Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Saab Model SAAB SF340A, SAAB 340B, and SAAB 2000 series airplanes. This proposal would require repetitive operational tests of the pitch trim system of the elevator trim-tab of the flight control unit to ensure that the system operates correctly, and repair, if necessary. This proposal is prompted by a report of uncommanded movement of the right-hand elevator trim-tab to a maximum deflection position, which was apparently due to a failure in the aircraft harness and a fault in the pitch trim synchronizer. The actions specified by the proposed AD are intended to prevent such uncommanded movement of the elevator trim-tab, which could lead to structural overload of the horizontal stabilizers at speeds above 180 knots, and resultant reduced controllability of the airplane.