Touchdown Zone Elevation (TDZE)
Touchdown Zone Elevation (TDZE) is the highest elevation in the first 3,000 ft of the landing surface of the runway. It is the elevation datum used for computing Height Above Touchdown Zone (HAT) — the height component of instrument approach minimums.
TDZE vs. Airport Elevation
Airport elevation is the highest point on the entire aerodrome. TDZE is the highest elevation within the first 3,000 ft of the specific runway end. These may differ on runways with slopes or at complex airports. Approach minimums use HAT (height above TDZE) to ensure terrain clearance is meaningful relative to where the aircraft actually touches down.