One at a time:

Quote Originally Posted by Steve Jeff View Post
Regarding my first question, headwind shifts to tailwind, you said 15 kts and sincerely I don't get it why it's so. I figure out that if the headwind will decrease suddenly, there should be a change in airspeed, e.g. 15kts headind changes to 5 kts headwind, if it's suddenly, the airspeed decreases 10 kts. So, why when it suddenly shifts from 15kts to 15 kts tailwind there is no a 30 kts drop?
When a plane leaves the ground, it flies in a mass of air. All the plane senses is it's motion relative to that mass of air. The whole air mass may also be moving, however, all that does is affect the airplane's speed and track over the ground. Example: You are flying South in an airplane at 120 kts, relative to the air. The airspeed indicator reports 120 kts. Now the whole air mass begins moving North at 15 kts. The airspeed indicator still reports 120 kts, however, the airplane's speed over the ground is now 105 kts, 120 - 15 = 105. That is the ONLY way you know there is 15 kts of headwind, the groundspeed changes. Speed relative to the air mass, or airspeed, does not change. Now the air mass begins moving South at 15 kts. The airspeed still reports 120 kts, however, the airplane's speed over the ground is 135 kts, 120 + 15 = 135. Had that change occurred instantaneously, it would represent a 15 kt change relative to the mass of air. So for the sake of discussion, that's what you "could" see on the airspeed indicator if the plane did not react, a 15 kts loss, not a 30 kt loss.

In the real world, even if the change in speed relative to the airmass is instantaneous, i.e. windshear, the airplane reacts. It can't react immediately because it has inertia (although for a light plane, not much inertia). So you may see the airspeed fluctuate slightly, like 3-4 kts. You won't see more because the airplane has already begun to adjust to the new airmass. A 50 ton airplane has more issues in an abrupt wind shear because it can't react as fast and it may be several seconds before it regains lost AIRspeed, that is it's speed relative to the air mass.