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:

Pilots must accurately determine the freezing level during preflight to assess airframe icing risk, as it occurs when flying in visible moisture at or below 0 degrees Celsius.
Relying on the standard lapse rate (2°C per 1,000 ft) to estimate the freezing level is unreliable and potentially dangerous, as actual atmospheric lapse rates vary significantly.
Atmospheric conditions like temperature inversions, often associated with warm fronts, can cause the actual freezing level to be drastically different (e.g., much higher) than what the standard lapse rate would suggest.
For accurate freezing level information, pilots should utilize official aviation weather resources such as Aviation Weather Center forecasts (including automated and G-AIRMETs) or vertical route profiles found in advanced weather applications.

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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.