Boeing advises that, since 1993, it has received 17 reports of cracks, loose and broken bolts, and shim migration in the joint between the aft torque bulkhead and the strut- to-diagonal brace fitting on Boeing Model 757-200 series airplanes. Those conditions, if not corrected, could result in damage and consequent loss of the strut and engine from the airplane. \n\nOther Relevant Rulemaking \n\n\tOn May 25, 2004, we issued AD 2004-12-07, amendment 13666 (69 FR 33561, June 16, 2004). That AD applies to Boeing Model 757 series airplanes, line numbers 1 through 735 inclusive, equipped with Rolls Royce RB211 engines. \n\n\tThat AD requires modification of the nacelle strut and wing structure; and inspections for loose/missing fasteners of certain aft bulkhead fasteners, proper alignment of the middle gusset of the inboard side load fitting, cracking of certain fastener holes; and corrective action if necessary. That AD cites various revision levels of Boeing Service Bulletin 757-54-0035 as the appropriate source of service information for the required actions. \n\n\tThat AD also mandated inspections of the 20 fasteners that are subject to this new AD. The threshold for those initial inspections is 15,000 total flight cycles. We have received reports of missing or loose fasteners in the affected joint as low as approximately 7,500 total flight cycles. In addition, that AD mandated inspections of the 20 fasteners of airplanes modified in accordance with Boeing Service Bulletin 757-54-0035 (original), but did not mandate inspections for airplanes modified in accordance with Revisions 1 or 2 of that service bulletin or airplanes that had been modified in production. Loose or missing fasteners have been found on airplanes with all versions of the modification. \n\n\tThe actions required by that AD were intended to prevent fatigue cracking in primary strut structure and consequent reduced structural integrity of the strut, but based on this service experience, we have concluded that the inspection requirements of that AD are not adequate. \n\nRelevant Service Information \n\n\tWe have reviewed Boeing Service Bulletin 757-54A0047, Revision 1, dated March 24, 2005. The service bulletin describes procedures for repetitive detailed inspections of the shim installation between the vertical flange and bulkhead. Specifically, the service bulletin provides procedures to: \n\n\tInspect for damaged sealant around the shim; \n\n\tInspect for signs of shim movement; \n\n\tMeasure the horizontal and vertical movement of the shim from the installed position to determine the total cumulative movement of the shims; \n\n\tInspect for signs of movement of the four fasteners in the vertical flange; and \n\n\tDetect signs of damaged paint and/or sealant or signs of movement of the 16 fasteners that hold the bulkhead assembly to the horizontal flange of the strut-to-diagonal brace fitting. \n\n\tThe service bulletin also describes four different interim repairs, depending on the amount of shim movement revealed during the inspections. The various interim repair actions include doing an eddy current inspection of the fastener holes for cracks, for which the service bulletin recommends contacting the manufacturer for repair instructions; replacing the shims with new shims; oversizing the holes and replacing discrepant fasteners with oversize fasteners; and applying sealant/primer on the shim of the vertical flange. \n\n\tFor airplanes modified in accordance with Service Bulletin 757-54- 0035, the compliance time for the initial inspection is 6,000 flight cycles/36 months after the modification, with a grace period of 3,000 flight cycles/18 months. For unmodified airplanes, the compliance time is 90 days. The repetitive intervals range from 6,000 to 9,000 flight cycles/36 to 54 months. Interim repairs are due before further flight after a positive finding. \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. Therefore, we are issuing this AD to detect and correct cracks, loose and broken bolts, and shim migration in the joint between the aft torque bulkhead and the strut-to-diagonal brace fitting. These conditions could result in damage to the strut and consequent separation of the strut and engine from the airplane. This AD requires accomplishing the actions specified in the service information described previously, except as discussed below. \n\nDifferences Between the AD and the Service Bulletin \n\n\tThe service bulletin specifies compliance times relative to the issue date of the service bulletin; this AD requires corresponding compliance times relative to the effective date of the AD. \n\n\tThe service bulletin specifies that you may contact the manufacturer for instructions on howto repair certain conditions, but this proposed AD would require you to repair those conditions using either a method that we approve, or data that meet the certification basis of the airplane and have been approved by an Authorized Representative for the Boeing Delegation Option Authorization Organization whom we have authorized to make those findings. \n\nClarification of Certain Compliance Times \n\n\tFor Group 2 airplanes, the service bulletin specifies an inspection threshold relative to the date of issuance of the "original Airworthiness Certificate * * *" For these same airplanes, however, this AD requires an inspection threshold relative to the date of issuance of the "original standard airworthiness certificate * * *" We find that the addition of the term "standard" will establish this date with certainty. \n\nFAA's Determination of the Effective Date \n\n\tAn unsafe condition exists that requires the immediate adoption of this AD; therefore, providing notice and opportunity forpublic comment before the AD is issued is impracticable, and 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 under ADDRESSES. Include "Docket No. FAA-2005-21358; Directorate Identifier 2005-NM-088-AD" at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD. We will consider all comments received by the closing date and may amend the AD in light of those comments. \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 FAApersonnel concerning this AD. Using the search function of our docket 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 can review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you can visit http://dms.dot.gov. \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. 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\nPART 39--AIRWORTHINESS DIRECTIVES \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: 0 1. 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 airworthiness directive (AD):