The procedure where the missed approach alt is set after reaching MDA has a couple of disadvantages. 1: You have to round up your MDA to the nearest hundred because that's the increments in the MCP alt window. 2: You will get alt acquire before reaching MDA, and therefore the decision whether or not to continue is taken earlier and therefore higher.
The difference in go around initiation altitude between the two procedures
(1: Setting your MDA at FAF, 2: Setting Mis App alt at FAF) can be more than 200 feet, depending on your ROD.
I know some will argue that if you have a high ROD at MDA you will certainly go below, and I agree.
However, that will apply to an ILS approach as well. The Jar-Ops state that you may continue down to DA/H or MDA/H, but you will have to go around if you don't acquire the required visual reference at that point. So you are actually allowed to "bust" your minimums
, as long as you initiate the go-around before reaching either DA/H or MDA/H. That's what the different minimums (according to category) are for. The Jar-Ops state the system minimums, and then there's a wide range of factors listed, among them: The OCH/OCL for the category of aeroplane, which takes into account the height loss for the category and that is added to your system minimum. That's why some operators can get down, while others are diverting when the WX is crappy.
Allright, over to you now...
