Which statement is true regarding vortex circulation in the wake turbulence generated by an aircraft?

The statement indicating that the vortex strength is greatest when the generating aircraft is heavy, clean, and slow is accurate. The strength of wake turbulence resulting from an aircraft is influenced by a variety of factors, including its weight, configuration, and speed. When an aircraft is heavy, it generates more lift, which results in stronger vortices. A clean configuration means the aircraft has less drag and turbulence, which also contributes to stronger and more well-defined vortices. At lower speeds, the circulation around the wings can become more pronounced, leading to increased vortex strength.

In contrast, factors such as reducing weight, altering the aircraft's configuration, such as deploying flaps or landing gear, or flying at higher speeds can lead to weaker vortices. This is why understanding the conditions under which vortices are generated is crucial for maintaining safe distances behind aircraft during takeoff, landing, and other phases of flight.