What is the relationship between pressure altitude and true altitude?

The correct choice highlights that pressure altitude is defined based on standard atmospheric conditions, specifically the assumption of a standard atmosphere model. Pressure altitude is the height at which the atmospheric pressure is equal to 29.92 inches of mercury (inHg) or 1013.25 hPa, which corresponds to the standard atmospheric pressure at sea level. This measure allows pilots and air traffic control to ensure consistent altitude reporting across different aircraft, regardless of local variations in atmospheric pressure.

In contrast, true altitude is the actual height of an object above sea level, which can vary due to local atmospheric conditions, such as temperature and air pressure variations. As a result, while pressure altitude and true altitude can sometimes be the same (for instance, under standard conditions), they are not equivalent at all times due to these variable atmospheric influences. Understanding this relationship is crucial for accurate altitude measurements, navigation, and safety in aviation.