Floating caused by the phenomenon of ground effect will be most realized during an approach to land when at

• A. Less than the length of the wingspan above the surface
• B. The length of the wingspan above the surface
• C. Two wingspans above the surface
• D. Five wingspans above the surface

Answer: (A)

Ground effect is the cushion of air created when the wing is close to the surface, which reduces induced drag and effectively increases lift for a given airspeed. This effect is strongest when the airplane is within about one wingspan of the surface and fades as you climb away. During an approach to land, you’ll notice the airplane floating more as you get close to the ground because you’re still within that strong ground-effect zone. Once you are farther than roughly one wingspan above the surface, the ground effect diminishes and the floatiness decreases. Therefore, the most floating occurs when you are less than the wingspan above the surface.