Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to McDonnell Douglas Model DC-9 and DC-9-80 series airplanes, Model MD-88 airplanes, and C-9 (military) series airplanes. This proposal would require repetitive high frequency eddy current inspections of the external areas of the fuselage to detect cracks of the skin and/or longeron, and various follow-on actions. The proposal also would require the installation of a preventative modification, which would terminate the repetitive inspections. This proposal is prompted by reports indicating that, due to material fatigue caused by installation preload and cabin pressurization cycles, fatigue cracks were found in the skin and longerons of the fuselage. The actions specified by the proposed AD are intended to prevent such fatigue cracks, which could result in loss of the structural integrity of the fuselage and, consequently, lead to rapid depressurization of the airplane.