When flying over mountainous terrain in low temperatures, what should pilots be cautious of regarding altitude readings?

When flying over mountainous terrain in low temperatures, it is essential for pilots to understand the relationship between temperature and altitude readings due to the physics of how altimeters function. The correct choice indicates that the indicated altitude will be higher than the true altitude in cold temperatures, specifically in mountainous environments.

This phenomenon occurs because altimeters are calibrated based on the standard atmospheric conditions, which assume a certain temperature gradient in the atmosphere. When the air temperature is low, the density of the air is higher than what the altimeter is set to expect. As a result, the altimeter will read an altitude that is inflated when compared to the actual altitude—essentially making it seem as though the aircraft is at a higher altitude than it truly is.

This misinterpretation can become particularly critical when flying in mountainous terrain, where an incorrect altitude reading can lead to flying too low relative to the true terrain elevation, potentially resulting in controlled flight into terrain (CFIT) incidents. Understanding this critical factor helps pilots make better altitude assessments and maintain safer flying practices in challenging conditions.