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

Verified

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

Key Takeaways:

The standard lapse rate method (2°C/1,000 ft) is an unreliable and potentially dangerous way to estimate freezing levels for aviation icing risk due to variable atmospheric conditions like temperature inversions and enhanced lapse rates in the planetary boundary layer.
Using the standard lapse rate can lead to significant errors, either causing pilots to believe the freezing level is higher than it is (underestimating risk) or lower than it is (overestimating risk and potentially missing safe altitudes).
For accurate assessment of airframe icing potential, pilots must rely on official meteorological data sources such as the Aviation Weather Center's freezing level forecasts, G-AIRMETs, Skew-T diagrams, or vertical route profiles in aviation weather applications.

See a mistake? Contact us.

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.