Discussion \n\n\tWe received three reports of cracks in the fuselage skin common to stringer S-1 and between station (STA) 400 and STA 460. In all three cases, there were cracks in adjacent 10-inch tear strap bays. In one case, there were cracks in four adjacent 10-inch tear strap bays. The cracks measured between 4.0 and 10.5 inches long. The airplanes had accumulated between 42,038 and 57,523 total flight cycles. Analysis indicates that the cracks were caused by fatigue due to high tension stresses and local bending at the edge of the chem-mill pockets of the bonded fuselage skin. Airplanes with 20-inch tear strap bays are also susceptible to cracks at this location. Fatigue cracking of the fuselage skin panels at the chem-mill steps, if not detected and corrected, could result in sudden fracture and failure of the fuselage skin panels, and consequent rapid decompression of the airplane. \n\nRelevant Service Information \n\n\tWe reviewed Boeing Alert Service Bulletin 737-53A1293, dated August 13, 2008. The service bulletin describes procedures for repetitive external detailed inspections or non-destructive inspections (NDI) to detect cracks in the fuselage skin along the chem-mill steps at stringers S-1 and S-2R between STA 400 and STA 460, and contacting Boeing for repair instructions. The NDI inspections that can be used are medium frequency eddy current, magneto optical imaging, or c-scan. For the initial inspection, the service bulletin specifies a compliance time of before 35,000 total flight cycles, or within 500 flight cycles after the date on the service bulletin, whichever occurs later. For the repetitive inspections, the service bulletin specifies repeat intervals ranging between 1,200 and 4,500 flight cycles, depending on the airplane configuration and the type of inspection previously done. \n\nFAA's Determination and Requirements of This AD \n\n\tWe are issuing this AD because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the(se) same type design(s). This AD requires accomplishing the actions specified in the service information described previously, except as discussed under "Difference Between the AD and the Service Information.'' \n\nDifference Between the AD and the Service Information \n\n\tBoeing Alert Service Bulletin 737-53A1293, dated August 13, 2008, specifies contacting the manufacturer for instructions on how to repair a certain condition, but this AD requires repairing that condition in one of the following ways: \n\tUsing a method that we approve; or \n\tUsing data that meet the certification basis of the airplane, and that have been approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization whom we have authorized to make those findings. \n\nInterim Action \n\n\tWe consider this AD interim action. If final action is later identified, we might consider further rulemaking then. \n\nFAA's Justification and Determination of the Effective Date \n\n\tWe are issuing this AD to detect and correct fatigue cracking of the fuselage skin panels at the chem-mill steps, which could result in sudden fracture and failure of the fuselage skin panels, and consequent rapid decompression of the airplane. Because of our requirement to promote safe flight of civil aircraft and thus, the critical need to assure the structural integrity of the fuselage and the short compliance time involved with this action, this AD must be issued immediately. \n\tBecause an unsafe condition exists that requires the immediate adoption of this AD, we find that notice and opportunity for prior public comment hereon are impracticable and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tThis AD is a final rule that involves requirements affecting flight safety, and we did not provide you with noticeand an opportunity to provide your comments before it becomes effective. However, we invite you to send any written data, views, or arguments about this AD. Send your comments to an address listed under the ADDRESSES section. Include "Docket No. FAA-2008-0947; Directorate Identifier 2008-NM-154-AD'' at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this AD. We will consider all comments received by the closing date and may amend this AD because of those comments. \n\tWe will post all comments we receive, without change, to http:// www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this AD. \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\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\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\t(2) Is not a "significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), and \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\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 amendsSec. 39.13 by adding the following new AD: