# Why are the height values different although the altitude values in the "straight-in approach" and "circling" minimums are the same?

Why are the height values different although the altitude values in the "straight-in approach" and "circling" minimums are the same? For Adana airport, the minimum altitudes of the 05 runway VOR Z approach are the same (1200) but the heights are different (1148-1137). What is the reason for this? Is it due to the elevation of the region where the minimums are located? So where is the "circling" minimum accepted? The name of the chart document in Turkey AIP for LTAF airport is "AD 2 LTAF IAC - 2".

Straight-in is referenced to a particular runway, while circling is referenced to the airport elevation. The same elevation MSL is thus a different height above the referenced elevation.

The "runway elevation" for a particular runway is generally defined either as the highest point in the touchdown zone for that runway, or the elevation of the threshold. Thus the runway elevation can differ at opposite ends of the same physical runway. And the airport elevation, being the highest of these (or perhaps the highest landable surface - if a runway slopes down from the center in both directions), will often differ from several of the runway elevations on that airfield.

The salient point, though, isn't in the specific definition of each concept, but in the fact that a straight-in approach is referenced to its runway, while a circling approach, being not-runway-specific, is referenced to the airport.

• Those are of course accurate statements, but the question is conceptual: how can these 2 values be different? To which the answer is, they're different because they're referenced to two different things. How those 2 different values are generated is a little beside the point. What matters is, there are two of them, and they're often different.
– Ralph J
Commented Sep 1, 2023 at 15:58
• Thank you for your answer! But by the way, I didn't quite understand the comment of @RTO. What do you mean with this part: "for straight-in minimums the AGL altitude is measured above the highest runway elevation in the touchdown zone - HAT". Commented Sep 1, 2023 at 17:12
• Rwy 05 threshold altitude is 52 feet and rwy 23 threshold altitude is 63 feet at Adana airport. Since the altitude of the highest usable landing area is 63 feet, the airport elevation is also considered to be 63 feet. Commented Sep 1, 2023 at 17:14
• @pilot162 - your comment above explains it. I used the term HAT (AGL not MSL -height above touchdown - U.S. Terps). I believe for ICAO it would be the (AGL, not MSL) height above the threshold (not touchdown zone). So, I've deleted that comment for clarity.
– user22445
Commented Sep 1, 2023 at 17:27
• FWIW, I am in agreement with @RTO's since deleted suggestion. (The OP's query in comments backs the point.) I'm all for brevity and not over-answering, but I don't understand why there might be resistance to a very minor edit to add a few standard phrases for completeness that would make a good answer even better... Commented Sep 1, 2023 at 17:32