True altitude is defined as what?

True altitude refers to the actual vertical distance of the aircraft above sea level. It is an important measurement in aviation since it helps pilots understand their position relative to geographic features and navigational aids. True altitude is particularly vital when flying in mountainous terrain or planning routes that involve specific vertical clearances.

When pilots refer to true altitude, it ensures that they are operating the aircraft at the correct height above a consistent reference point—the mean sea level—rather than a different reference, such as the ground at a specific location, which could vary widely. This distinction is crucial for maintaining safe vertical separation from terrain and obstacles, especially given that air pressure and temperature can vary significantly, impacting altitude readings from altimeters. By using true altitude, pilots can effectively manage their altitude and ensure safety during flight.

Other definitions, such as the altitude indicated by the GPS system or the vertical distance above the aircraft's base, do not provide a reliable standard for height above sea level and can lead to misunderstandings or navigation errors in flight planning and execution.