When is the worst kind of wake turbulence encountered behind a heavy aircraft?

• A. On the ground
• B. When engines are running
• C. Clean and slow
• D. When the flaps are down

Answer: (C)

Wake turbulence from a heavy aircraft is strongest when the aircraft is carrying a lot of weight, in a clean configuration (flaps up, gear up), and flying slowly. The lift the wings must produce is large for a heavy airplane, and flying slowly requires a higher angle of attack to generate that lift. This combination creates the most powerful wingtip vortices, which linger longer and pose the greatest hazard to following traffic. The other scenarios don’t produce that same potent vortex pattern: on the ground there isn’t the same wing-generated wake, engine thrust alone doesn’t create the wingtip wake in the same way, and deploying flaps (down) changes the lift and wake characteristics in a way that isn’t the worst-case for wake turbulence.