Height Above Airport (HAA) refers to the altitude of an aircraft or object above the elevation of a specific airport's reference point, typically the airport's runway threshold or a designated reference datum.

HAA is used as a reference to measure the height of an aircraft or object above the airport's surface, rather than above sea level (which is typically used for altitude measurements). This is important for pilots and air traffic controllers to understand, as it helps them to determine the aircraft's position and altitude relative to the airport's terrain and obstacles.

For example, if an aircraft is flying at an altitude of 1,000 feet HAA, it means that the aircraft is 1,000 feet above the elevation of the airport's reference point. This information is critical for safe navigation, especially during takeoff and landing phases, as it helps pilots to avoid obstacles and ensure a safe and stable approach to the runway.

It's worth noting that HAA is similar to other altitude measurements, such as "Height Above Ground Level" (HAGL) or "Above Ground Level" (AGL), which also measure an aircraft's altitude above a specific reference point. However, HAA is specifically related to the airport's elevation and is used to provide a more precise reference for pilots and air traffic controllers.