Definition
On a precision instrument approach, the specified point at which the pilot must decide whether to continue the approach to landing or execute a missed approach. Decision Altitude (DA) is expressed in feet above mean sea level (MSL) and read from the altimeter. Decision Height (DH) is expressed in feet above the runway threshold or touchdown zone elevation. At DA/DH, the pilot must have the required visual references for the runway in sight and be in a position to make a normal landing; if not, an immediate missed approach is required.
Plain English
The exact altitude on a precision approach where the pilot has to make a go/no-go call: if the runway is visible and the aircraft is positioned to land normally, continue; if not, go around immediately.
Context Anchor
Seen on instrument approach charts and used during the approach briefing before flying the final part of the approach.
Derivation
‘Decision’ comes from Latin decidere, meaning ‘to cut off’ — the pilot cuts off the descent at this point and commits to landing or going around. ‘Altitude’ is measured from sea level; ‘height’ is measured from the runway. The two terms exist because different altimeter references are used in different parts of the world.
Why Pilots Care
It is the last point at which a safe decision to land or go around can be made, directly affecting safety in low-visibility conditions.
Grounding Statement
Picture descending toward a runway in cloud: DA/DH is the point where “I see enough to land” or “I climb away now” must happen.
Intuition Check
Do not read “decision” as a flexible thinking period. The decision must be made at DA/DH. Also, altitude and height are not the same here: altitude is measured from mean sea level; height is measured from the runway threshold elevation.
Example Sentence 1
Approaching the Decision Altitude on the ILS, the pilot saw the approach lights clearly and continued to landing.
Example Sentence 2
At decision height the pilot saw the runway threshold lights and continued the landing.