The FAA has traditionally published a diagram illustrating an effect of added weight as opposed to the loss of lift. This is nonsense. We have known for decades that the added weight is inconsequential...how much weight have you lost through the fuel burned while you are trying to figure out how much weight the ice has added? The only guy who needs to worry about the weight of accumulated ice is a Zeppelin captain. The loss of lift...and the aerodynamic effects on handling...are by far the more serious effects.