vikena,
A lot of what you say is feasible, but there are a number of important considerations that you must make. Here's a few -
(1) "
A depature procedure requires an all engines op gradient of 3.3%",
OR MORE if required for the depature routing.
(2) There is 0.8% 'fat' built into the SID 3.3% gradient, so you would need to extract performance data applicable to 2.5% Net Gradient, or the SID Gradient minus 0.8% if higher than 3.3%
(3) The SID gradient commences at the end of the runway, whereas the 2nd segment for OEI performance commences at the end of the 1st Segment. You will have to ensure that the 1st Segment lies ENTIRELY above the Runway and the SID Gradient from the end of the runway. This will mean reducing your Runway Effective Operational Length by a considerable amount. You'll have to do some trigonometry for Runway Slope, SID Gradient, and 1st Segment Length and Gradient. (That's going to be the most difficult part).
(3) You'll need discrete obstacle data within the SID coverage area to ascertain the Acceleration Altitude (3rd Segment), and this is generally not available. If it's not available, you'll have to use the Altitude at which the SID Gradient requirement terminates, or the MSA. If MSA was, for example, 7000 feet, you'd have to use this as the Acceleration Altitude. Do you have enough time to conduct a OEI Climb to 7000 feet, and complete your 3rd segment acceleration to Clean-Up within the 5 or 10 minute limit at Takeoff thrust? Actually, in converting the PANS-OPS obstacle clearance criteria to FAR25 (or it's equivalent) you need not go all the way to the MSA. In this case you can use -
Acceleration Altitude = Airport Elevation + (MSA - Airport Elevation - 1000) X 3.3 / 2.5 + 35.
(4) If you can't make MSA within the Takeoff thrust time limit as specified in (3), then you'll need discrete obstacle data AGAIN to ascertain a suitable 'break-off' point from the SID to an area where the FAR25 obstacle clearance requirements can be satisfied.
There's a 'Starter Kit' for you.
There are a great number of SIDs that start earlier than what would be desired for optimal obstacle clearance under OEI FAR25 rules (e.g. The SID (3.3%) requires a turn at Runway End, the OEI procedure (2.4%) requires Runway Track to 7.0 DME). This leaves the pilot in a 'Grey' area if suffering an engine failure after commencing the SID. In these cases, it has been necessary for me when developing Engine Failure 'Escape Routes', to provide a second, more limiting' OEI procedure to be followed if the SID is to be followed. With these options, the pilot is then, before Takeoff, commited to either the standard OEI Escape Route at the optimum weight, or the SID, at a reduced weight. In developing these secondary 'SID OEI Escape Routes', all of the factors listed above have to be considered.
Lots of luck with the project,
Old Smokey