Try a simple test. Get on a bicycle and ride it with a 10 mph wind at your back. You will notice at a certain speed you will feel no wind in your face. That is what happens with an airplane there is a point where there is not enough wind flowing over the wings to generate lift. It usually happens when you are flying at or near stall speed and the tail wind suddenly climbs. There was a major airline crash in Dallas years ago where they determined that contributed to it I think.