Summary
This document revises an earlier proposed airworthiness directive (AD), applicable to all Boeing Model 737-100, -200, -300, - 400, and -500 series airplanes, which would have superseded an existing AD that currently requires either leak tests of the forward lavatory service system, and repair, as necessary; or draining the system and placarding the lavatory inoperative. That proposed AD would have provided an option for accomplishing terminating action for certain leak tests. It would have required leak tests of other lavatory drain systems; installation of a cap or vacuum break on the flush/fill line; and either periodic replacement of the seal for the cap and tank anti- siphon valve or periodic maintenance of the vacuum break in the flush/ fill line. This action revises the proposed AD by removing the terminating action; requiring periodic changing of the seals of certain lavatory drain systems; replacing ``donut valves'' with other FAA- approved valves; revising certain leak test intervals; and revising the pressurization and fluid level requirements for testing. 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.