When is cowl anti-ice required for takeoff?

Cowl anti-ice is specifically required for takeoff when there is visible moisture and the outside air temperature (OAT) is 10°C or below. This requirement is based on the fact that visible moisture can lead to ice accumulation on the engine cowl and other critical surfaces, which can negatively impact engine performance during takeoff. When the temperature is at or below 10°C, this condition increases the risk of ice forming, necessitating the use of cowl anti-ice systems to ensure safety and optimal engine operation.

The other options do not accurately reflect the specific conditions under which cowl anti-ice is mandated. For example, having ice already present or simply being below freezing does not account for the important factor of visible moisture, which is crucial for determining when cowl anti-ice should be engaged.