Discussion \n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. That NPRM was published in the Federal Register on July 6, 2007 (72 FR 36907). That NPRM proposed to require revising the FAA- approved maintenance program to incorporate new airworthiness limitations (AWLs) for fuel tank systems to satisfy Special Federal Aviation Regulation No. 88 requirements. That NPRM also proposed to require the initial inspection of a certain repetitive AWL inspection to phase in that inspection, and repair if necessary. \n\nActions Since NPRM Was Issued \n\n\tSince we issued the NPRM, Boeing has issued Revision March 2008 of the 737-100/200/200C/300/400/500 Airworthiness Limitations (AWLs) and Certification Maintenance Requirements (CMRs), D6-38278-CMR (hereafter referred to as "Revision March 2008 of Document D6-38278-CMR"). The NPRM referred to Revision May 2006 of Document D6-38278-CMR as the appropriate source of service information for accomplishing the proposed actions. Revision March 2008 of Document D6-38278-CMR, among other actions, includes the following changes: \n\n\tRemoves the repetitive task interval of 36,000 flight cycles from AWLs No. 28-AWL-01 and No. 28-AWL-03. \n\n\tRevises the task description for AWL No. 28-AWL-01 to harmonize it with AWL No. 28-AWL-02 by removing references to certain station numbers. \n\n\tRevises AWL No. 28-AWL-03 to reflect the new maximum loop resistance values associated with the lightning protection of the unpressurized fuel quantity indicating system (FQIS) wire bundle installations. \n\n\tAccordingly, we have revised paragraphs (f), (g), and (h) of this AD to refer to Revision March 2008 of Document D6-38278-CMR. We also have added a new paragraph (j) to this AD specifying that actions done before the effective date of this AD in accordance with Revisions May 2006 through November 2007 of Document D6-38278-CMR are acceptable for compliance with the corresponding requirements of paragraphs (g) and (h) of this AD. \n\n\tWe also have removed reference to 36,000 total flight hours from paragraph (h)(1) of this AD and revised the initial threshold for accomplishing AWL No. 28-AWL-03 to within 120 months since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness. \n\n\tOperators should note that paragraph (g) of this AD requires only incorporating AWLs No. 28-AWL-01 through No. 28-AWL-20 inclusive for Model 737-100, -200, and -200C series airplanes, and AWLs No. 28-AWL-01 through No. 28-AWL-19 inclusive for Model 737-300, -400, and -500 series airplanes. Revision September 2006 of Document D6-38278-CMR added AWL inspections of the fuel boost pump auto shutoff system for the center and auxiliary fuel tanks (specified as AWLs No. 28-AWL-20and No. 28-AWL-21 for Model 737-300, -400, and -500 series airplanes, and AWLs No. 28- AWL-21 and No. 28-AWL-22 for Model 737-100, -200, and -200C series airplanes). Revision November 2007 of Document D6-38278-CMR added an AWL inspection of the boost pump ground fault interrupter (specified as AWL No. 28-AWL-22 for Model 737-300, -400, and -500 series airplanes, and AWL No. 28-AWL-23 for Model 737-100, -200, and -200C series airplanes). We might issue additional rulemaking to require the incorporation of those AWLs. However, as an optional action, operators may incorporate those AWLs as specified in paragraph (g) of this AD. \n\nOther Changes Made to This AD \n\n\tFor standardization purposes, we have revised this AD in the following ways: \n\n\tWe have added a new paragraph (i) to this AD to specify that no alternative inspections, inspection intervals, or critical design configuration control limitations (CDCCLs) may be used unless they are part of a later approved revision of Revision March 2008 of Document D6-38278-CMR, or unless they are approved as an alternative method of compliance (AMOC). Inclusion of this paragraph in the AD is intended to ensure that the AD-mandated airworthiness limitations changes are treated the same as the airworthiness limitations issued with the original type certificate. \n\n\tWe have revised Note 1 of this AD to clarify that an operator must request approval for an AMOC if the operator cannot accomplish the required inspections because an airplane has been previously modified, altered, or repaired in the areas addressed by the required inspections. \n\n\tWe have revised paragraph (h) of this AD to specify that accomplishing AWL No. 28-AWL-03 as part of an FAA-approved maintenance program before the applicable compliance time constitutes compliance with the applicable requirements of that paragraph. \n\n\tWe have deleted Appendix 1 and Appendix 2 from this AD, since Revision March 2008 of Document D6-38278-CMR already contains most ofthe updated information that is listed in those appendices of the NPRM. \n\nComments \n\n\tWe gave the public the opportunity to participate in developing this AD. We considered the comments received from the five commenters. \n\nRequest To Revise the Loop Resistance Values for AWL No. 28-AWL-03 \n\n\tBoeing, KLM Royal Dutch Airlines (KLM), and Lufthansa state that the loop resistance values for AWL No. 28-AWL-03 specified in Revision May 2006 of Document D6-38278-CMR are going to be revised, since those values are relevant for production airplanes. The commenters also state that the revised values will be more representative of the expected values for in-service airplanes. Boeing points out that, according to paragraph (h) of the NPRM, the revised values should be able to be used in accordance with a later revision of the CMR if the revision is approved by the Seattle Aircraft Certification Office (ACO), FAA. \n\n\tWe agree that operators may use the revised loop resistance values for AWL No. 28-AWL-03 in accordance with Revision March 2008 of Document D6-38278-CMR. As stated previously, we have revised this AD accordingly. \n\nRequest To Revise Intervals for Certain AWL Inspections \n\n\tKLM, on behalf of several operators, requests that we review a 45- page proposal to align certain airworthiness limitation item (ALI) intervals with the applicable maintenance significant item (MSI) and enhanced zonal analysis procedure (EZAP) intervals for Model 737, 747, 757, 767, and 777 airplanes. The recommendations in that proposal ensure that the ALI intervals align with the maintenance schedules of the operators. Among other changes, the proposal recommends extending certain AWL inspection intervals from 10 years/36,000 flight cycles to 12 years for Model 737-100, -200, -300, -400, and -500 series airplanes. \n\n\tLufthansa and the Air Transport Association (ATA), on behalf of its member U.S. Airways, both note an inconsistency between the inspection interval specified in Revision May 2006 of Document D6-38278-CMR and the compliance threshold specified in paragraph (h)(1) of the NPRM. The NPRM specifies accomplishing the initial inspection within 36,000 total flight hours or 120 months since the date of issuance of the original standard airworthiness certificate or the date of issuance of the original export certificate of airworthiness, whichever occurs first. However, Revision May 2006 of Document D6-38278-CMR specifies a repetitive interval of 36,000 total flight cycles or 120 months, whichever occurs first. U.S. Airways requests we verify whether the initial inspection interval should be in units of flight cycles or flight hours. \n\n\tWe disagree with KLM's request to extend certain AWL inspection intervals to 12 years. However, as stated previously, we have deleted the 36,000-total-flight-hour parameter from paragraph (h)(1) of this AD to correspond with the task interval for AWL No. 28-AWL-03 as specified in Revision March 2008 of Document D6-38278-CMR. In developing an appropriate compliance time for this action, we considered the urgency associated with the subject unsafe condition and the practical aspect of accomplishing the required actions within a period of time that corresponds to the normal scheduled maintenance for most affected operators. However, according to the provisions of paragraph (k) of this AD, we might approve requests to adjust the compliance time if the request includes data that prove that the new compliance time would provide an acceptable level of safety. \n\nRequest To Revise Note 1 \n\n\tBoeing requests that we revise Note 1 of the NPRM to clarify the need for an AMOC. Boeing states that the current wording is difficult to follow, and that the note is meant to inform operators that an AMOC to the required AWLs might be required if an operator has previously modified, altered, or repaired the areas addressed by the limitations. Boeing requests that we revise Note 1 as follows: \n\n\tAdd the words "accordingto paragraph (g)" at the end of the first sentence. \n\n\tReplace the words "revision to" with "deviation from" in the last sentence. \n\n\tDelete the words "(g) or" and "as applicable" from the last sentence. \n\n\tAs stated previously, we have clarified the language in Note 1 of this AD for standardization with other similar ADs. The language the commenter requests that we change does not appear in the revised note. Therefore, no additional change to this AD is necessary in this regard. \n\nRequest To Extend the Grace Period for AWL No. 28-AWL-03 \n\n\tKLM expects to have problems accomplishing the initial inspection of AWL No. 28-AWL-03 within the 24-month grace period. The commenter states that if it does the check and does not reach the specified values, then tank entry outside of heavy maintenance would be necessary. The commenter also states that it would be helpful to plan to do this inspection during an overhaul. \n\n\tWe infer that KLM requests that we extend the grace period forAWL No. 28-AWL-03 in paragraph (h) of this AD to allow accomplishing the initial inspection during a regularly scheduled "D" check (about 6 years). We disagree with extending the grace period to 6 years. In developing an appropriate compliance time for this action, we considered the safety implications, the rate of lightning strikes in the fleet, and the average age of the fleet. In consideration of these items, we have determined that an initial compliance time of 120 months (as discussed previously) with a grace period of 24 months will ensure an acceptable level of safety. We have not changed the grace period for AWL No. 28-AWL-03 in this regard. \n\nRequest To Add Applicability to Paragraph (g) \n\n\tLufthansa states that the applicability of the AWL tasks should be included in the AWL table of the AD. \n\tWe infer the commenter requests that we include the applicability for AWL No. 28-AWL-03 in paragraph (g) of this AD. (The commenter made the same request for a similar NPRM, whichcontained an "AWL table.") We agree to add the airplane applicability to paragraph (g) of this AD because AWL No. 28-AWL-03 only applies to airplanes on which certain design changes have been incorporated. We have revised paragraph (g) of this AD accordingly. \n\nRequest To Clarify Need for AMOCs \n\n\tThe ATA, on behalf of its member U.S. Airways, requests that we clarify whether operators must obtain AMOCs for AWLs that are not applicable to their airplanes. U.S. Airways also requests that we clarify that some of the items identified in Appendix 2 of the NPRM might not be applicable to all Model 737-300, -400, and -500 series airplanes. U.S. Airways states that it will not be able to comply with certain AWL inspections or CDCCLs because it has not incorporated the relevant service bulletins identified in Revision May 2006 of Document D6-38278-CMR on several of its airplanes. \n\n\tDocument D6-38278-CMR contains an applicability column that identifies the airplane configuration to whichthe AWL applies. The AWL is required only for those airplanes that have that configuration. If the applicability column identifies a service bulletin, then the operator would not need to adhere to the AWL until the airplane is modified in accordance with that service bulletin. There is no need to obtain an AMOC for airplanes that have not been modified. We agree that some of the items identified in Appendix 2 of the NPRM might not be applicable to all Model 737-300, -400, and -500 series airplanes. However, no change to this AD is necessary in this regard, since we have deleted Appendix 2 from this AD. \n\nRequest To Clarify if Latest Revision of Document D6-38278-CMR is Required \n\n\tThe ATA, on behalf of its member U.S. Airways, requests that we clarify whether the latest revision of Document D6-38278-CMR will be incorporated into the final rule. The commenters note that Boeing has published a later revision of Document D6-38278-CMR than the one referenced in the NPRM. \n\n\tWe haverevised this AD to refer to the latest revision of Document D6-38278-CMR because paragraphs (g) and (h) of this AD allow the use of later approved revisions of that document. That document has been revised since then to include additional AWLs associated with the incorporation of certain design changes. As stated previously, we might require those design changes and associated AWLs with separate rulemaking actions, but operators may choose to incorporate the new AWLs before then. \n\nRequest To Clarify Revision Date of Document D6-38278-CMR \n\n\tThe ATA, on behalf of its member U.S. Airways, notes that the "Changes to Fuel Tank System AWLs" and "Exceptional Short-Term Extensions" sections of the NPRM refer to Revision March 2006 of Document D6-38278-CMR. U.S. Airways believes that the correct revision date should be May 2006 to match the rest of the NPRM. \n\n\tWe infer the commenters request that we change the revision date to May 2006. We agree that the NPRM should have referred to Revision May 2006 of Document D6-38278-CMR because that revision, and other later approved revisions, are the subject of this AD. Revision March 2006 of Document D6-38278-CMR was originally included in the NPRM because the AWLs for fuel tank systems were first incorporated in that document. However, we have not changed this AD since the paragraphs that the commenters refer to are not retained in the final rule. \n\nConclusion \n\n\tWe reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting the AD with the changes described previously. We also determined that these changes will not increase the economic burden on any operator or increase the scope of the AD. \n\nCosts of Compliance \n\n\tThere are about 2,337 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs, at an average labor rate of $80 per work hour, for U.S. operators to comply with this AD. \n\n\t\t\t\tEstimated Costs\n\n\nAction\nWork hours\nParts\nCost per airplane\nNumber of U.S.-registered airplanes\nFleet cost\nMaintenance program revision\n8\nNone\n$640\n672\n$430,080\nInspection\n8\nNone\n$640\n672\n$430,080\n\n\nAuthority for This Rulemaking \n\n\tTitle 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. "Subtitle VII: Aviation Programs," describes in more detail the scope of the Agency's authority. \n\n\tWe are issuing this rulemaking under the authority described in "Subtitle VII, Part A, Subpart III, Section 44701: General requirements." Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. \n\nRegulatory Findings \n\n\tThis AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect 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. \n\n\tFor the reasons discussed above, I certify that this AD: \n\n\t(1) Is not a "significant regulatory action" under Executive Order 12866, \n\n\t(2) Is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), and \n\n\t(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. \n\n\tYou can find our regulatory evaluation and the estimated costs of compliance in the AD Docket. \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\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n2. The FAA amends Sec. 39.13 by adding the following new AD: