Airworthiness Directives; McDonnell Douglas Model DC-9-10, -20, -30, -40, and -50 Series Airplanes; and C-9 Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9-10, -20, -30, -40, and -50 series airplanes; and C-9 airplanes; that requires repetitive visual and x-ray inspections to detect cracks of the upper and lower corners and upper center of the door cutout of the aft pressure bulkhead; corrective actions, if necessary; and follow-on actions. For certain airplanes, the amendment also requires modification of the ventral aft pressure bulkhead. The actions specified by this AD are intended to detect and correct fatigue cracks in the corners and upper center of the door cutout of the aft pressure bulkhead, which could result in rapid decompression of the fuselage and consequent reduced structural integrity of the airplane. This action is intended to address the identified unsafe condition.