Under what conditions is anti-ice needed when taxiing?

The need for anti-ice when taxiing is primarily determined by both the temperature and the presence of moisture or contamination on the ground. When options indicate conditions such as ground contamination or visible moisture combined with an outside air temperature (OAT) of 10°C or below, it highlights a scenario where ice can form on critical surfaces of the aircraft.

When the temperature is at or below freezing and there is moisture (like rain, snow, or ice) present, there's a high risk of ice adhering to the wings and other surfaces, which can significantly affect aircraft performance. Therefore, activating anti-ice systems in these conditions is essential to ensure the aircraft is clear of ice before takeoff.

In contrast, other scenarios such as having an OAT above 10°C typically do not warrant anti-ice measures because the risks of ice formation are considerably lower. Similarly, conditions involving rain alone without the additional element of freezing temperatures and moisture do not inherently require anti-ice because the ambient temperature may prevent ice from forming. Thus, the specific combination of freezing temperatures with moisture or contamination makes the need for anti-ice critical.