Airworthiness Directives; Saab Model SAAB SF340A, SAAB 340B, and SAAB 2000 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Saab Model SAAB SF340A, SAAB 340B, and SAAB 2000 series airplanes, that requires 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 amendment 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 this 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 consequent reduced controllability of the airplane.