In what circumstances is deicing or icing control equipment necessary?

Deicing or icing control equipment is necessary for flights in known or forecast icing conditions because ice accumulation on an aircraft can significantly impair its performance and safety. When flying through clouds or precipitation at temperatures around freezing, there's a risk of ice forming on critical surfaces such as wings, tail, and control surfaces, which can alter the aerodynamics of the aircraft and lead to issues such as loss of lift, increased drag, and even control difficulties.

Using deicing or anti-icing equipment helps prevent ice from forming or removes ice that has already formed, ensuring that the aircraft maintains safe operational capability. Although it can be cold enough for icing potential in temperatures below freezing, it is specifically the presence of known or expected icing conditions during a flight that necessitates the activation of this equipment. Night flights and pre-flight checks do not inherently require deicing measures unless they coincide with icing conditions. The focus on the forecast or known icing conditions is crucial for ensuring flight safety above all.