in Commercial Type Rating training, program development, human factors, instructor training, flight simulation and flying large aircraft in general. Operated L188, DC8, B747, B757, A320, A330 and A340 aircraft. Involved in cockpit design, flight testing and type certification.

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