Airworthiness Directives; The Boeing Company Airplanes

We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 787-8 airplanes. This proposed AD was prompted by reports indicating that the ram air turbine (RAT) assembly may fail to operate if deployed at low airspeeds. This proposed AD would require replacing either the RAT pump and control module assembly or the entire RAT assembly. We are proposing this AD to prevent failure of the RAT assembly to operate at low air speeds. The volume fuse on the RAT assembly may be activated in-flight before the RAT is deployed. This may lead to improper pump hydraulic pressure offloading when the RAT is needed. Failure of the RAT to operate in an all engine out event would result in loss of control of the airplane.