Originally Posted by
Discorde
The add-ons are designed to counter horizontal windshear effects (wind strength decreasing as the ground is neared) and apply only to headwind component to counter loss of lift resulting from slow change to 'inertial' groundspeed.!
Thank you; that's certainly my interpretation, and though it could be interpreted either way, logically a perpendicular gust or ground effect variation in windspeed is not going to affect the IAS, so there shouldn't be an addition. (In practice, of course a couple of knots for mum, or more empirically, a knot or three for the sin of the crab angle, same thing. but ref+ 15, fluctuating+20 and you're in trouble on a short wet runway with no head component..