Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747-400, 747-400D, and 747-400F series airplanes. The existing AD currently requires reviewing airplane maintenance records; inspecting the yaw damper actuator portion of the upper and lower rudder power control modules (PCM) for cracking, and replacing the PCMs if necessary; and reporting all airplane maintenance records review and inspection results to the manufacturer. This proposed AD would expand the applicability and discontinue certain requirements of the existing AD. This proposed AD would require repetitive inspections of the PCMs and replacement of the PCMs if necessary. This proposed AD results from manufacturer findings that the inspections required by the existing AD must be performed at regular intervals. We are proposing this AD to detect and correct cracking in the yaw damper actuator portion of the upper and lower rudder PCMs, which could result in an uncommanded left rudder hardover, consequent increased pilot workload, and possible runway departure upon landing.