Definition
The height of the Decision Altitude (DA) or Minimum Descent Altitude (MDA) above the highest runway elevation in the touchdown zone (the first 3,000 feet of the landing runway). HAT is published on instrument approach charts for straight-in approaches and is expressed in feet.
Plain English
How high you are above the runway when you reach the lowest altitude the approach lets you fly. It tells you, in feet, how far above the runway surface that minimum is.
Context Anchor
Seen on instrument approach charts, usually in the minimums section for a runway approach.
Why Pilots Care
Sets the exact altitude at which the pilot must decide to land or go around when flying an instrument approach in low visibility.
Grounding Statement
If the touchdown zone elevation is 600 feet and the approach minimum is 900 feet on the altimeter, the HAT is 300 feet.
Intuition Check
HAT is not the airplane’s actual height when the wheels touch down. It is the charted height of an approach minimum above the runway’s touchdown-zone elevation.
Example Sentence 1
The ILS minimums show a DA of 1,492 feet with a HAT of 200, so we'll need to see the runway environment by 200 feet above the touchdown zone.
Example Sentence 2
The pilot reached the HAT and immediately saw the runway lights.