In IMC or less than 4100-3 conditions you need to plan it on one engine. FAR-25 requires that you can meet all then performance.
If you can't climb 815'/nm one engine, accept the clearance, depart and lose one at V1 or shortly there after your f*cK#d. You've placed yourself in a position, IMC and climbing slower than the terrain, that can't be won.
That's what I thought. It is my understanding that as we fly Part25 aircraft, we MUST consider all planning from V1 to the enroute portion (or a doable alternative) with one engine out.
But, I see folks launching in aircraft that I KNOW barely make gradient on all engines. It's a good thing turbine engines are so reliable. I am just waiting for the day when we wake up and see where someone put a Beechjet or Citation into the side of that mountain.
But, if one takes into account unused runway (pretty significant on some aircraft), and figures total gross climb to 12000MSL/2539'AGL which includes the last 1000' in the enroute climb configuration there may be a way to meet it. The enroute climb (that is the post-1500AGL, clean wing, engines at MCT portion) is usually a much better than second, third, and final segment.
It is my understanding, also, that holding V2 to 2539'AGL isn't acceptable per FAA. V2 only exists as high as the manufacturer's charts (either 400AGL, 1000AGL, or 1500AGL). Also, not a good idea because enroute climb data is almost always better than second segment, despite having a much lower Part25 requirement.