We all know that having the incorrect altimeter setting can have a devastating outcome if you are shooting an instrument approach. A small deviation in the Kollsman window can make a difference of a few hundred feet, which can mean the difference between life and death in some situations. In addition to the pressure we set in the Kollsman window, extremely cold temperatures can affect the altimeter setting, making flight unsafe unless you make adjustments.
The FAA recently issued a notam with relation to altimeter adjustments for 14 CFR Part 97 instrument approaches at 272 cold-temperature-restricted airports around the country. It was determined that beyond certain temperatures at these airports altimeter error would not ensure the required obstacle clearance (ROC). As a result, each airport has a set temperature beyond which pilots must adjust the altitude used and report the corrected altitude to ATC. These cold temperature restrictions ensure that the ROC can be maintained.
Unless you are flying an altitude compensating airplane, you need to calculate the altitude adjustment using a table published in AIM 7-2-3 called ICAO Cold Temperature Error Table. The table’s left column shows the temperature at the airport and the top row shows the altitude above the airport. You would use the altitude at the final approach fix and subtract the airport elevation to get the altitude to use for the top row. The intersection of the column and the row shows the amount of altitude adjustment to apply.
Here is a list of the Cold Temperature Restricted Airports.
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