When the temperature is lower than ISA an aircraft will be lower than indicated by the barometric altimeter. Consequently, there is a risk that the specified clearance above obstacle is no longer sufficient and the effect of the low temperature must be compensated. The most efficient means to mitigate this effect is t quantify the effect of the difference from ISA in form of a correction that should be added to the minimum flight altitudes to ensure the appropriate clearance above obstacles and terrain. ATS Authorities are responsible to develop and establish the necessary corrections for the cold temperature effect on altimetry and provide the air traffic control the values for minimum flight altitudes/ minimum vectoring to be used in cold temperature conditions.
EUROCONTROL Guidelines for Cold Temperature Corrections by ATS
This document contains guidance for the ATS Authorities to develop and establish the necessary corrections for the cold temperature effect on altimetry, and a common set of methods to be used for providing the air traffic control with the minimum flight altitudes to be used when corrections for the cold temperature effect on altimetry are required.