Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 747-100, -200, - 300, -SP, and -400F series airplanes. Among other things, this proposal would require repetitive leak checks of the lavatory drain system and repair, if necessary; installation of a cap or flush/fill line ball valve on the flush/fill line; would require periodic seal changes; and replacement of any ``donut'' type valves installed in the waste drain system. 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 damage to engines, airframes, and property on the ground that is associated with the problems of ``blue ice'' that forms from leaking lavatory drain systems on transport category airplanes and subsequently dislodges from the airplane fuselage.