When do the wing anti-ice valves close automatically?

The wing anti-ice valves are designed to enhance the safety and performance of the aircraft by preventing ice accumulation on the wings during flight. They play a crucial role in ensuring that the wings maintain their aerodynamic properties in icy conditions.

The correct scenario for when the wing anti-ice valves close automatically is upon touchdown. This safety feature is in place to prevent unintended operation of the wing anti-ice system while the aircraft is on the ground, allowing for a safe operation of the aircraft during landing and subsequent ground handling. It is essential that the anti-ice system is deactivated on the ground to conserve energy and to prevent any potential hazards from occurring.

In contrast, the other scenarios do not align with the operational protocols for the wing anti-ice system. For instance, automatic closure of the valves during the takeoff roll could lead to unexpected performance issues as ice formation is countered during this critical phase of flight. Similarly, closing the valves upon reaching cruise altitude does not effectively address the potential icing conditions that can occur during the flight. Lastly, closure upon engine shutdown, while it may seem plausible, is not the primary operation context for the anti-ice systems during flight operations.