What is the safe action when encountering visible moisture in icing conditions?

Activating wing anti-ice is the correct action when visible moisture is encountered in icing conditions because this system is specifically designed to prevent ice accumulation on the wings. In situations where there's visible moisture—like during rain, snow, or mist—combined with temperatures at or below freezing, the aircraft is at a significant risk for ice formation. Ice can severely affect lift, control, and overall aircraft performance.

By turning on the wing anti-ice, the pilot ensures that the wings are adequately heated to prevent ice buildup, maintaining aerodynamic efficiency and safety during flight. This proactive measure helps in avoiding the potentially hazardous effects of icing.

Other options may not adequately address the threat posed by the conditions. Maintaining altitude or descending without activating ice protection might not prevent ice from forming. Increasing airspeed can provide some marginal benefits in certain scenarios but is not a substitute for activating the anti-ice systems, which are explicitly designed to handle icing conditions effectively.