How is true altitude defined?

True altitude is defined as the height of an object above mean sea level (MSL). This measurement provides a standard reference for aviation and meteorology, allowing pilots to understand their altitude in relation to the surface of the Earth and sea levels, which are critical for safe navigation and terrain avoidance. By using MSL as a baseline, true altitude ensures that pilots have a consistent frame of reference regardless of local topography, weather conditions, or fluctuations in atmospheric pressure.

This definition is particularly important for flight operations, as it enables pilots to operate at designated altitudes above the MSL, thereby ensuring they maintain safe vertical separation from obstacles and other aircraft. Knowing one's true altitude assists in flight planning and in adhering to regulatory requirements for altitude assignments in controlled airspace.