Cap,
I wish it was that simple...
So if I use one of the "public" plates, then I just need to achieve 2.5%? I assume that will give me 35ft obstacle clearance up to the MSA.
The 35 feet is not based on a 2.5% CG, the 35 feet is based on SID, the min obstacle clearance plane is based starting at the end of the runway, sloping up, with a min CG gradient of 3.3% The aircraft is assumed, for criteria calculations, to be at least 35 feet above the end of the runway. This 'surface' is what one needs to clear.
If, and IF, you have a 2.5% CG with EO Missed Approach, it may work, but you have to look at all of the factors. (just dont turn for a while)
How do you present the gradient info to the operator so that they can work out the maximum weights for a procedure, or do you crunch the performance numbers for an EO and provide that data to the operator?
With a coded procedure, it is a combination of worst case factors...highest temps for the airport, bleeds, etc on performance...this generates a max weight. We have to remember that the procedure for the public criteria is based on an ISA delta. So we try to design a path, that extends the weight limits aside from the public procedure.
Designs are good for a certain temperature. You may have an airport where the ISA D is always high, and you will always be weight limited for that airport. This is something that the people back in the office are always calculating the load diagrams for that aircraft. (you think ATC has it tough, look at what these people do)
Your aircraft should not have been loaded higher, using the the real-time temp at the destination, than all of these factors.
I am not sure of the SOP on EO, but many airlines contract EO procedures, just so they can extend weight limitations past the required 2.5% CG.