What is a secondary consequence of using lift or drag flaps during approach?

Using lift or drag flaps during an approach primarily modifies the airflow characteristics around the wings and the overall aerodynamic properties of the aircraft. One significant secondary consequence of deploying these flaps is the increase in stall speeds.

When flaps are deployed, they alter the wing's profile and increase the camber, which enhances lift at lower speeds. However, this modification can also lead to a higher stall speed than the clean (flap retracted) configuration. The reason for this increase in stall speed lies in the fact that while the flaps generate more lift at a given airspeed, they also change the critical angle of attack, which means that the safe operating speed margin becomes narrower. Consequently, pilots must be aware that flying close to this increased stall speed can risk inadvertently reaching critical angles without proper speed management, especially during high drag configurations like landing.

The other choices pertain to effects that are not accurate or relevant in this context. For instance, flaps do not typically decrease lift; rather, they enhance it during low-speed flight operations. Similarly, flap deployment does not enhance thrust or improve glide ratios; instead, it affects drag and lift characteristics, which are essential for safe landings.