Which icing conditions require anti-ice/de-ice systems and what are common indicators of icing?

• A. Visible moisture near freezing; indicators include ice accumulation on surfaces, frost, and reduced performance
• B. Any moisture regardless of temperature
• C. Only in freezing rain
• D. Only during high humidity at warm temps

Answer: (A)

Ice forms on aircraft surfaces when there is visible moisture in the air and the temperature is near freezing. In that window, droplets can strike the airplane, freeze on contact, and rapidly build up ice on wings, tail surfaces, and other exposed areas. Because ice changes the airfoil shape, it adds weight, increases drag, dulls lift, and can alter handling, which is why anti-ice and de-ice systems are used in these conditions to prevent or remove ice.

Indicators you’re encountering icing include ice accumulation on surfaces, frost forming on wings or other parts, and a noticeable drop in performance or changes in handling—such as reduced climb or acceleration, higher stall speed, or unusual control feel. The other options don’t fit because icing isn’t guaranteed with any moisture at all temperatures, isn’t limited to freezing rain, and doesn’t require warm, high-humidity air to occur.