What must pilots do before they can takeoff if they suspect frost on their aircraft?

Ensuring that there is no frost on critical surfaces is essential before takeoff because frost can significantly impact an aircraft's aerodynamics and performance. Frost can disrupt the smooth airflow over wings and control surfaces, leading to increased stall speed, reduced lift, and difficulty in controlling the aircraft during takeoff and initial climb. Critical surfaces include areas like wings, tailplanes, and control surfaces where the smooth flow of air is crucial for optimal performance.

While using heat to remove frost is a valid method and may be necessary depending on the situation, it does not guarantee that all frost has been completely removed from critical surfaces unless it is checked visually following the application of heat. Waiting for the sun to melt the frost can be unpredictable and may not sufficiently address frost that has formed on shaded parts of the aircraft. Filing a weather brief, although important for a thorough understanding of current conditions, does not directly address the immediate issue of frost on the aircraft. Therefore, checking that there is no frost on critical surfaces is the primary action required to ensure safety before flight.