Final answer:
The 'clean aircraft' policy in cold weather involves procedures to ensure that aircraft surfaces are free of ice and snow through de-icing and anti-icing methods, using chemicals that lower the freezing point of water, and includes regular maintenance programs.
Step-by-step explanation:
The policy for a "clean aircraft" in cold weather typically refers to procedures airlines and pilots must follow to ensure that aircraft are free of ice and snow build-up, which can compromise the aircraft's safety and performance. This involves the practice of de-icing and anti-icing. De-icing removes ice and snow from the aircraft's surfaces after they have formed, while anti-icing involves treating surfaces to prevent ice from forming. These measures are critical because ice accumulation can alter the shape of the aircraft's wings and control surfaces, adversely affecting aerodynamics and potentially leading to reduced lift and control issues.
Specific policies may include applying chemicals to aircraft surfaces that lower the freezing point of water, a process known as freezing point depression. These chemicals can be applied before flight to prevent ice from forming and during flight on surfaces equipped with de-icing systems. Regular maintenance programs are also essential to ensure the effectiveness of these measures and to avoid potential problems, such as the growth of biofilms in systems like the air conditioning unit, which can be a health hazard as well as affect the system's efficiency.