Keep it simple, guys! Of course it has nothing to do with your ground speed. It's the air speed that keeps you in the air, be it true or indicated or whatever...the motion of the aircraft in regards to the surrounding air. Now, I'm pretty shocked to see so many explanations from experienced people not being close to the truth. Try this in a simulator: W/V: 360/100kts. HDG:360. IAS: 100kts. This will give you GS:0kts. Then simply change the heading to 180, as you would in a turn, except that this happens instantly, not letting the aircraft accelerate. Of course it will fall out of the sky, because of negative airspeed.
How about it, Avi8tor? I hope at least you'll agree...
