During which phase of flight do leading-edge flaps primarily improve performance?

Leading-edge flaps are primarily designed to enhance the aerodynamic properties of an aircraft during slower flight speeds, particularly when higher lift is required. During the landing approach phase, the aircraft operates at reduced airspeeds and generally requires increased lift to maintain level flight and control before touchdown.

By extending leading-edge flaps, the wing's camber is increased, which enables the aircraft to generate more lift at lower speeds. This is crucial when approaching to land, as it allows the pilot to safely manage the descent and touch down at an appropriate speed without stalling. The performance improvement provided by leading-edge flaps is less critical during climb out, descent, or cruise, where the aircraft is typically flying at higher speeds and may already have sufficient lift without additional drag from these devices.