Height Above Touchdown Zone Elevation (HAT)

Height above touchdown zone elevation (HAT) is the height of the decision height (DH) or minimum descent altitude (MDA) above the elevation of the highest point within the touchdown zone of the runway used for the approach. HAT is the operationally meaningful height reference for a straight-in approach.

Why HAT Matters

The aerodrome elevation and the touchdown zone elevation may differ significantly at airports with sloped runways or multiple runways at different elevations. HAT ensures the approach minimums are expressed relative to the actual runway surface the aircraft is approaching, providing an accurate picture of terrain clearance at the critical decision point.

Related Terms

See also: HAA, Decision Height, MDA.