There is no dual engine HV chart in any twin engine helicopter I'm aware of. The reason is that the engines have enough isolation that no single failure should be able to take both engines out at the same time.
And if there was a dual engine HV chart, you wouldn't want to know how large it would be...
A benefit of having two engines.
Thank you Shawn. For some strange reason I found your post today.
If I understand correctly, than there is no safe procedure for a T/R failure in a hover, lets say under 500ft AGL? I remember a japanese 135 video crashing while at slow speed, low height maintenance flight.
I'm asking about this because my colegues retured from 135 sim with an idea about this. After fenestron failed in a hover 1500ft AGL they tried gaining airspeed while spinning and 1500ft wasn't enough height-red screen. Than they encountered the same situation, stopped spinning by rolling off the twist grips, entering autorotation, gaining airspeed and while at more than 65kts, roll back on the twist grips and you have T/R fail during cruise flight scenario - more survivable. They lost about 1000ft height during that maneuver.