what terrain clearance do you provide in the missed approach procedures you design, or do you put the "required" gradient on the chart?
The charts that I provide are certainly custom. They are RNP transition to a GBAS final, or just RNP. With the custom, all is coded, the missed approach and EO missed are coded, and therefore the alignment is reflected on the chart, if allowed by the regulator. SID and EO departures are shown on different plates.
Typically, the charts have a set DA/MDA, required gradients are not shown on the chart, as the entire procedure is coded in, and the procedures are custom designed for the aircraft.
The approach, same as the public criteria, is based on the coldest day of that airport (ie lowest effective GPA) with the required ROC.
The missed is based on the hottest day, max landing weight based on the elev/performance, etc to get the min net per the criteria.
Now, I do have charts with performance DA's. This is a specialty of my firm, operations based navigation, hence the name.
These procedures are based on the missed AND the required gradient is provided. The approach is still the same basis as above, but the missed is based on a real time performance for the aircraft/airport. So if the operator, based on weight/temp/etc determines the climb grade, at 6.5%, this is the DA/vis required. These CG range from the criteria 2.5% up to 12%. This design does not include any EO missed, that is separate.
For the obstacle clearance, where to begin...
Depends on several factors, rad alt, baro, head loss, and momentary descent for the particular aircraft, latency, exposure time, prox and regulators.
For all engine, the respective criteria clearances are used. This somewhat assures that the state is maintaining the obstacle database, and from a liability perspective, I consider this the BARE minimum.
For EO, I try to use the criteria obstacle surfaces, but can fall back to the 35 foot min with turn additives, etc. Turn additives and winds are significant factors in obstacle clearances. There are also mountainous and precipitous terrain additives
Another big factor is the respective aircraft and the prox warnings...some regulators allow for a prox warning on EO, others do not. a Smiths/Honeywell/thales/etc all have different settings for the warning, so that is really a wildcard in the design.
So...long story short, there is a combination of many factors when looking at a 'clearance' in the design. Clearances can be real of assumed additives.
The coded procedure has met the approval of all of the applicable minimums and worst case scenario given.