What is the difference between DH and MDA in approach minima?

• A. DH is used for non-precision; MDA for precision.
• B. DH equals MDA; both used interchangeably.
• C. DH is altitude above the runway; MDA is below sea level.
• D. DH is used for precision approaches; MDA is used for non-precision approaches.

Answer: (D)

The key idea is how decision points are defined when you’re following an instrument approach, depending on whether vertical guidance is available.

On a precision approach, you have vertical guidance that guides you down the glide path. You descend as you’re cleared, and you reach a decision height. At that height above the runway threshold, you must decide to land if you have the required visual references; if you don’t, you go around. Because vertical guidance is provided, there’s a specific height at which you must either continue to land or initiate a missed approach.

On a non-precision approach, there is no vertical guidance. You descend to the minimum descent altitude, which is the lowest altitude you may level off at on final. You must maintain that altitude until you either establish the required visual cues to continue the approach and land, or you execute a missed approach if the cues aren’t present.

So the difference is that decision height is used with precision approaches that provide vertical guidance, while minimum descent altitude is used with non-precision approaches that do not.