In what situation are vortices at their strongest?

Vortices are strongest on final approach primarily because of the configuration and behavior of aircraft during this phase of flight. When an aircraft is approaching to land, it is typically flying at lower altitudes and at lower speeds, producing significant wake turbulence. This turbulence is generated by the lift that the aircraft creates, particularly when large aircraft, with their significant wingspans, are near the ground, where the vortices do not dissipate as quickly as they do at higher altitudes.

During final approach, the aircraft's speed, proximity to the ground, and reduced maneuverability contribute to the strength and persistence of the wake vortex. These factors combined mean that any aircraft following the one that has just landed must be aware of and manage the risk of encountering these vortices, which can pose a serious hazard if not respected. The situation is heightened because the wake turbulence can linger in the landing area, and other aircraft may not be at a safe distance to encounter these vortices safely.

In contrast, during cases such as descending flight, climbing, or flying at high altitude, the vortices are either dissipating more rapidly or the aircraft are configured differently (e.g., altitude and speed) such that the impact of wake turbulence is reduced.