Hi FD, I absolutely agee that those are step down fixes. If you note the mast elevation 1074ft just prior to the D3.8 fix, add 247ft gives 1321ft, round that up to the next 10ft gives 1330ft which is the OCA until you pass D3.8. The later step down fixes are calculated in exactly the same way.
Now, lets pretend that that step down fix was provided by an NDB, the Final Approach Fix was provided by some other means, maybe a VOR (unlikely but stick with me) and all other step down fixes were DME based.
You could now publish two MDA(H)s:
with DME 650’(625’)
without DME 1330’(1305’)
However, if you have not got DME available for the approach that Boyington is asking about, then you can’t fly the approach as DME is required and if you do have DME, why would you ever stop the descent at 1330ft or 780’. Hence, why publish MDA for 2.8 D and 3.8D?
Now don’t get me started on why Jeppesen mention CDFA on their plates!! Time for another thread.
Cheers
Tees