What icing conditions require anti-ice actions and how are they implemented on a narrowbody?

• A. Visible moisture or icing conditions; wing anti-ice and engine anti-ice activated as indicated by weather and sensor data.
• B. Only dry air; no action.
• C. Icing conditions always require de-icing on both wings but never anti-ice.
• D. Anti-ice activates automatically in any flight.

Answer: (A)

Icing in flight is prevented with anti-ice protection when the air is in or expected to be in icing conditions, so ice doesn’t form on critical surfaces. On a narrowbody, this typically means using both wing leading-edge anti-ice and engine anti-ice. The wing anti-ice heats the leading edge to keep it above freezing, while the engine anti-ice protects the engine inlets and related components from ice buildup. Pilots assess conditions using weather data, ice detectors, and sensor readings that indicate icing or freezing temperatures, then engage the anti-ice systems with the appropriate switches. In many airplanes the anti-ice can be commanded automatically by the aircraft’s logic if icing is detected, but it’s not guaranteed to be on in every flight; crew monitoring and activation based on conditions are part of normal operation.

This differs from de-icing, which is about removing ice that has already formed, and from operating in dry air where no anti-ice action is required.