Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 737-100, -200, - 300, -400, and -500 series airplanes. This proposal would require installation of a placard that warns the cabin crew not to put the selector valve for the forward lavatory water supply in the ``DRAIN'' position during flight. This proposal also would require installation of an isolation valve in the drain line downstream of the selector valve. This proposal is prompted by reports of damage to the horizontal stabilizer and engine flameout caused by ice formed from water drained inadvertently through a mispositioned selector valve. The actions specified by the proposed AD are intended to prevent damage to the engines, airframe, or horizontal stabilizer, and/or prevent a hazard to persons or property on the ground, as a result of ice that could dislodge from the airplane.