Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Model DC-8 series airplanes. Among other things, this proposal would require repetitive leak tests of the lavatory drain systems and repair, if necessary; installation of a lever lock cap, vacuum breaker check valve or flush/ fill line ball valve on the flush/fill line; periodic seal changes; and replacement of ``donut'' type waste drain valves installed in the waste drain system. This proposal is prompted by continuing reports of damage to engines, airframes, and 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.''