DH and MDA
Hi there,
I've never heard of a DA, may be you're confused between DH and MDA. The first one is use with precision appch, mainly ILS or MLS (which i've never seen). The DH is decison height at which you must start a missed appch if you don't have visual with the proper ground reference (it can be the runway or the proper light). the MDA is pretty different , it's the minimum descent altitude and it's used with non-precision appch (ndb, ndb/vor, vor etc). The main difference is that you don't necesarily have to initiate a missed apch upon reaching this altitude with no visual to the ground. Depending on the appch you may descend to this altitude and then keep on flying til a certain DME point or any other MAP. For example you may descend to the MDA within 7 NM from threshold and the MAP could be at 1 DME from threshold. It will never be the case for a DH because following the glide and the loc will bring you to a unique point : the MAP.