When must the wing anti-ice system be turned on?

The wing anti-ice system must be activated when the outside air temperature (OAT) is 5°C or below and there is moisture present. This requirement is based on the need to prevent ice formation on the wings, which can adversely affect aircraft performance and safety. Ice can form on aircraft surfaces in conditions where temperature is at or near freezing and moisture is available, even if the temperature is above 0°C.

In the specified conditions of 5°C or below combined with moisture, the risk of ice accumulation increases significantly, making it crucial for pilots to engage the wing anti-ice system before such conditions can impact flight safety. This ensures that ice does not form on the wings and other critical surfaces, allowing for better aerodynamic performance during flight and landing.

In contrast, other temperature thresholds without the moisture criterion do not adequately address the potential for ice formation and thus do not provide the necessary safety measures required under those conditions.