Airworthiness Directives; Boeing Model 737 Airplanes

The FAA is adopting a new airworthiness directive (AD) for all Boeing Model 737 airplanes. This AD requires repetitive measurement of the freeplay of both aileron balance tabs; repetitive lubrication of the aileron balance tab hinge bearings and rod end bearings; and related investigative and corrective actions if necessary. This AD results from reports of freeplay-induced vibration of the aileron balance tab. 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 loss of control of the airplane.