The aircraft is flying in reference to the air, not the ground. Lets exadurate it a bit. for effect Say the plane is flying into a 100 mph headwind, and has a top speed of 100 mph so its standing still with an airspeed of 100 mph and ground speed of 0. it now turns downwind. Its airspeed is still 100 mph, and ground speed is now 200 mph. IF you were in the plane, you would not feel any acceleration because none takes place - relative to the air. Nor will it accelerate relative to the ground - it will appear to gain 100 mph during the turn at a rate proportional to its turn rate. IF the plane does 360 deg turns in this same 100 mph wind it will make a circle in reference to the air - and long button hooks to an observer on the ground. The wind does not cause any acceleration if it remains constant. The inertia reference is the atmosphere, not the ground. The only time the airspeed will change due to the wind is if the wind changes direction/speed. An increase in tailwind will accelerate the plane and at the same time reduce the airspeed. Aircraft can stall at any airspeed due to banking and loading factors.