Wind shear
Can any of the fly-boys out there help me right with this one please:
When you report wind shear to the controller, you report it as either a gain or loss of airspeed and sometimes drift tendencies. So, what exactly do you mean by gaining speed or loosing speed because of wind shear? Take an example - you are established on a 10 nm final at 3000 ft above the aerodrome and down to 1500 ft, you have a headwind of say 50 knots, now al of a sudden as you pass the wind shearline at 1500 ft, the headwind component falls to 15 knots down to touchdown. As you hit 1500ft in your aircraft, what exactly happens ? I guess from my understanding you will overshoot the glidepath (go above it) and the normal reaction would be to reduce power to intercept the GP and you end up slow descending through and below the GP and land short? Is that correct? and my really big question is, what speed (Indicated , True or ground speed)do you lose or gain????
I cannot imagine it to be indicated because there is no change in dynamic pressure when you reach 1500ft, and yes I can see why your grounspeed change ( because of the headwind dropping off ) , but how can that situation change your Indicated and therefore True airspeed? The fact that there is only a change in wind speed and direction alone cannot change your TAS or IAS,can it???? IAS is obviously what you see corrected for instrument error only as far as I can remember and TAS is IAS corrected for temperature and density. So at 1500ft in my example, how does a sudden drop off in wind speed change your TAS or IAS??? I have no problem with the groundspeed bit, as your GS changes by the TAS being corrected for the new wind component, so no problem there. If you report wind shear then to me, do you mean that you either gained or lost groundspeed??? I can see why wind shear is a problem, basically an unstable approach either landing short or overshooting because of the power changes required etc. I guess it comes back to the age old question again of using either power or elevator to make attitude or speed changes on the approach. So what technique do you actually use if say in this case you gain some GS on short final ?? Dont touch the power??? or use elevators??? and by making no power adjustments you will probably gain speed again until you establish the GP again and take up a constant descent rate???
Hope you can help me out of my confusion here!
Thanks
Fart