Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all McDonnell Douglas DC-9 and DC- 9-80 series airplanes, and Model MD-88 airplanes. Among other things, this proposal would require repetitive leak checks of the lavatory drain system and repair, if necessary; would provide for the option of revising the FAA-approved maintenance program to include a schedule of leak checks; would require the installation of a cap on the flush/fill line; and would require replacement or modification of the vent system piping. This proposal is prompted by continuing reports of damage to engines and airframes, separation of engines from airplanes, and damage to property on the ground, caused by ``blue ice'' that forms from leaking lavatory drain systems on transport category airplanes and subsequently dislodges from the airplane fuselage. The actions specified by this proposed AD are intended to prevent such damage associated with the problems of ``blue ice.''