What does the clean aircraft concept prohibit during takeoff?

The clean aircraft concept is a safety standard designed to ensure that aircraft are completely free of contaminants such as frost, ice, snow, or slush on critical surfaces during takeoff. This is crucial because these substances can significantly affect the aerodynamic performance of the aircraft, leading to reduced lift, increased drag, or overall handling difficulties. By prohibiting any contamination, the concept aims to ensure that the aircraft can achieve optimal performance during critical phases of flight, particularly takeoff when the aircraft needs to reach a specific speed and attitude safely.

The other options relate to different aspects of flight safety and aircraft operation, but they do not specifically pertain to the clean aircraft concept, which is singularly focused on ensuring that critical surfaces – like the wings and tail – are clear of any winter weather-related contaminants.