Comment by ryandrake

Airplanes are always traveling forward relative to the wind, at some angle of attack. Tailwinds don't work by blowing against the airplane's surface and pushing it forward. Since the airplanes are themselves traveling at, say, N kt forward relative to the wind, then if they are inside a 10 kt tailwind, they'll be doing N+10 kt over the ground, if they are inside a 50 kt tailwind, they'll be doing N+50 kt over the ground. If they are inside a 25 kt headwind, the'll be doing N-25 kt over the ground.