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* to initiate a missed approach if visual references are not met, allowing for some altitude loss during the maneuver due to obstacle clearance designed below it.
Minimum Descent Altitude (MDA) for non-precision approaches is the *absolute lowest* altitude permitted, which must be maintained until the Missed Approach Point (MAP) if visual references are not established.
For non-precision approaches, the Constant Descent Final Approach (CDFA) technique, which involves calculating a Derived Decision Altitude (DDA) above the MDA, allows pilots to fly these approaches more safely by initiating a missed approach *before* descending to the actual MDA.
Pilots must regularly practice or mentally review go-arounds and missed approaches due to their infrequent real-world execution, ensuring prompt, smooth execution while counteracting psychological biases and potential spatial disorientation.

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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.