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 certain Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. That NPRM was published in the Federal Register on July 6, 2007 (72 FR 36920). That NPRM proposed to require revising the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness (ICA) by incorporating new limitations 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 Temporary Revision (TR) 09-020, dated March 2008. Boeing TR 09-020 is published as Section 9 of the Boeing 737-600/700/800/900 Maintenance Planning Data (MPD) Document, D626A001-CMR, Revision March 2008 (hereafter referred to as "Revision March 2008 of the MPD"). The NPRM referred to Revision March 2006 of the MPD as the appropriate source of service information for accomplishing the proposed actions. Revision March 2008 of the MPD, 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 the MPD. 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 March 2006 through February 2008 of the MPD are acceptable for compliance with the corresponding requirements of paragraphs (g) and (h) of this AD. (In Revision March 2007 of the MPD, Boeing revised the document title to "737-600/700/800/900.") \n\n\tWe also have removed reference to 36,000 total flight cycles 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\tSince publication of Revision March 2006 of the MPD, Boeing has revised the contents of certain subsections of the MPD. Information pertaining to the fuel system AWLs has been removed from Subsection D, "AIRWORTHINESS LIMITATIONS--SYSTEMS" and placed into a new Subsection E, "AIRWORTHINESS LIMITATIONS--FUEL SYSTEMS." The subsequent subsections of the MPD were reidentified accordingly. Therefore, we have revised paragraphs (g)(1), (g)(2), and (g)(3) of this AD to refer to Subsections E, F, and G, respectively. \n\n\tOperators should note that we have revised paragraph (g) of this AD to require incorporating only AWLs No. 28-AWL-01 through No. 28-AWL-22 inclusive. AWL No. 28-AWL-23 was added in Revision May 2006 of the MPD, and AWL No. 28-AWL-24 was added in Revision October 2006 of the MPD. However, as an optional action, operators may incorporate those two AWLs as specified in paragraph (g) of this AD. \n\n\tOperators should also note that we have issued a separate NPRM (Docket No. FAA-2007-28661) that, in part, proposes to incorporate AWLs No. 28-AWL-19 and No. 28-AWL-23 into the AWLs section of the ICA. That NPRM was published in the Federal Register on July 10, 2007 (72 FR 37479). \n\n\tWe have also issued AD 2008-06-03, amendment 39-15415 (73 FR 13081, March 12, 2008) that, in part, requires revising the AWLs section of the ICA to incorporate AWLs No. 28-AWL-21, No. 28-AWL-22, and No. 28- AWL-24. Therefore, we have added a new paragraph (k) to this AD specifying that incorporating AWLs No. 28-AWL-21, No. 28-AWL-22, and No. 28-AWL-24 in accordance with paragraph (g) of this AD terminates the action required by paragraph (h)(1) of AD 2008-06-03. \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 the MPD, 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.We have revised Note 2 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\nComments \n\n\tWe gave the public the opportunity to participate in developing this AD. We considered the comments received from the six commenters. \n\nRequest To Revise the Loop Resistance Values for AWL No. 28-AWL-03 \n\n\tBoeing and KLM Royal Dutch Airlines (KLM) state that the loop resistance values for AWL No. 28-AWL-03 specified in Revision March 2006 of the MPD 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 MPD 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 the MPD. As stated previously, we have revised this AD accordingly. \n\nRequest To Extend the Task 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 737-600, -700, -700C, -800, and -900 series airplanes. \n\n\tThe Air Transport Association (ATA), on behalf of its member Delta Airlines (DAL), notes an inconsistency between the inspection interval specified in Revision March 2006 of the MPD and the compliance threshold specified in paragraph (h)(1) of the NPRM. Paragraph (h)(1) of the NPRM specifies accomplishing the initial inspection prior to the accumulation of 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. DAL requests that we revise the compliance threshold to 36,000 "total flight cycles." \n\n\tWe disagree with KLM's request to extend certain AWL inspectionintervals 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 the MPD. 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 (l) 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 Require the Incorporation of AWL No. 28-AWL-24 \n\n\tThe ATA, on behalf of its member Delta Airlines (DAL), notes that AD 2008-06-03 requires a revision to the AWLs section of the Instructions for Continued Airworthiness to incorporate AWLs No. 28- AWL-21, No. 28-AWL-22, and No. 28-AWL-24. DAL states that AD 2008-06-03 appears to duplicate the proposed requirements of the NPRM, and that it is more appropriate to have this AD require the incorporation of AWLs No. 28-AWL-21, No. 28-AWL-22, and No. 28-AWL-24. \n\n\tWe infer that the commenters request that we delete paragraph (h)(1) from AD 2008-06-03, and revise this AD to require incorporating AWL No. 28-AWL-24 into the AWLs section of the Instructions for Continued Airworthiness. (This AD requires the incorporation of AWLs No. 28-AWL-01 through No 28-AWL-22 and specifies that AWL No. 28-AWL-24 may be incorporated as an optional action.) We do not agree to revise this AD or AD 2008-06-03. Revision March 2008 of the MPD contains an applicability column that identifies the airplane configuration to which the AWL applies. That AWL is required only for 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 penalty for incorporating the AWL before accomplishing the actions specified in the service bulletin, and doing so actually reduces the paperwork burden for the FAA and the operators by incorporating subsections E, F, and G in their entirety. \n\n\tAlso, it is necessary to have AD 2008-06-03 require the incorporation of AWLs No 28-AWL-21, No. 28-AWL-22, and No. 28-AWL-24, since those AWLs are tied to the design change required by paragraph (g) of AD 2008-06-03. If an operator were to comply with AD 2008-06-03 before complying with this AD and did not revise its MPD concurrently with accomplishing the design change, then the operations checks required by those AWLs would not be performed at the proper time. \n\n\tHowever, we do not intend for operators to incorporate AWLs No. 28- AWL-21 and No. 28-AWL-22 into the AWLs section of the Instructions for Continued Airworthiness twice by two separate airworthiness directives. As stated previously, we have added a new paragraph (k) to this AD specifying that incorporating AWLs No. 28-AWL-21, No. 28-AWL-22, and No. 28-AWL-24 in accordance with paragraph (g) of this AD terminates the action required by paragraph (h)(1) of AD 2008-06-03. \n\nRequest To Issue Separate Airworthiness Directives \n\n\tThe ATA, on behalf of its member American Airlines (AAL), requests that we delete the initial inspection and repair specified in paragraph (h) of the NPRM and address those actions with a separate airworthiness directive. AAL states that the different actions and compliance times proposed in paragraphs (g) and (h) of the NPRM create confusion and difficulty in tracking compliance. AAL also states that it will not be able to say it is fully compliant with the requirements of the NPRM by December 16, 2008, because it will still be in the process of completing the initial inspection and repair specified in paragraph (h) of the NPRM. \n\n\tAirTran Airways states that it is unclear as to why AWL No. 28-AWL- 03 is given special consideration in paragraph (h) of the NPRM. AirTran Airways also states that, although it is not affected by the compliance time specified in paragraph (h)(2) of the NPRM, it assumes that there are other operators who will be affected by it due to the age of the fleet. AirTran Airways, therefore, requests that we substantiate why the NPRM contains a more restrictive requirement for AWL No. 28-AWL-03. \n\n\tWe disagree with issuing a separate airworthiness directive to address the requirements of the paragraph (h) of this AD. Some airplanes might have already passed the age when the initial inspection required by AWL No. 28-AWL-03 should have been accomplished. The intent of paragraph (h) of this AD is to phase in that inspection for those airplanes. Further, paragraph (h)(2) of this AD provides a 24-month grace period for an airplane that has alreadyexceeded the compliance threshold specified in paragraph (h)(1) of this AD. No change to this AD is necessary in this regard. \n\nRequest To Revise Appendix 1 \n\n\tBoeing requests that we revise Appendix 1 of the NPRM to add an additional ATA section for AWL No. 28-AWL-02 and for AWL No. 28-AWL-17. The ATA, on behalf of its member DAL, requests that we revise Appendix 1 of the NPRM as follows: (1) add the task title for AWLs No. 28-AWL- 08, No. 28-AWL-12, No. 28-AWL-13, and No. 28-AWL-22 based on the information found in the MPD, (2) add the "ALI/CDCCL" designation, airplane maintenance manual (AMM) reference, and task title for AWL No. 28-AWL-20 based on the information in the MPD, and (3) delete any duplicate sources of service information and reference a single source document that provides the task instructions necessary to comply with the AWLs. \n\n\tWe disagree with revising the AMM references, since we have deleted Appendix 1 from this AD. The purpose of Appendix 1 was to assistoperators in identifying the AMM tasks that could affect compliance with a CDCCL. However, we have also received several similar comments regarding the appendices in other NPRMs that address the same unsafe condition on other Boeing airplanes. Those comments indicate that including non-required information in those NPRMs has caused confusion. Further, Revision March 2008 of the MPD contains most of the updated information that is listed in Appendix 1 of the NPRM. Therefore, we have removed Appendix 1 from this AD. \n\nRequest To Revise Note 2 \n\n\tBoeing requests that we revise Note 2 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 MPD 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 2 as follows: \n\n\tAdd the words "according to 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 2 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 for AWL No. 28-AWL-03 in paragraph (h)(2) 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 Revise the Estimated Costs Table \n\n\tThe ATA, on behalf of its member DAL, states that it disagrees with the cost estimate for accomplishing the inspection provided in the "Estimated Costs" table of the NPRM because it does not include the time required for accomplishing the additional repetitive inspections. DAL also states that it willtake much more than eight hours to accomplish the initial inspection. \n\n\tWe infer the commenters request that we revise the "Estimated Cost" table in this AD to reflect the cost of accomplishing the repetitive inspections. We do not agree because the repetitive inspections are not directly required by this AD. This AD only requires the change to the maintenance program via a revision to the MPD, and the initial accomplishment of AWL No. 28-AWL-03. Section 91.403(c) of the Federal Aviation Regulations (14 CFR part 91.403(c)) requires the repetitive inspections once the maintenance program is changed. Although DAL states the initial inspection takes more than 8 hours, it has not provided an estimate. Therefore, we have not changed this AD in this regard. \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 1,960 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\tEstimated Costs \n\n\nAction\nWork hours\nParts\nCost per airplane\nNumber of U.S.-registered airplanes\nFleet cost\nAWLs revision\n8\nNone\n$640\n682\n$436,480\nInspection\n8\nNone\n$640\n682\n$436,480\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: