Definition
DA has two distinct aviation meanings. (1) Direct Access: a method of obtaining flight or weather information directly from a source system without going through an intermediary service. (2) Decision Altitude (DA) / Decision Height (DH): on a precision or approach-with-vertical-guidance instrument approach, the specified altitude or height at which the pilot must decide either to continue the approach to landing — because the required visual references are in sight — or to execute a missed approach. Decision Altitude is referenced to mean sea level (read from the altimeter); Decision Height is referenced to the height above the touchdown zone or runway threshold.
Plain English
DA can mean two different things. One is 'direct access,' which simply means getting information straight from the source. The other is 'decision altitude' or 'decision height' — the point on an instrument approach where the pilot must look up and decide: can I see the runway well enough to land, or do I need to climb away and try again?
Context Anchor
Seen in FAA acronym lists, approach procedure discussions, instrument approach charts, and operational material where the surrounding words tell you which meaning of DA is intended.
Derivation
Decision' comes from Latin decidere, 'to cut off' — at this altitude the choice is cut off and must be made: land or go around. 'Direct' comes from Latin directus, 'straight' — straight to the source, no middleman.
Why Pilots Care
It sets the last safe point to commit to landing or go missed, directly affecting safety in low-visibility conditions.
Intuition Check
Do not assume DA has only one meaning. In a systems or information context it may mean direct access; on an instrument approach it usually means decision altitude or decision height.
Example Sentence 1
On the ILS approach, the pilot reached decision altitude, saw the approach lights clearly, and continued to land.
Example Sentence 2
Reaching DA without the runway in sight, the crew immediately executed the missed approach.