From my limited brain,
H-V curves pertain to the ability to autorotate safely. If I recall, the S76 graph is titled something like "limiting heights and speeds AFTER an engine becomes inop." ???
Sorry to answer a question with a question, but how can the 139 not have an H-V graph? Is autorotation not part of the certification process? We've all youtubed the s92 auto' certification video!
Cat A guarantees OEI flyaway predicated on the WAT charts. I've never referenced the H-V graph when calculating CAT A performance....just the WAT chart!
Cat B has NO OEI flyaway guarantee and therefore treat it like a single engine a/c....i.e look for a place to land/reject along your path.
Interesting question! Makes me think.....brain hurting! must stop now!
DK