Airworthiness Directives; Boeing Model 737 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to all Boeing Model 737 series airplanes, that requires repetitive displacement tests of the secondary slide in the dual concentric servo valve of the power control unit (PCU) for the rudder, and replacement of the valve assembly with a modified valve assembly, if necessary. This amendment is prompted by reports of cracking found in PCU secondary servo valve slides. The actions specified by this AD are intended to prevent failure of the secondary slide and consequent rudder hardover and reduced controllability of the airplane.