The DC8/9 family had tail deicing for the removal of ice at low speeds in the terminal area.The DC8 stipulated that if icing was suspected ,on the tail, then the tail deicing button(when pressed )dedicated all the heat to said surfaces for 3 mins.To be off by the outer markers to avoid run back icing on the grouns(unheated areas).The Douglas products,as opposed to Boeing had smaller size tail(stab) areas-hence the heating req'Boeing had no deicing heat on the tail surfaces (B727/747)as they had suficient area to support the weight.This question was raised ,with the developement of the MD11,and MD elected to stay with the smaller tail surface for lower drag/higher speed..
