Ice will get you unless you do it right

Flying in icing conditions is tricky but may be dealt with successfully if you keep the plane flying. Basically an airfoil that is covered with ice is very inefficient, producing less lift and lots of drag. As the icing increases things get very dicey such that one may be at the edge of stall and not know it. Also once the ice is on, it is most difficult if not impossible to get off, with the exception of rime ice on boots (sometimes but not always). That being the case it was the common wisdom not to do anything too drastic to alter the aerodynamics, that included not adding flaps or any sudden or extreme control surface movement.

So, what to do. If it is too late to climb out of the icing you better get down quickly. Since there is a lot of drag don't be afraid to add all the power you've got to keep from stalling. Your stall warning indicator should be heated to help you in this. Remember stall speeds are not what they were with a clean airfoil. If you are on approach, declare an emergency and expedite descent. Again, don't change the aerodynamics by adding flaps or dropping the gear early. Wait as long as possible to do the latter.
Using the the autopilot may be dicey as it will try to maintain heading , altitude and or glidesope irrespective of whats out there on the empennage and may put you in a stall. Therefore it would seem best not to engage it.

The moral then is to avoid ice, but if you are caught remember to keep the airspeed above stall anyway you can. Flying with ice is like pushing a baby carriage full of nitroglycerine. Better do it very carefully.