You are not allowed to descend more than 15% to have a constant margin to be protected from obsracles
What is wrong with the step by step schematic is that occasionaly (tired pilot, error, etc.) the pilot may think he is allowed to pass D10.0 aswell at 3000' or 2000', D7.0 aswell at 2000' or 1300'. The red line is the real bottom step by step path. BUT it is possible that the pilot descending the CDA does the same fatal mistake... So charts' drawers would not draw square steps but figure the 15% slopes with the distances. So the confusion is no more possible. The confusing grey zone exist already in the official documents about approach path design.
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I did a mistake calculating the average position where you cross the CDA path at MDA 490' : The distance to AD is 2.0 NM and not 2.8 NM. Please correct.)
