When will pressure altitude equal true altitude?

Pressure altitude will equal true altitude when standard atmospheric conditions exist. Standard atmospheric conditions are defined as a temperature of 15 degrees Celsius at sea level and a pressure of 29.92 inches of mercury (Hg). Under these conditions, the atmospheric pressure and the altitude calculations align perfectly, allowing for a direct correlation between pressure altitude (the height above the standard datum plane) and true altitude (the actual height above mean sea level).

When standard conditions are not present, variations in temperature and pressure can lead to discrepancies between pressure altitude and true altitude. For example, if the temperature is higher or lower than the standard, the true altitude will differ from the pressure altitude, as the density of the air directly influences altimeter readings. Recognizing this relationship is essential for accurate altitude awareness during flight.