LSM, just because it is legal does not make it safe. Most regulators in the world at the moment are struggling to have the experience to make informed decisions on such matters. We have been watching the European proposition to convert MDA's to DA's for a while now, and to be honest I don't agree with it.
So I'll leave the decision on this up to you. PANS-OPS says that in the final approach segment I must give you 246ft of obstacle clearance. The MDA is derived by giving you at least 246ft of obstacle clearance from all obstacles. If you convert the MDA to DA with no additional allowances then basically you have (246ft - height loss) clearance from obstacles. For a CAT D aircraft height loss is 161ft (PANS-OPS published height loss) As you can see adding 50ft to a minima to turn it into a DA doesn't seem quite adequate does it??
a) If you want 246ft clearance from obstacles (IAW PANS-OPS) I strongly suggest you don't descend below MDA.
b) If you are happy with down to 85ft of obstacle clearance, then punch on through the MDA at hearts content.
Which one do you think is right?
But do all the procedure designers in the world a favour....if you choose option (b), and the DA was simply converted from an MDA, when you hit something, don't point the finger at us and accuse us of not protecting you.
Sorry if this seems harsh, but there are alot of people running around at the moment claiming to know what they are talking about. When there is smoking hole in the ground, they all dissappear.