What typical external condition can cause an altimeter error during flight?

Temperature variations from the standard atmosphere can lead to altimeter errors during flight primarily due to the relationship between temperature and atmospheric pressure. Altimeters are calibrated to the standard atmospheric model, which assumes a specific temperature profile. When the actual temperature deviates from this standard, the air density changes, causing the altimeter to read inaccurately.

For example, if the air temperature is warmer than standard, the actual pressure at a given altitude is lower than what the altimeter is set for, which would make the altimeter read higher than the aircraft's true altitude. Conversely, if the air is colder than standard, the altimeter would read lower than the actual altitude. This discrepancy is significant for pilots because it affects altitude awareness and can be critical during approaches and landings. Thus, understanding how temperature affects the altimeter is essential for maintaining accurate altitude control.