What procedure is employed to keep deicer boots flat against the airfoil surface during flight?

Applying suction to the boots is the correct procedure to keep deicer boots flat against the airfoil surface during flight. This method ensures that the boots adhere closely to the wing’s surface, minimizing aerodynamic drag and maintaining optimal airflow over the airfoil. The suction allows the boots to be held flat against the wing when they are not inflated, which enhances their functionality by promoting a smooth surface that is crucial for efficient aerodynamics.

When the boots are inflated with air to remove ice, they need to land back flat against the surface as they deflate. Suction effectively helps in this process, preventing any gaps that could negatively impact the aircraft's performance. The other choices, such as using adhesive materials or maintaining a constant temperature, do not adequately address the need for boots to conform tightly to the airfoil at all times as suction does. Moreover, while applying pressure from above could theoretically keep the boots in place, it is not a standard or effective method compared to suction, which is specifically designed for that purpose.