Staying on Top of the Freezing Level

Winter and airframe icing are like peanut butter and jelly; it’s hard to imagine one without the other.

Monday, April 10, 2023 at 09:46 AM ET

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Winter and airframe icing are like peanut butter and jelly; it’s hard to imagine one without the other. [Credit: iStock]

Key Takeaways:

Using the standard lapse rate (2°C/1,000 ft) to estimate the freezing level is unreliable and potentially dangerous, as actual atmospheric conditions, like higher lapse rates in the boundary layer or temperature inversions, often deviate significantly.
Incorrectly calculating the freezing level can lead to pilots encountering unexpected airframe icing at lower altitudes or misinterpreting accident causes, highlighting the critical need for accurate preflight analysis.
Pilots should rely on official meteorological products for accurate freezing level forecasts, such as the Aviation Weather Center's hourly lowest freezing level charts, G-AIRMETs, Skew-T log (p) diagrams, or vertical route profiles found in aviation weather apps.

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Short of an erroneous forecast or calibration issue with your immersion thermometer, if you can remain below the lowest freezing level during your entire flight, there’s typically no chance for an encounter with airframe ice. Induction ice is certainly possible, but not airframe ice.

If you plan an altitude where the temperature aloft is zero degrees Celsius or less, airframe icing becomes exceedingly more likely while flying in visible moisture. Therefore, the freezing level is one key variable that you need to determine during your preflight analysis to better quantify your risk of airframe ice.