What is the purpose of the extra horizontal and vertical surfaces on the tail of the Beechcraft 1900?
Yes that is what is the most cost effective solution after flight testing has demonstrated that the vertical tail surface has to be increased for instance. The little winglets at the end of the horizontal tail do increase aerodynamic efficiency of the stab - plus they just look cool.



The BAe 125 stuck a bit of fin on top of the original fin design, the Beech 1900 added the extra vertical tail surface underneath the aft fuselage cone, in the form of 2 v-shape surfaces which also help the total horizontal tail area.