Remember, that windshear (in the negative sense, i.e. suddenly reduced airspeed) is almost always a sudden, once off encounter. It is very rare and highly unlikely that you would suffer a severe shear which reduces your airspeed from say 160 knots to 140 knots and then have that followed a few seconds later by another drop from 140 knots to 120 knots.
I wouldn't be quite so sure about that... I remember doing a windshear exercise in the sim using a *real* recorded windshear event: There were two or three really nasty bits of shear, as well as considerable rolling moments. From start to finish, the loss of airspeed was >100kts as you went from flying into the outflow from a chain of microbursts to having the outflow behind you. Very sobering.
We has another go, letting the A/P fly it (very impressive) and with the sim set CAVOK, so you could see the ground/buildings/trees rushing past...
This has made me even more determined to *avoid* the stuff at any cost rather than fly through it.
I've had numerous 'discusions' in the flight deck about the sensible option (airmanship) of carrying considerable speed to the threshold - most a/c types ops manuals allow max 20Kts on Vref which is in itself a reasonable buffer against some of the severe windshear .....
.. I'd rather float and land long down a 3500m runway than risk dropping out the sky on finals!
Reference my previous paragraph, 'severe windshear' is something you really shouldn't be exposing your aircraft to, IMHO.
I think the term 'windshear' is used when often people really mean 'wind gradient' or 'low-level turbulence'. I would contend that you don't want a very large addition to your airspeed over the threshold, you want it further back in the approach, bleeding gradually off to touchdown. I think the FBW Airbuses have this protection? (GS min?). There are many more incidences of aircraft going off the end of runways than there are of them burying themselves in the approach lighting (AF at YYZ, SWA at Chicago etc.)
Looking at it from a practical POV: If it's gusty on the approach, say 30G50 with lulls to 15kts, the maximum loss of airspeed will be 35kts. For an aircraft with a nominal Vref of 120kts @1.3Vs using Vref+10 = 130kts, you have a margin of 38kts. This is the worst possible case for a *momentary* reduction in airspeed. You also have the engines available to counteract this loss, so the chances of actually stalling the aircraft are very slim. If you land deep into a wet runway at Vref+25 the 'plane will go quite a way before you come to a halt, maybe beyond the end... I'm not a great believer in extra airspeed "for Mum" as I think you are just trading one thing for something else, potentially just as dangerous. If it's really that bad: go somewhere else.
