Applicability: Model 737-100, -200, -300, -400, and -500 series airplanes; having forward lavatories installed; certificated in any category.

Effective date: March 25, 1999

Compliance: Required as indicated in FAA AD 99-01-16.

99-01-16 BOEING: Amendment 39-10981. Docket 97-NM-238-AD.

Applicability: Model 737-100, -200, -300, -400, and -500 series airplanes; having forward lavatories installed; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent damage to the engines, airframe, or horizontal stabilizer, and/or to prevent a hazard to persons or property on the ground, accomplish the following:

(a) Except as provided by paragraph (c) of this AD: Within 6 months after the effective date of this AD, install a placard on the door beneath the forward lavatory sink, that warns the cabin crew not to put the selector valve for the forward lavatory water supply in the "DRAIN" position during flight. The installation shall be accomplished in accordance with Boeing Service Bulletin 737-38-1043, dated January 8, 1998.

(b) Within 36 months after the effective date of this AD, install an isolation valve in the drain line downstream of the selector valve for the forward lavatory water supply, in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Once the valve is installed, the placard described in paragraph (a) of this AD may be removed.

(c) For airplanes on which the valve installation required by paragraph (b) of this AD is accomplished within the compliance time specified in paragraph (a) of this AD, the placard installation required by paragraph (a) is not required.

(d) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

(e) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(f) The placard installation shall be done in accordance with Boeing Service Bulletin 737-38-1043, dated January 8, 1998. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(g) This amendment becomes effective on February 12, 1999.

FOR FURTHER INFORMATION CONTACT:

Don Eiford, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2788; fax (425) 227-1181.