Discussion \n\n\tWe have received reports of loose, cracked, or missing fasteners in the aft mount support fitting of the left and right engines on several McDonnell Douglas Model MD-90-30 airplanes. The airplanes had accumulated between 18,767 and 25,400 total flight hours and between 15,841 and 27,000 total flight cycles. A safety assessment of the missing fasteners has concluded that loose or discrepant fasteners in the top horizontal row, common with the pylon skin, significantly decrease the margin of safety of the aft mount support installation at the design limit load. Loose, cracked, or missing fasteners in the engine aft mount support fitting could lead to separation of the support fitting from the pylon. This condition, if not corrected, could result in separation of the engine from the airplane. \n\nRelevant Service Information \n\n\tWe reviewed Boeing Alert Service Bulletin MD90-54A002, dated August 1, 2008. The service bulletin describes procedures for doing a detailed inspection for certain defects of the upper fasteners of the aft mount support fitting of the left and right engines, and corrective action as applicable. The detailed inspection consists of the following actions: (1) A general visual inspection of the upper fasteners for any missing, loose, or damaged fasteners, (2) a gap check between the washers and structure or between the fastener heads and structure, if applicable, and (3) a torque check of the fastener nuts, if applicable. The corrective action includes replacing all fasteners if any defect is found. \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. \n\nInterim Action \n\n\tThis is considered to be interim action until final action is identified, at which time we might consider further rulemaking. \n\nFAA's Justification and Determination of the Effective Date \n\n\tLoose, cracked, or missing fasteners in the engine aft mount support fitting could lead to separation of the support fitting from the pylon, possibly resulting in separation of the engine from the airplane. Because of our requirement to promote safe flight of civil aircraft and thus, the critical need to assure structural integrity of the engine aft mount support fitting 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 notice and 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-2008-0946; Directorate Identifier 2008-NM-147-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 amongthe various levels of government. \n\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a "significant regulatory action'' under Executive Order 12866, (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 amends Sec. 39.13 by adding the following new AD: