The Beechcraft 1900, in addition to the usual wings and vertical and horizontal stabilizers, and the extra vertical tail surfaces added for improved directional stability, has a pair of horizontal tail surfaces, called "stabilons", on the sides of the rear fuselage (not to be confused with the 1900's actual horizontal stabilizers, which are mounted atop the vertical stabilizer in a T-tail configuration):
(The stabilons of these two 1900Ds are circled in green to avoid confusion with the shadows of their horizontal stabilizers on the ground. Image by ERIC SALARD at Flickr, via russavia at Wikimedia Commons, cropped by Marc Lacoste at Wikimedia Commons, annotated by me.)
How, exactly, do the stabilons operate? Are they fixed structures? Do they move up and down to trim the aircraft? Do they move along with the elevators when the pilot commands a pitch input?