How is DDA derived?

• A. MDA + 50
• B. MDA - 50
• C. MDA + 100
• D. MDA

Answer: (A)

DDA is found by adding a fixed safety margin to the minimum descent altitude. In this context, the standard way to derive the decision altitude is to take the MDA and add 50 feet. That extra height gives you a clear point to decide whether you can continue visually or must initiate a missed approach, accounting for small errors in altitude indication, equipment tolerances, and the time you need to react. Lowering below the MDA or keeping it equal to the MDA would remove that protective buffer, and adding a larger amount (like 100 feet) isn’t the typical derivation used in this scenario.