Summary
This document revises an earlier proposed airworthiness directive (AD), which would have superseded an existing AD that is applicable to certain Boeing Model 737-100, -200, -300, -400, and -500 series airplanes. The existing AD currently requires an inspection of reworked aileron/elevator power control units (PCU's) and rudder PCU's to determine if reworked PCU manifold cylinder bores containing chrome plating are installed, and replacement of the cylinder bores with bores that have been reworked using the oversize method or the steel sleeve method, if necessary. This action, among other items, revises the previously proposed rule by expanding the applicability of the existing AD to include airplanes equipped with certain rudder PCU's. The actions specified by this new proposed AD are intended to prevent a reduced rate of movement of the elevator, aileron, or rudder due to contamination of hydraulic fluid from chrome plating chips; such reduced rate of movement, if not corrected, could result in reduced controllability of the airplane.