I had a discussion about air speeds with one of my instructors recently. He is claiming that there is a sudden drop in the wind velocity as you get closer to the ground (which is absolutely true, due to the wind friction with the ground). However, he also says that this will affect the airspeed by making it lower and this could be dangerous because it could lead to stall conditions.
For example: he says that, if my approach is with 90km/h airspeed, the headwind is 30km/h at a certain height and by the ground the headwind goes down to 10km/h, and the stall speed is 80 km/h, I will stall because the air speed will drop down to 70km/h.
Here is where I am confused, since I have read before that the wind does not affect the air speed in any way and it will only affect the ground speed by making it 20km/h higher.
Could you please try to make this clear for me?