Definition
DA/DH is the specified altitude or height on a precision or approach-with-vertical-guidance instrument approach at which the pilot must decide whether to continue the approach and land or execute a missed approach. Decision Altitude (DA) is referenced to mean sea level and read from the altimeter. Decision Height (DH) is referenced to the height above the touchdown zone or runway threshold. To continue below DA/DH, the required visual references for the intended runway must be distinctly visible and identifiable, and the aircraft must be in a position to land using normal maneuvers.
Plain English
It is the point on the way down during an instrument approach where the pilot has to make a yes-or-no decision: if the runway environment is in sight and the aircraft is in a good position to land, continue; if not, go around and fly the missed approach.
Context Anchor
Seen on instrument approach procedures, including approaches to parallel runways, where pilots must know exactly when the landing decision point occurs.
Derivation
Decision' comes from the Latin decidere, meaning 'to cut off' — at this point on the approach, the pilot cuts off further descent unless the runway is in sight. The pairing DA/DH simply reflects two ways of expressing the same decision point: one read from the altimeter (altitude above sea level) and one expressed as height above the runway.
Why Pilots Care
Missing this point without visual contact risks controlled flight into terrain or runway incursions.
Intuition Check
Do not read DA/DH as a suggested altitude where you can keep looking a little longer. It is the decision point: continue only if the required visual cues are in sight and the landing can be made safely; otherwise, go missed.
Example Sentence 1
Approaching DA/DH on the ILS, the pilot saw the approach lights clearly and continued the descent to land.
Example Sentence 2
The approach plate listed the DA/DH as 1240 feet MSL with a 200-foot HAT.