The amount of de-icing fluid required will be indicated by what sign?

The correct answer revolves around the importance of observing the behavior of the de-icing fluid during application. When de-icing fluid begins to drip off the leading and trailing edges of the aircraft, it indicates that the fluid has effectively melted the ice and has reached the point of being fully effective. This dripping shows that the ice is being cleared from critical surfaces, ensuring proper airflow and performance during takeoff.

This visual cue is crucial for pilots and ground crew as it helps them assess that the de-icing process is working as intended. It ensures that the aircraft is adequately prepared for safe operation in icy conditions. Other signs, such as evaporation or misting, do not provide the same clear indication of effectiveness as the dripping flow does.