Definition
The height of the Decision Altitude (DA) or Minimum Descent Altitude (MDA) above the elevation of the runway threshold, expressed in feet. HAT is published on instrument approach charts for straight-in approaches and tells the pilot how high they will be above the runway threshold when they reach minimums.
Plain English
How many feet you will be above the runway's landing end when you reach the lowest altitude the approach lets you fly to. It is a straight vertical measurement from the start of the runway up to your minimums.
Context Anchor
Seen on instrument approach charts in the landing minimums section for a specific runway.
Derivation
Threshold comes from an old word for the entrance to a doorway. In aviation, the runway threshold is the entrance to the landing runway, so HAT is measured above that runway entrance’s elevation.
Why Pilots Care
HAT tells the pilot the exact height at which to make the land-or-go-around decision during an instrument approach.
Grounding Statement
If the runway threshold is 500 feet above sea level and the published minimum altitude is 750 feet above sea level, the HAT is 250 feet.
Intuition Check
HAT is not height above sea level, and it is not always height above the airport field elevation. It is height above that runway’s threshold elevation.
Example Sentence 1
The approach plate showed a DA of 740 feet with a HAT of 250, so at minimums we would be 250 feet above the threshold.
Example Sentence 2
Approach minimums list both the MSL decision altitude and the equivalent HAT value.