When must windshield heat be activated?

Windshield heat should be activated below 30 degrees and during flight after takeoff to ensure clear visibility. This is particularly important because the moisture from the air can freeze on the windshield, obstructing the pilot's view and potentially leading to dangerous situations. Activating the windshield heat in these conditions helps to prevent frost or ice accumulation, maintaining safety during flight operations when temperatures are low.

While it may seem reasonable to activate windshield heat at any altitude when temperatures drop, it is specifically critical to do so below 30 degrees to effectively combat the freezing of moisture. The requirement is also not limited to just the landing phase, as visibility during all phases of flight is essential. Activating the heat when temperatures exceed 30 degrees would not be necessary, as the risk of ice or frost formation is not as prominent at these warmer temperatures. Thus, the correct answer emphasizes the specific conditions under which windshield heat is required for safe flight operations.