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 runway). HAT is published on instrument approach charts for straight-in approaches and is expressed in feet.
Plain English
How high above the runway you are when you reach the lowest altitude an instrument approach lets you fly to. If the chart shows a HAT of 200, you are 200 feet above the runway at that point.
Context Anchor
Seen on instrument approach charts and in operations specifications when straight-in landing minimums are listed.
Derivation
The letters come from height above touchdown. In this term, touchdown means the runway touchdown zone used as the height reference, not the exact spot where the airplane’s wheels will touch down.
Why Pilots Care
HAT provides the exact height reference needed to decide whether to continue the landing or execute a missed approach, directly affecting safety and regulatory compliance.
Intuition Check
HAT is not an altitude above sea level. It is a published height above the runway touchdown zone reference for that approach.
Example Sentence 1
The ILS approach showed a DA of 1,250 feet with a HAT of 200, so we briefed that we'd need to see the runway environment by 200 feet above touchdown.
Example Sentence 2
The pilot checked the HAT value during the approach briefing to confirm the correct height for the landing decision.