Definition
An altitude established by an operator on a non-precision approach, set above the published Minimum Descent Altitude (MDA), at which the pilot must decide to continue the approach to landing or execute a missed approach. The DDA is calculated to ensure the aircraft does not descend below the MDA during the missed approach maneuver.
Plain English
On approaches that don't have a normal decision point, some operators add their own. They pick an altitude a little higher than the lowest legal altitude on the approach, and treat that as the go/no-go point. The buffer keeps the aircraft from accidentally dipping below the legal minimum while pulling up for a missed approach.
Context Anchor
Seen when planning or briefing a nonprecision instrument approach that will be flown as a steady descent rather than by leveling off at the minimum altitude.
Derivation
"Derived" because the altitude is derived (calculated) by the operator rather than published on the approach chart. "Decision Altitude" mirrors the term used on precision approaches, where a single altitude triggers the land-or-go-around decision.
Why Pilots Care
Provides a safe, adjusted go/no-go point when standard published altitudes do not fully account for current temperature or pressure effects.
Grounding Statement
Picture descending in cloud toward the airport: the DDA is the point where you decide early enough to climb away before reaching the lowest allowed altitude.
Intuition Check
Do not treat DDA as permission to descend below the published minimum. It is an earlier decision point above that minimum, used to help keep the aircraft from going below it.
Example Sentence 1
Company procedures require us to use a DDA of 50 feet above the published MDA on all non-precision approaches.
Example Sentence 2
For the RNAV approach the DDA was set 40 feet higher than the published DA to compensate for cold temperature.