OzExpat,
I WAS nervous about putting that one in without further explanation, and you caught me out, I should have been more specific. Yes, I concede that the SIDs already do have the Gross/Net factor built in, BUT, and it's a big BUT, simply applying AFM data to provide for a 3.3% climb gradient would not be enough because of the 1st segment. An aircraft just capable of complying with 3.3% with gear up (upon which 2nd segment is based), would fall below 3.3% in the first segment. TYPICALLY 1st Vs 2nd segment delta is about 0.8%, coincidently in line with the Gross Vs Net delta for the 2nd segment for a 2 engined aircraft. Crude - Yes!, but adding the 0.8% and taking advantage of the increased PANS-OPS clearances Vs the FAR25 clearances should come close to a reasonable compromise. Please remember the tone of my suggestion, i,e, at least if you're going to do this, then do SOMETHING about making provision for consequences of engine failure. Some 1st segments are very long, and some SIDs have their worst gradients close-in.
BTW, I sometimes use PANS-OPS data, reduce it to the actual obstacles that enforced the PANS-OPS requirements, and re-apply the FAR25 obstacle clearance criteria. A bit lazy, definately safe, and perfectly acceptable if the obstacles aren't too limiting.
Thanks for keeping me honest,
Old Smokey