What action can be taken to ensure braking efficiency during descent?

To ensure braking efficiency during descent, modulating the brake pressure gradually is the most effective action. This technique allows for a controlled application of braking force, which helps in managing the heat generated by the brakes and prevents them from overheating. By gradually increasing brake pressure, the pilot can maintain optimal braking performance without risking a sudden loss of control or excessive wear on the braking system.

Employing this gradual modulation technique also helps in adjusting braking to the specific conditions encountered during descent, such as varying aircraft weight, speed, and environmental factors like wind and runway surface conditions. This method promotes stable and predictable braking behavior, leading to safer and more efficient landings.

In contrast, the other options do not directly enhance braking efficiency during descent. For instance, reducing control surface effectiveness may compromise the aircraft's handling. Extending the flaps fully, while it can increase lift and drag, does not necessarily correlate with braking efficiency. Lastly, applying full power to the engines during descent would generally increase speed and prolong the descent rather than contribute to efficient braking. Thus, the most effective choice remains the gradual modulation of brake pressure.