What is the general requirement for using anti-ice fluids?

The requirement for using anti-ice fluids is centered around ensuring the safety and performance of the aircraft before takeoff in conditions that could lead to ice contamination on critical surfaces, particularly the wings and control surfaces. When ice accumulates on these surfaces, it can disrupt airflow, severely affecting the aircraft's lift, drag, and overall performance.

By stating that all aircraft must apply anti-ice fluids before takeoff, the emphasis is on a proactive approach to eliminate any risk associated with icy conditions. This standard is rooted in the need for a consistent method to maintain aircraft safety and performance standards regardless of the specific ambient temperature, as even slight moisture in the air can lead to icing conditions when temperatures hover around freezing.

Other options may suggest conditional uses of anti-ice fluids, such as temperature thresholds, severe weather conditions, or takeoff from clear runways, which can lead to an inconsistency in safety practices and may not adequately address the inherent risks of ice on an aircraft. Thus, requiring all aircraft to use anti-ice fluids before takeoff ensures uniformity and a higher margin of safety.