What limitations apply to engine anti-ice usage on the ground?

When considering the operational limits for engine anti-ice usage while on the ground, the requirement is focused on atmospheric conditions that can lead to icing. Specifically, the guideline stipulates that anti-ice systems should be activated when the Outside Air Temperature (OAT) is 10°C or below, and there is visible moisture present. This is because at this temperature range, the likelihood of ice forming on the engine in the presence of moisture (such as from rain, snow, or high humidity) increases, which can significantly affect engine performance and safety.

Activating the anti-ice system under these conditions is crucial as it helps prevent ice from accumulating, ensuring that the engine operates efficiently. Flying or even taxiing in such conditions without activating the anti-ice measures could lead to ice buildup, potentially causing hazards like engine stall or performance degradation.

The other conditions related to temperature or moisture do not correctly encapsulate the necessary guidelines for safe engine operation regarding anti-ice usage on the ground. Therefore, recognizing the correct operational limit ensures adherence to safety protocols and effective aircraft performance in potentially hazardous environments.