Foxmoth - of course you're right, I am guilty of not explaining myself properly - the extra bit (that you do have to consider the inertia of the aeroplane) does nevertheless cause confusion at first. This is because the temporary change in airspeed can only be understood by referring to the speed of the aircraft in a frame of reference outside of the air - and that frame of reference is the earth, in other words ground speed. By frame of reference I mean that speed has to be expressed as movement between two things. Airspeed is the movement between the aircraft and the parcel of air it is in. When we talk about wind gradient we are using the earth as the fixed frame of reference (ie the speed between the air and the ground)and we have to use the same frame of reference for the aircraft when we want to describe what happens as the aircraft descends through the wind gradient. This does not mean that the aeroplane somehow magically knows what it is doing with respect to the ground - but we need the ground to anchor our mental description of what is going on. Hence the confusion.
This is what happens when you teach a PhD physicist to learn to fly and he unpicks your explanations...
Last edited by Heston; 14th Jan 2014 at 21:35.