A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to all Boeing Model 737-100, -200, -300, -400, and -500 series airplanes was published in the Federal Register on November 13, 1997 (62 FR 60810). That action proposed to 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. That action also proposed to require installation of an isolation valve in the drain line downstream of the selector valve. \n\nConsideration of Comments Received \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\nRequest to Delay Issuance of AD Pending Release of Service Information \n\n\tSeveral commenters request delay of the issuance of the AD pending the releaseof appropriate service information that provides technical details for installation of the isolation valve. The commenters state that, without such service information, they are unable to provide meaningful comments regarding the technical content of the proposed AD. \n\n\tThe FAA partially concurs with the commenter's request. The FAA recognizes that a service bulletin would provide technical details and procedures for accomplishing the actions proposed by the notice of proposed rulemaking (NPRM). However, the issue subject to public comment was the general requirement for the placard and valve installations. Further, because the valve installation is not expected to be technically complicated or difficult to accomplish, the FAA does not anticipate receiving any comments addressing the technical aspects of the valve installation. In light of this information, the FAA has determined that it is unnecessary to delay issuance of the final rule. \n\nRequest to Revise ApplicabilityOne commenter states its understanding of the applicability as being limited to those models on which forward lavatories are installed. \n\n\tThe FAA infers that the commenter is requesting that the FAA revise the applicability to include that limitation. The FAA concurs with the commenter's request, having determined that an affected airplane without a forward lavatory installed would not be subject to the identified unsafe condition. The applicability of the final rule has been revised accordingly. \n\nRequest to Consider Valve Installation as Terminating Action \n\n\tOne commenter requests that the proposed AD be revised to require installation initially of either the placard or the valve. That commenter considers the valve installation as the primary solution to address the identified unsafe condition; therefore, valve installation (if accomplished within the compliance time required for the placard installation) would preclude the need for the placard installation. That commenter suggests some airlines may choose to incorporate the valves within the 6-month window and forgo the placard installation. As further justification for its request, the commenter adds that production airplanes now include the isolation valve but not the placard. \n\n\tThe FAA concurs with the request to require installation initially of either the placard or the valve. The FAA's intent behind installation of a placard, as proposed by the NPRM, was to provide an expeditious means to achieve an acceptable level of safety pending installation of the isolation valve. However, the FAA agrees that the isolation valve is considered the primary design solution to the identified unsafe condition. Therefore, the placard would not be needed if the valve is installed within the 6-month compliance time required to install the placard. The final rule has been revised to specify this, and to indicate that installation of the valve terminates the requirement for installation of the placard.Request to Remove Requirement for Valve Installation \n\n\tOne commenter reports that it has not experienced the problem addressed in the proposed AD. The commenter states that the proposed requirement to install an isolation valve in the drain line is unnecessary, and installation of a placard should be sufficient to address the unsafe condition. \n\n\tThe FAA infers that the commenter is requesting removal of the requirement to install the valve. The FAA does not concur. The FAA has determined that long-term continued operational safety will be better assured by design changes to remove the source of the problem, rather than by reliance on the cabin crew following additional procedures. This determination, coupled with a better understanding of the human factors associated with following such procedures, has led the FAA to consider placing less emphasis on the use of informational placards and more emphasis on design improvements. The valve installation requirement is in consonance with these conditions. No change to the final rule in this regard is necessary. \n\nConcern Regarding AD Effectiveness \n\n\tOne commenter generally supports the proposal, but urges the FAA to continue to monitor occurrences of airframe damage and engine flameout due to inadvertent or erroneous drain valve activation in flight. The commenter states that the proposed corrective action would reduce but not eliminate the possibility of this unsafe condition, and urges the FAA to determine if a more active means of preventing the unsafe condition would be appropriate. \n\n\tThe FAA acknowledges the commenter's concern and will continue to monitor such occurrences of airframe damage and engine flameout. The FAA may consider further rulemaking activity if additional corrective actions are deemed necessary.\n\n Actions Since Issuance of NPRM \n\n\tSince the issuance of the NPRM, the FAA has reviewed and approved Boeing Service Bulletin 737-38-1043, dated January 8, 1998, which provides procedures for the installation of the placard. Paragraph (a) of the final rule has been revised to incorporate the service bulletin as the appropriate source of service information for the placard installation. In addition, Figure 1 of the NPRM (which depicts the placard) has been removed from the final rule because an appropriate figure is provided in the service bulletin. \n\nConclusion \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes described previously. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCost Impact\n \n\tThere are approximately 2,830 airplanes of the affected design in the worldwide fleet. The FAA estimates that 1,037 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 1 work hour per airplane toaccomplish the required placard installation, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this installation required by this AD on U.S. operators is estimated to be $62,220, or $60 per airplane. \n\n\tIt will take approximately 6 work hours per airplane to accomplish the required installation of an isolation valve, at an average labor rate of $60 per work hour. Required parts will cost approximately $300 per airplane. Based on these figures, the cost impact of this installation required by this AD on U.S. operators is estimated to be $684,420, or $660 per airplane. \n\n\tThe cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\nRegulatory Impact \n\n\tThe regulations adopted herein will not have substantial direct effects on the States, on the relationshipbetween the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \nAdoption of the Amendment \n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: PART 39 - AIRWORTHINESS DIRECTIVES \n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: