InTgreen,
Good advice, check the ODM, for military pilots, RFM (Rotorcraft Flight Manual) for civvies.
On occasions (obviously, in an IFR equipped twin) I have no option but to fly above cloud. It's not an OEI performance issue for our aircraft at UK operating altitudes (avoiding the airways system above would be more of a problem). Sometimes, if there is an inversion, it is possible to find warmer air above icing cloud and for ice formed in the climb to disperse, but I wouldn't like to bet my life on it. I for one would never climb more than a couple of thousand feet above normal cruise altitude at the very most to try to get above icing cloud (see my previous post).
Having had one bad scare over thirty years ago, at night, in a military fixed wing single, I know how rapidly icing can build up and how severe the effects can be on an airframe and a turbine engine (we got as far as carrying out pre-ejection drills).
Imperative to plan carefully, (in UK the Met Office's F214 is a big help), avoid high ground altogether if necessary, monitor the OAT gauge and stop the climb before you get caught in situation where you might have no option but to enter freezing cloud. Know the en route minimum safe altitude at all times and be prepared to descend to it. If the in flight situation means turning back or diverting elsewhere, do it.
Sometimes the worst ice occurs on the ILS, because of the icing level; then you may have a big problem!