Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 737-100, -200, - 300, -400, and -500 series airplanes. This proposal would require removing the yaw damper coupler; replacing its internal rate gyroscope with a new or overhauled unit; and performing a test to verify the integrity of the yaw damper coupler, and repair, if necessary. This proposal is prompted by an FAA determination that requiring replacement of the internal rate gyroscope will significantly increase the reliability of the yaw damper coupler system. The actions specified by the proposed AD are intended to prevent sudden uncommanded yawing of the airplane due to potential failures within the yaw damper system, and consequent injury to passengers and crewmembers.