Definition
On a precision or approach-with-vertical-guidance instrument approach, the specified altitude (DA, referenced to mean sea level) or height (DH, referenced to the runway threshold or touchdown zone) at which the pilot must decide whether to continue the approach to landing or execute a missed approach. The decision is made based on whether the required visual references for the runway environment are in sight at that point.
Plain English
It is the lowest point on the descent where the pilot has to look up and decide: if the runway or its lights are clearly in sight, continue and land; if not, go around and try again or divert.
Context Anchor
Seen in the profile view and minimums area of an instrument approach chart, especially on approaches that guide the airplane downward toward the runway.
Derivation
Decision altitude is given in feet above mean sea level (read off the altimeter). Decision height is given in feet above the runway threshold. Both serve the same function — they just use a different reference. The pairing DA/DH appears together on charts because some approaches publish one, some the other, and some both.
Why Pilots Care
It is the last safe point to commit to landing or go around, directly protecting against controlled flight into terrain in low visibility.
Grounding Statement
In cloud, when the altimeter reaches DA/DH, the pilot must either see enough to continue safely or begin the climb-away procedure.
Intuition Check
Decision does not mean this is the time to start thinking about what to do; the decision must be made immediately at that point. Altitude is read from the altimeter above sea level; height is measured above the runway reference for the approach.
Example Sentence 1
Approaching the DA on the ILS, the pilot caught sight of the approach lights and continued to land.
Example Sentence 2
Without the required visual references by DH, the crew immediately executed the missed approach.