Vortices are generated at the moment the aircraft ____.

• A. begins engine run-up
• B. touches down
• C. leaves the ground
• D. lands

Answer: (C)

Wingtip vortices form when the wings generate lift by deflecting air downward. On the ground, the airplane’s weight is supported by the landing gear, so the wings aren’t producing significant lift and no strong vortices are shed. The moment you leave the ground, the wings begin to generate lift as you rotate and climb, creating the downward air flow and trailing vortices behind the airplane. Thrust during a run-up doesn’t create those vortices because it isn’t producing lift. During landing, lift is already present while you’re in the air, but the initial creation of vortices occurs when the aircraft leaves the ground.