Discussion \n\n\tWe have received reports of cracks found in the horizontal stabilizer--in the upper and lower aft skin panels at the aft inboard corner at station XH = 8.2, and in the rear spar upper caps adjacent to the aft skin panel at station XH = 10.0. These cracks were found during maintenance visual inspections. \n\n\tThe cause of the cracking is still under investigation. If not corrected, the cracked upper and lower aft skin panels and rear spar upper caps could lead to the loss of overall structural integrity of the horizontal stabilizer. \n\nRelevant Service Information \n\n\tWe have reviewed Boeing Alert Service Bulletin MD80-55A065, dated April 25, 2007. The service bulletin describes procedures for repetitive low- and high-frequency eddy current inspections to detect cracks of the horizontal stabilizer's upper and lower aft skin panels and rear spar upper caps. The service bulletin provides options for corrective action based on crack length,location, and repairability; these options include some combination of the following actions: \n\n\tStop drilling the end of the crack; \n\n\tTrimming the crack and installing a filler; \n\n\tInstalling a skin panel splice or rear spar upper cap splice; \n\n\tReplacing the skin panel or rear spar upper cap with a new part; and \n\n\tRepeating the inspection of the cracked area (including aft skin panels, skin panel splice, and rear spar upper cap). \n\n\tThe repetitive inspection intervals, which range from 200 to 2,600 flight cycles, depend on the option used. \n\n\tAccomplishing the actions specified in the service information is intended to adequately address the unsafe condition. \n\nFAA's Determination and Requirements of This AD \n\n\tThe unsafe condition described previously is likely to exist or develop on other airplanes of the same type design. For this reason, we are issuing this AD to detect and correct cracks in the upper and lower aft skin panels and rear spar upper caps, which,if not corrected, could lead to the loss of overall structural integrity of the horizontal stabilizer. This AD requires accomplishing the actions specified in the service information described previously, except as discussed under "Differences Between the AD and the Service Bulletin'' below. \n\nDifferences Between the AD and the Service Bulletin \n\n\tThe service bulletin specifies that any splice installed as part of a crack repair option be inspected within 20,000 flight cycles after the repair. But the service bulletin notes that the type, method, and repetitive interval for this inspection will be identified by Boeing at a later date. (See paragraph 1.E., note (a) of Tables 1 and 2 of the service bulletin.) To ensure continued safety, we have determined that this inspection and its repetitive interval must be adequately defined. Therefore, this AD requires that the inspection type, method, and repetitive interval be approved either by the FAA, or in accordance with 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\n\tFor a crack that meets the Condition 2 criteria specified in Table 1 or Table 3 in paragraph 1.E. of the service bulletin, Options 1 and 2 specify temporary repairs followed by repetitive inspections of the area, but provide no terminating action for these repetitive inspections. In this case, this AD requires, within 4,000 flight cycles after the crack is detected, either installing a horizontal stabilizer aft skin panel splice or removing and replacing the horizontal stabilizer aft skin panel, in accordance with Option 3 or 4 of the applicable table, followed by the applicable repetitive inspections specified in Option 3 or 4. We have determined that this action is necessary to maintain the safety of the fleet. \n\n\tWe have coordinated these differences with Boeing. \n\nFAA's Determination of the Effective Date \n\n\tSince an unsafe condition exists that requires the immediate adoption of this AD, we have found that notice and opportunity for public comment before issuing this AD are impracticable, and that good cause exists to make this AD effective in less than 30 days. \n\nComments Invited \n\n\tThis AD is a final rule that involves requirements that affect flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any relevant written data, views, or arguments regarding this AD. Send your comments to an address listed in the ADDRESSES section. Include "Docket No. FAA-2007- 28100; Directorate Identifier 2007-NM-103-AD'' at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD that might suggest a need to modify it. \n\n\tWe will post all comments we receive, without change, to http://dms.dot.gov , including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this AD. Using the search function of that Web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov. \n\nExamining the Docket \n\n\tYou may examine the 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 DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them. \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\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 the regulation: \n\n\t1. Is not a "significant regulatory action'' under Executive Order 12866; \n\n\t2. Is not a "significant rule'' under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\n\t3. 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):