Summary
We are revising an earlier proposed 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. That NPRM proposed 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. That NPRM was prompted by reports of cracks of the hinge bearing lugs of the center section ribs of the horizontal stabilizer. This action revises that NPRM by adding the requirement for rib replacement if cracking is found during certain inspections of this proposed AD. We are proposing this supplemental NPRM 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, resulting in theinability of the horizontal stabilizer to sustain the required limit loads and consequent loss of control of the airplane. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.