Examining the Docket \n\n\n\tYou may examine the airworthiness directive (AD) docket on the Internet at http://dms.dot.gov or in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647-5227) is located on the plaza level of the Nassif Building at the street address stated in the ADDRESSES section. \n\nDiscussion \n\n\tThe FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an AD that would apply to all Boeing Model 737- 600, -700, -700C, -800, and -900 series airplanes. That NPRM was published in the Federal Register on May 2, 2005 (70 FR 22620). That NPRM proposed to require repetitive inspections of the aft pressure bulkhead web for fatigue cracks, crack indications, discrepant holes, and corrosion; and repair if necessary. \n\nComments \n\n\tWe provided the public the opportunity to participate in the development of this AD. We have considered the comments received. \n\nSupportive Comments \n\n\tTwo commenters, including the manufacturer, support the proposed AD. \n\nRequest To Add Provision for Special Flight Permits \n\n\tOne commenter requests that the proposed AD be revised to include a phrase used in earlier ADs to permit the use of special flight permits. The commenter explains that, due to the number of work hours needed to gain access to the forward side of the aft pressure bulkhead, it needs to use the provisions for special flight permits. We infer that the commenter believes that because the proposed AD does not contain information on ferry flights, ferry flights are not allowed. \n\n\tWe do not agree with the commenter's request to add the special flight permit language, nor do we agree with the commenter's inference that special flight permits are not allowed by this AD. Special flight permits are allowed unless limitations or prohibitions are specifically identified inthe AD. For this AD there are no limitations or prohibitions. On July 10, 2002, we issued a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs the FAA's airworthiness directives system. The regulation now includes material that relates to altered products, special flight permits (i.e., ferry flights), and alternative methods of compliance (AMOCs). Since we have now included this information in 14 CFR part 39, information on special flight permits is not included in each individual AD unless there are limitations on special flight permits for an individual AD. We have not changed the AD in this regard. \n\nRequest To Add Language That Advises Operators How To Address Pre- existing Repairs \n\n\tAnother commenter requests that the proposed AD be revised to include language advising operators how to treat pre-existing repairs in the inspection area of the aft pressure bulkhead. The commenter justifies the request by noting that the "* * * bulkhead is the subject ofnumerous other service bulletins and other ADs, any or all of which may have resulted in the installation of repairs in the inspection area," and that the absence of such advisory language would require AMOCs for each instance of pre-existing repairs. We infer that the commenter believes that the AD requires AMOCs for each pre-existing repair that prevents someone from complying with the requirements of the AD, and is requesting that the AD include specific language to provide relief for treating these pre-existing repairs. \n\n\tWe understand the commenter's concern about obtaining AMOCs for pre-existing repairs, especially since there are three ADs that cover the inspection area. We concur with the commenter in this regard. As noted in the reply to the previous comment on special flight permits, we issued a new version of 14 CFR part 39 on July 10, 2002. In section 39.17, it states, "If a change in a product affects your ability to accomplish the actions required by the airworthinessdirective in any way, you must request FAA approval of an alternative method of compliance." This statement means that pre-existing repairs do not require AMOC approval unless they affect the operator's ability to accomplish the actions of the AD. Since we cannot anticipate the wide variety of possible repair configurations, this is best handled by requesting an AMOC for each repair. We have not changed the AD in this regard. \n\nRequest To Query Boeing for Availability of Parts \n\n\tOne commenter notes that certain repairs would require replacement of sections of curved structural members that are difficult for operators to fabricate on short notice. The commenter suggests that Boeing should be queried for availability of replacement materials in the event that an inspection finds the need for corrective action. \n\n\tWe agree that certain parts may be difficult for operators to fabricate on short notice (i.e., before further flight). We contacted Boeing about parts availability in regard to this AD, and have confirmed that a sufficient quantity of parts is available. We encourage operators to contact Boeing for specific information on parts availability. We have not changed the AD in this regard. \n\nRequest to Operator for Additional Repair Guidance \n\n\tOne commenter requests that Boeing provide additional repair guidance other than "contact Boeing." The commenter notes that the manufacturer has previous experience in addressing similar repairs in the area to be inspected in accordance with this AD. The commenter acknowledges that every repair is different, but believes that a repair drawing or structural-repair-manual-type of repair should be made available. The commenter also states that it is impractical to contact Boeing in an airline's operational environment. \n\n\tWe acknowledge the commenter's request. We understand that general repair information applicable to this AD would help operators plan for any potential corrective action. We have coordinated thisissue with Boeing. However, in this particular area, it is difficult to develop specific guidelines for the various conditions that an operator may encounter. Although no general repair information exists now (at time of publication), we remind operators that we may approve (if submitted and approved) repair drawings as allowed for in paragraph (i) of this AD, which describes ways to get approval of an alternative method of compliance (AMOC). We remind operators that they may apply for an AMOC in accordance with the provisions in paragraphs (i) and (g) of this AD. We have not changed the AD in this regard. \n\nConclusion \n\n\tWe have carefully reviewed the available data, including the comments received, and determined that air safety and the public interest require adopting the AD as proposed. \n\nExplanation of Change Made to This AD \n\n\tWe have simplified paragraph (g) of this AD by referring to the "Alternative Methods of Compliance (AMOCs)" paragraph of this AD for repair methods. \n\nClarification of Alternative Method of Compliance (AMOC) Paragraph \n\n\tWe have revised this AD to clarify the appropriate procedure for notifying the principal inspector before using any approved AMOC on any airplane to which the AMOC applies. \n\nCosts of Compliance \n\n\tThere are about 978 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs for U.S. operators to comply with this AD: \n\n\tEstimated Costs \n\n\nAction \nWork hours \nAverage labor rate per hour \nParts \nCost per airplane \nNumber of U.S.-\nregistered airplanes \nFleet cost \n\n\n\n\n\n\n\nLFEC and detailed inspection, per inspection cycle. \n8 \n$65 \nNone \n$520 per inspection cycle \n630 \n$327,600 per inspection cycle. \n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nHFEC and detailed inspection (in lieu of LFEC and detailed inspection), per inspection cycle. \n2 \n65 \nNone \n$130 per inspection cycle \n630\n$81,900 per inspection cycle. \n\nAuthority for ThisRulemaking \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\tWe have determined that this 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\tWe prepared a regulatory evaluation of the estimated costs to comply with this AD and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation. \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 Federal Aviation Administration (FAA) amends Sec. 39.13 by adding the following new airworthiness directive (AD):