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) and Minimum Descent Altitude (MDA) are distinct concepts: DA is a decision point for precision approaches to initiate a missed approach if visuals are absent, while MDA is the absolute lowest altitude allowed for non-precision approaches without visual references.
Precision approaches require prompt initiation of a missed approach at DA, acknowledging that some altitude loss will occur during the maneuver, and cautioning against spatial disorientation like the somatogravic illusion.
Non-precision approaches are transitioning to Constant Descent Final Approach (CDFA) using a Derived Decision Altitude (DDA) (MDA plus a buffer) to facilitate a safe missed approach above the MDA, while the official missed approach point (MAP) remains crucial for terrain clearance.
Pilots must consistently practice and mentally review go-around/missed approach procedures, ensuring smooth and timely execution to counteract expectation biases and avoid common errors.

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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.