How is true altitude defined?

True altitude is defined as the altitude above sea level. This measurement provides a crucial reference point for aircraft altitude and is determined relative to the mean sea level (MSL). Understanding this concept is essential for pilots, as true altitude is vital for ensuring safe flight operations, requiring knowledge of terrain elevation and air traffic regulations.

When a pilot refers to altitude in navigation and communication, they typically mean true altitude, as this standard measurement allows for consistency in understanding an aircraft's position in the airspace relative to the Earth's surface. Factors like atmospheric pressure and the curvature of the Earth can affect other altitude measurements, but true altitude remains constant because it is always referenced directly from sea level.