What is the freezing level and why is it important for flight planning?

• A. The altitude where the air temperature is -10°C; used to determine cold-soak risk.
• B. The altitude where the air temperature is 0°C; crucial for icing risk assessments and anti-icing/defrost planning.
• C. The height where air pressure equals sea level; used for altimeter calibration.
• D. The altitude where the air becomes completely dry; used to predict fog

Answer: (B)

The freezing level is the altitude at which the air temperature is 0°C. This is a key reference for flight planning because icing risk is closely tied to temperature and moisture in clouds. Icing typically occurs when visible moisture is present in clouds at temperatures around 0°C to about -20°C, so knowing where the air first reaches 0°C helps you identify where icing could begin and how to plan anti-icing or defrost measures, or choose altitudes that minimize exposure. It’s common to use forecast freezing level heights on weather briefings to map safe routes and altitudes. The other choices describe different concepts (specific temperatures not tied to the standard freezing reference, sea-level pressure, or dry conditions) and do not reflect what the freezing level represents.