What will happen to the true altitude when temperature decreases?

When temperature decreases, the true altitude will be lower than the indicated altitude. This phenomenon occurs because the altimeter in an aircraft is calibrated based on the standard atmosphere, which assumes a specific temperature at a given altitude. When the actual temperature is lower than the standard temperature, the air density is higher, resulting in the aircraft being at a lower altitude than what the altimeter indicates.

As the temperature drops, the density of the air increases, leading to a discrepancy between the indicated altitude and the true altitude. Pilots must consider this when interpreting altimeter readings, especially in colder conditions, as it can affect altitude awareness, safety, and navigation.

If the temperature were to remain constant or increase, the relationship between indicated and true altitude would differ significantly, but in the context of a decreasing temperature, the true altitude is indeed below what the altimeter indicates. Understanding this relationship is crucial for accurate altitude assessment in aviation.