What is the problem with flying baro-VNAV in really cold weather?
A. Altimeters are susceptible to atmospheric-related error, and when the temperature is colder than standard, this error can become significant, with your altimeter reading higher than your actual altitude. Some charts list minimum temperatures for certain minimums, and the reason is that your actual altitude is below the altitude that would be displayed on your altimeter. Sometimes there are limitations associated with the availability of a local altimeter as well. The pilot is expected to account for this error in extremely cold conditions (as discussed in the AIM).
