“All landings must be made directly into the wind, Dad,” Bill explained patiently. “A plane stalls when its speed through the air drops below a certain point. If there’s no wind its speed over the surface will be the same as its speed through the air. But any wind at once affects its velocity over the surface, which will be the composition of the speed of the plane through the air with the speed of the air over the surface. You see, a plane which stalls at forty miles an hour will, when landing into a fifteen-mile wind, make contact at twenty-five miles an hour. The same plane headed down-wind would land at fifty-five miles an hour. And that difference of thirty miles an hour in landing speed might easily spell the difference between a good landing and a wrecked plane.”