Underfire:
I don't want to get into an endless debate here, but a DA does mean that the decision to GA must be made no lower than that Decision ALT, and the procedure design criteria allows for the fact that the aircraft will sink below that alt when performing the GA. Obviously this is different from an MDA for NPAs where the decision to GA must be made well prior so that the aircraft does not bust the Min Desc ALT.
Peekay4:
Thanks - I know it does happen on the odd occasion due to the specific set of circumstances and confluence of the terrain and obstacle environment. In this case based on what I see from the charts in this thread (without investigating in more detail, which I'll never find time to do) I still find it a little strange.
For example, I can see that the LOC only has two DFs, but it's only the one at D4.0 LCO that facilitates the MDA to be down to 820ft (the fix at D1.1 LOC is beyond the MDA on glide @ 3.1°), so I cannot see an obstacle prior to 4NM being the cause of the relatively high DAs for the ILS (even with a slightly lower GS angle of 3.0° - which is a difference of 0.175% of 10.6ft/NM (so the additional margin of 40ft over 4NM or 50ft over 5NM may be influential?)).
Considering the Cat II APCH has a minimum CG of 5% for the missed, and the NPAs (LOC only and VOR) both have MAPts ≥1NM prior to the THR, I suspect that it's actually obstacles in the early phase of the missed that could be influential on the Cat I ILS minima (even without raising the GS by 0.1°).
Of course without knowing the specifics I could be laughably wrong
?
Regardless, if this was in my area of control, I'd seriously look at the feasibility and possible safety benefits (not to mention perhaps better Cat I ILS minima) of redesigning and recalibrating all procedures and landing aids (ILS, PAPI) so that the GS of all approaches was consistent - even at 3.1°.
And I'll take a look at KRNO one day out of curiosity.
Cheers