While carrying out such mountain rescue in a AW-139 what performance graphs are normally used ?
HIGE or HOGE at MCP / TOP or intrapolate in between ?
If the data is not depicted on the graph.....you cannot "interpolate".
Use the appropriate graph and see what it provides for the conditions extant and that is your "limit".
Looking into the
blank area and
guessing what might be is a sure way of getting into trouble.
I would have looked at HIGE, HOGE, and OEI charts and determined each weight for the conditions at the landing site.
Plainly OEI would result in a serious negative vector at that elevation but it would be nice to know how far down the mountain you would have to get to fly away (or not).
Then upon arrival at the scene I would have done a proper Recon.....confirming the wind direction and best approach path....and do a power check in calm air to confirm what power was actually available.....then carry out the landing or reject the effort if there was insufficient power.
Interpolate is not the word I would use....but considering the HOGE and HIGE weights would allow you to see the difference in performance between the two and let that be a factor in your evaluation of the conditions of the landing area re blowing snow, depth of snow, risk of falling through the snow pack, and that kind of thing.
Keeping some reserve power for unknown contingencies during Scene Landings never hurts.