FAA Ground School Practice Test

True altitude refers to the vertical distance of an aircraft above sea level. This measurement is crucial for navigation and safety because it provides pilots with an accurate understanding of their actual elevation relative to mean sea level (MSL), which is a standardized reference point.

True altitude is essential in various contexts, such as when flying in mountainous areas where terrain elevations can change rapidly, and knowing the precise altitude relative to sea level helps avoid obstacles. Additionally, it plays a significant role in maintaining safe vertical separation between aircraft during flight operations.

While the other options touch on different aspects of altitude or measurement, they do not accurately define true altitude. For example, setting the barometric pressure scale to 29.92 inches of mercury relates to pressure altitude, which is a different concept associated with atmospheric pressure rather than direct elevation above sea level. Similarly, the vertical distance of an aircraft above the surface refers to height, not true altitude, and the altitude indicated on water level would not provide the necessary reference to mean sea level critical for true altitude understanding.