Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, and -500 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-100, -200, -300, -400, and -500 series airplanes, that requires repetitive inspections to detect galling on the input shaft and bearing of the standby rudder power control unit (PCU), and replacement of the standby rudder actuator with a serviceable actuator, if necessary. This amendment also requires eventual replacement of the input bearing of the standby PCU with an improved bearing, which constitutes terminating action for the inspections to detect galling. This amendment is prompted by a review of the design of the flight control systems on Model 737 series airplanes. The actions specified by this AD are intended to prevent galling on the input shaft and bearing of the standby PCU, which could result in uncommanded movement of the rudder or increased pedal forces. These conditions, if not corrected, could result in reduced controllability of the airplane.