Decision Altitude VS. Minimum Descent Altitude

Its easy to munge DA and MDA into the single concept of minimums. Yet, decision altitude (DA) and minimum descent altitude (MDA) are very different concepts. As the names suggest, DA is a decision point while MDA is the lowest altitude allowed without visuals.

jmiller

Tuesday, May 10, 2016 at 12:00 AM ET

Verified

Key Takeaways:

Decision Altitude (DA) for precision approaches is a decision point where a missed approach must be initiated if visual references are not established, benefiting from obstacle clearance below DA for the maneuver.
Minimum Descent Altitude (MDA) for non-precision approaches is the lowest authorized altitude without visuals, which cannot be descended below, and the missed approach point (MAP) is typically further along the course.
Modern non-precision approaches increasingly utilize Constant Descent Final Approach (CDFA) with a Derived Decision Altitude (DDA), adding a buffer to the MDA to provide a DA-like decision point for timely go-arounds, though the procedural MAP remains fixed.
Successfully executing a go-around or missed approach requires prompt, smooth action, mental preparation, and awareness of factors like spatial disorientation (e.g., somatogravic illusion) to ensure a safe climb.

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It’s easy to munge DA and MDA into the single concept of minimums. Yet, decision altitude (DA) and minimum descent altitude (MDA) are very different concepts. As the names suggest, DA is a decision point while MDA is the lowest altitude allowed without visuals.

The difference between DA vs MDA is reflected in the regulations, Practical Test Standards (PTS, soon Airman Certification Standards) and TERPS. Without required flight visibility and runway environment, 91.175 says we can’t go below MDA. Yet, for an approach with a DA/DH, the rules only say an approach cannot be continued.