When does an aircraft begin to produce wingtip vortices?

An aircraft begins to produce wingtip vortices during the phase known as rotation, which occurs when the aircraft's main wheels leave the ground during takeoff. This is when the wings generate lift and a pressure difference forms between the upper and lower surfaces of the wings.

As the airflow over the wings creates lift, the higher pressure air from beneath the wings moves around the wingtips to the lower pressure above, resulting in swirling patterns of air known as vortices. These wingtip vortices are particularly strong and can contribute significantly to wake turbulence, which poses risks to following aircraft, especially smaller ones.

In the context of the other scenarios, only during rotation does the necessary lift generation occur to produce these vortices, while the other phases, such as landing and descent, either involve different aerodynamic conditions or reduced lift being generated. Thus, recognizing the key moment of rotation helps understand the onset of vortex generation during flight.