Airworthiness Directives; McDonnell Douglas Model DC-9-81 (MD-81), DC-9-82 (MD-82), DC-9-83 (MD-83), and DC-9-87 (MD-87); Model MD-88 Airplanes; and Model MD-90-30 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9-81 (MD-81), DC-9-82 (MD-82), DC-9-83 (MD-83), and DC-9-87 (MD-87); Model MD-88 airplanes; and Model MD-90-30 series airplanes; that requires installation of a pipe support and clamps on the hydraulic lines in the aft fuselage; replacement of the hydraulic pipe assembly in the aft fuselage with a new pipe assembly; and installation of drain tube assemblies and diverter assemblies in the area of the auxiliary power unit (APU) inlet; as applicable. This amendment is prompted by reports of smoke and odor in the passenger cabin and cockpit due to hydraulic fluid leaking into the APU inlet, and subsequently, into the air conditioning system. The actions specified by this AD are intended to prevent such hydraulic fluid leakage due to fatigue vibration and cracking in the flared radius of a hydraulic pipe in the aft fuselage, which could result in smoke and odors in the passenger cabin or cockpit.