Airworthiness Directives; Boeing Model 757 Airplanes

The FAA is adopting a new airworthiness directive (AD) for all Boeing Model 757 airplanes. This AD requires repetitive measurements of the freeplay of each of the three power control units (PCUs) that move the rudder; repetitive lubrication of rudder components; and corrective actions if necessary. This AD results from a report of freeplay-induced vibration of the rudder. The potential for vibration of the control surface should be avoided because the point of transition from vibration to divergent flutter is unknown. We are issuing this AD to prevent excessive vibration of the airframe during flight, which could result in divergent flutter and loss of control of the airplane.