Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed AD would require replacing or modifying the upper and lower rudder power control modules (PCM). This proposed AD was prompted by a report of a rudder hard-over event on a Model 747-400 series airplane, caused by a rudder PCM manifold cracking and separating in the area of the yaw damper cavity end-cap. We are proposing this AD to prevent a failure of the lower or upper rudder PCM manifold, which could result in a hard-over of the rudder surface leading to an increase in pilot workload and a possible high-speed runway excursion upon landing.