Definition
A specified altitude or height in a precision approach or approach with vertical guidance at which a missed approach must be initiated if the required visual reference to continue the approach has not been established. Decision Altitude (DA) is referenced to mean sea level. Decision Height (DH) is referenced to the threshold elevation. The ICAO definition is used internationally and aligns closely with FAA usage, with DA/DH marking the go/no-go point on an approach with vertical guidance.
Plain English
On an approach where the aircraft is descending along a guided path toward the runway, this is the altitude or height at which the pilot must either see enough of the runway environment to land or immediately go around. DA is measured from sea level; DH is measured from the runway threshold.
Context Anchor
Seen on instrument approach charts, during approach briefings, and in procedures for approaches that provide vertical guidance.
Derivation
From Latin decidere, 'to cut off, determine.' The point where the descent must be cut off if the runway is not visually acquired. 'Altitude' is referenced to sea level; 'height' is referenced to the ground (in this case, the threshold). The pairing reflects two different reference systems used in different parts of the world.
Why Pilots Care
It marks the final commitment point for landing or going missed, preventing descent into terrain when visual contact is lost.
Analogy
It is like a final yes-or-no point on a road in fog. If you can clearly see where to go at that point, you continue; if not, you take the safe exit route.
Intuition Check
Do not read “decision” as a casual moment to think it over. In this term, the decision point is fixed by the procedure: at that altitude or height, continue only if the required visual reference is there; otherwise start the missed approach.
Example Sentence 1
Approaching the DA of 1,250 feet, the captain saw the approach lights and continued to land.
Example Sentence 2
At decision height the crew saw no runway lights and began the missed approach climb.