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 certain Boeing Model 737-100, -200, -300, -400, and -500 series airplanes was published as a supplemental notice of proposed rulemaking (NPRM) in the Federal Register on June 2, 1999 (64 FR 29602). That action proposed to require repetitive testing of certain main tank fuel boost pumps to identify those with degraded performance, and replacement of degraded pumps with new or serviceable pumps. That action also proposed to require eventual replacement of the existing low pressure switches for boost pumps located in the main fuel tanks with higher threshold low pressure switches, which, when accomplished, terminates the repetitive testing. \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\nRequests to Extend Compliance Time \n\n\tTwo commenters request that the proposed compliance time for replacement of the low pressure switches with higher low pressure switches be extended. \n\n\tOne commenter, the manufacturer, requests that the compliance time for installation of higher threshold switches on Model 737-200 series airplanes be extended from 2 to 3 years. The commenter states the vendor for the low pressure switches for Model 737-200 series airplanes had not committed to providing the required parts within the proposed 2-year compliance time. The commenter states that the pressure switch, unlike the one used on Model 737-300, -400, and -500 series airplanes, was previously used only on auxiliary fuel tank installations, and that production was in very low quantities. There are approximately 1,000 Model 737-200 series airplanes that would require the subject switch. The commenter also states that the vendor for the low pressure switches for Model 737-300, -400, and -500 is able to provide the needed hardware within the proposed compliance time. \n\n\tAnother commenter requests that airplanes with Argo-Tech/TRW boost pumps installed in the main tanks be allowed up to 4 years to install the higher threshold low pressure switches to accommodate parts replacement at heavy maintenance visits. \n\n\tThe FAA does not concur with the commenters' requests. In developing an appropriate compliance time for this action, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but the availability of required parts and the practical aspect of accomplishing the required replacement within an interval of time that parallels normal scheduled maintenance for the majority of affected operators. Subsequent to closure of the comment period of the proposed AD, the FAA has confirmed with the manufacturer that an ample number of required parts will be available for accomplishment of the replacement within the proposed 2-year compliance time. \n\nHowever, under the provisions of paragraph (c) of the final rule, the FAA may approve requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. \n\nRequest to Follow Service Bulletin Threshold Time \n\n\tOne commenter, an operator, recommends that the compliance time for accomplishing the pump output pressure test follow the 180-day threshold recommended in Boeing Alert Service Bulletin 737-28A1114, Revision 1, dated April 2, 1998. The commenter states that the 180-day compliance time will not compromise safe operation of the airplane fuel feed system based upon results of their testing and the redundancy associated with the fuel system on Model 737 series airplanes. \n\n\tThe FAA does not concur with the commenter's request. As discussed in the preamble of the original NPRM (63 FR 42596, August 10, 1998), the FAA has determined that an interval of 180 days would not address the identified unsafe condition in a timely manner, as degraded fuel boost pump performance may go undetected. Degraded fuel boost pump performance that is not detected by the low pressure switch and annunciated on the flight deck could result in multi-engine suction feed operation without flight crew indication, and possible consequent multiple engine failure. Redundancy in the fuel system has not prevented a number of in-service engine failures associated with pumps operating in a degraded manner. Therefore, no change to the final rule is necessary. \n\nRequest to Limit the Applicability to Certain Fuel Pumps \n\n\tOne commenter requests that the applicability of the proposed AD be revised to only affect airplanes which are fitted with General Electric Company (GEC) boost pumps. The commenter points out that the Boeing Alert Service Bulletin 737-28A1114, Revision 1, dated April 2, 1998, reveals that the unsafe condition or flameout occurred on Model 737-300, -400, and -500 seriesairplanes equipped with GEC pumps. No case of flameout was reported on Model 737-100, or -200 series airplanes equipped with Pratt and Whitney Model JT8D engines. The commenter states that its request will in no way affect the safety of the airplane. \n\n\tThe FAA does not concur with the commenter's request. As discussed in the supplemental NPRM, the FAA has determined that all pump configurations on affected Boeing Model 737 series airplanes may be subject to the identified unsafe condition. \n\nExplanation of Changes to Proposal \n\n\tThe FAA has revised paragraph (a)(4) of the final rule to clarify that accomplishment of the required replacement constitutes terminating action for paragraphs (a)(1), (a)(2), and (a)(3) of this AD. \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 change previously described. The FAA has determined that this change will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCost Impact \n\n\tThere are approximately 2,772 airplanes of the affected design in the worldwide fleet. The FAA estimates that 1,140 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 2-8 work hours per airplane to accomplish the required testing for airplanes equipped with GEC pumps, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the testing required by this AD on U.S. operators is estimated to be $120-$480 per airplane, per testing cycle. \n\n\tIt will take approximately 4-6 work hours per airplane to accomplish the required modification, at an average labor rate of $60 per work hour. Required parts will cost $1,900 (for airplanes equipped with part number (P/N) 60B92400-3 low pressure switches) or $2,700 (for airplanes equipped with P/N 10-3067-3 low pressure switches). Based on these figures, the cost impact of the modification required by this AD on U.S. operators is estimated to be $273,600-$410,400, or $2,140-$3,060 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 relationship between 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 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\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: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. \n§ 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: