Definition
A published instrument approach minimum that places the decision altitude or minimum descent altitude 200 feet above the elevation of the touchdown zone. On Copter-only approaches, a 200-foot HAT is the lowest standard height at which the pilot must have the required visual references in sight to continue the approach to landing.
Plain English
The lowest point you can descend to on this approach is 200 feet above the spot where you intend to touch down. If you can't see the landing area by then, you have to go around.
Context Anchor
Seen on helicopter instrument approach procedures, especially copter-only approaches to airports or heliports.
Derivation
HAT stands for Height Above Touchdown. The number 200 is simply the height in feet. The term is built from its parts, but the key idea is that the reference point is the touchdown zone elevation -- not sea level, not the airport elevation, and not the ground directly below the aircraft.
Why Pilots Care
It provides helicopter pilots with lower landing minimums than standard airplane procedures, increasing access to more landing sites in marginal weather.
Grounding Statement
Picture the landing surface as zero for that approach: 200-foot HAT means the published limit is 200 feet above that surface.
Intuition Check
Do not read 200-foot HAT as a height to maintain for the whole approach. It is the height of a published approach minimum above the touchdown elevation.
Example Sentence 1
The Copter ILS shows a 200-foot HAT, so we'll plan to go missed if the heliport isn't in sight by 200 feet above touchdown elevation.
Example Sentence 2
Once the heliport lights became visible at 200-foot HAT, the pilot continued visually to the landing pad.