We are adopting a new airworthiness directive (AD) for all The Boeing Company Model DC-9-81 (MD-81), DC-9-82 (MD-82), DC-9-83 (MD-83), DC-9-87 (MD-87), and MD-88 airplanes.
This AD was prompted by reports of cracks of the hinge bearing lugs of the center section ribs of the horizontal stabilizer. This AD requires repetitive high frequency eddy current (HFEC) inspections for cracking of the left and right rib hinge bearing lugs of the aft face of the center section of the horizontal stabilizer; measuring crack length and blending out cracks; and replacing the horizontal stabilizer center section rib, if necessary.
We are issuing this AD to detect and correct cracking in the hinge bearing lugs of the horizontal stabilizer center section ribs, which could result in
failure of the lugs, and consequent inability of the horizontal stabilizer to sustain the required limit loads and loss of control of the airplane.