Examining the Docket \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 certain Boeing Model 757 series airplanes. That NPRM was published in the Federal Register on September 21, 2004 (69 FR 56375). That NPRM proposed to require repetitive inspections for corrosion and cracking of the midspar fittings in the nacelle struts, and corrective actions if necessary. That NPRM also proposed to provide an optional terminating action for the repetitive inspections. \n\nExplanation of Revised Service Information \n\n\tSince we issued the NPRM, Boeing revised Special Attention Service Bulletin 757-54-0042, dated May 13, 1999, which was specified in the NPRM as the appropriate source of service information for accomplishing the proposed requirements of this AD. We have reviewed Boeing Service Bulletin 757-54-0042, Revision 1, dated July 7, 2005, which, among other changes, incorporates the information specified in Boeing Information Notices 757-54-0042 IN 01, dated July 22, 1999; 757-54-0042 IN 02, dated January 6, 2000; and 757-54-0042 IN 03, dated November 21, 2000; revises incorrect part number references; and contains a revised Figure 6. \n\n\tFigure 6 of Service Bulletin 757-54-0042, Revision 1, specifies an optional action to replacing any cracked or corroded midspar fitting. That option involves one-time high-frequency eddy current (HFEC) and borescope inspections to detect corrosion or cracking within the fitting bolt holes. Revision 1 also describes the related repair of any cracked or corroded bolt hole; and repetitive detailed inspections and general visual inspections for recurrent corrosion or cracking of the repaired fitting until the fitting is replaced. We have determined that these new inspections and corrective actions are adequate to maintain airplane operational safety, and we have revised the AD to refer to Service Bulletin 757-54-0042, Revision 1, as the appropriate source of service information for accomplishing the requirements of the AD, except as discussed under "Difference Between Service Information and This AD.'' \n\nDifference Between Service Information and This AD \n\n\tService Bulletin 757-54-0042, Revision 1, specifies to contact the manufacturer for instructions on how to repair certain conditions, but this AD requires repairing those conditions in one of the following ways: \n\n\tUsing a method that we approve; or \n\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\nComments \n\n\tWe provided the public the opportunity to participate in the development of this AD. We have considered the comments received. \n\nAD Not Applicable \n\n\tOne commenter, American Airlines, states that none of its airplanes are affected by this AD. \n\nRequest To Correct Errors in Service Information \n\n\tTwo commenters, ATA and UPS, request that we revise the service information. The commenters state that Boeing has released 3 INs that correct errors in the service bulletins, but that the INs are not FAA- approved. Therefore, the commenters assert that the INs should be incorporated in the service bulletin before the AD is released. \n\n\tWe agree with this request, as Boeing has revised the service bulletin to incorporate the INs as previously discussed. The AD has been changed to specify the revised service bulletin as the appropriate source of service information. \n\nRequest for Delayed Replacement of Fittings \n\n\tOne commenter, Boeing, requests that we allow up to 18 months to replace any midspar fitting following the detection of corrosion of that fitting. The commenter states that the additional inspections and actions specified in Service Bulletin 757-54-0042, Revision 1, will allow the airplane to operate safely for up to 18 months without replacing the corroded midspar fitting. \n\n\tWe agree with this request, as we have agreed to update the service information reference as previously discussed. We have revised paragraphs (h) and (i) of the NPRM and added new paragraph (j) to describe the corrective actions. We have added new paragraph (k) to describe optional investigative actions which would allow up to 18 months to replace any midspar fitting discovered with signs of corrosion or cracking; and to clarify the fitting repair, repetitive inspection, and replacement instructions of Service Bulletin 757-54- 0042, Revision 1. We added new paragraph (m) to give credit for actions accomplished prior to the effective date of this AD in accordance with Boeing Special Attention Service Bulletin 757-54-0042, dated May 13, 1999. Consequently, we have re-identified existing paragraphs (j), (k), and (l) of the NPRM as paragraphs (l), (n), and (o) in this AD. \n\nRequest To Develop Non-Destructive Test for Cracking \n\n\tOne commenter, ATA, requests that a non-destructive testing (NDT) procedure for cracking be developed prior to the release of the final rule. This NDT procedure would apply to holes that display evidence of corrosion. The commenter states that, though such a procedure does not exist for Model 757 airplanes, such procedures do exist and are required for Model 767 airplanes. \n\n\tWe agree with this request. As discussed previously, Service Bulletin 757-54-0042, Revision 1, specifies new NDT procedures for HFEC and borescope inspections of the midspar fitting bolt holes, and we have revised the AD to require these inspections, if corrosion or cracking is found and the fitting is not immediately replaced with a new, improved fitting. \n\nRequest To Permit Continued Operation After Staining Discovered \n\n\tOne commenter, UPS, requests that continued operation be permitted after the discovery of staining on the fittings. The commenter states that fittings discovered to have corrosion stains after multiple repetitions of the 300-flight-cycle inspection should be inspected in greater detail to determine the extent of the corrosion. The commenter gives no technical justification for this request. \n\n\tWe do not agree with this request. The commenter asserts the service bulletin states that, after the discovery of staining, no corrective actions need be taken until several repetitions of the 300 flight cycle inspection have been accomplished, at which time further investigative actions would be appropriate. However, staining is evidence of active corrosion andstress corrosion cracking (SCC) is time dependent; the longer a corroded fitting remains in service with no corrective action, the more likely it becomes that a crack will start and propagate, with possible consequent failure of the fitting. We have not changed this AD in this regard. \n\nRequest To Reinstate 300-Flight-Cycle Inspection and Lubrication Interval \n\n\tTwo commenters, ATA and United Airlines, request that the 300- flight-cycle interval for inspection and lubrication originally specified by Special Attention Service Bulletin 757-54-0042 be reinstated. One commenter states that a general visual inspection of the midspar fittings revealed no corrosion or cracking. The commenters feel that inspection and lubrication performed every 300 flight cycles should permit airplane operation with adequate safety. \n\n\tWe do not agree with this request. We examined a midspar fitting, which showed major corrosion at the faying surface around one bolt hole with a crack emanating from thatbolt hole. Further, another crack emanated from a second bolt hole. Therefore, we do not agree that inspection and lubrication as suggested by the commenters would provide adequate airplane safety. However, as previously discussed, Service Bulletin 757-54-0042, Revision 1, specifies HFEC and borescope inspections of the bolt holes of any cracked or corroded midspar fitting and, provided necessary corrective action is taken after those inspections, permits continued operation of the airplane as long as repetitive detailed inspections of any repaired fitting are performed until the fitting is replaced, and we have revised the AD to reflect this. \n\nRequest To Withdraw Proposed AD \n\n\tOne commenter, ATA, requests that we withdraw the proposed AD. The commenter states that the AD is not necessary, since only one midspar fitting has been found with cracking, and asserts operators should be able to wait to inspect, repair, and replace any subject midspar fittings until the Model 757 StrutImprovement Program (SIP) can be accomplished. \n\n\tWe do not agree. While the threshold for the SIP program is at twenty years (240 months) or 37,500 flight cycles, whichever occurs first, the cracked midspar fitting was discovered on an airplane that was about 17 years old and had accumulated less than 30,000 total flight cycles. Further, the damaged fitting showed two cracks that had propagated from SCC, and, as the suspect fittings are made of heat- treated 4330M stock, all mounting holes of such fittings are susceptible to SCC. The actions specified in this AD are necessary to ensure adequate airplane safety prior to accomplishing the SIP; therefore, the AD will not be withdrawn. \n\nRequest To Correct Threshold Limits \n\n\tTwo commenters, United Airlines and UPS, state that the threshold limits specified in the "Other Related Rulemaking'' paragraph of the NPRM are incorrect. Though the commenters do not make a request or provide data to support this position, it appears the commenters wish us to revise those limits. \n\n\tWe do not agree. Although paragraph (d) of AD 2003-18-05, amendment 39-13296 (68 FR 53496, September 11, 2003), requires replacing the upper link of the strut in accordance with Boeing Service Bulletin 757- 54-0036, dated May 14, 1998, prior to the accumulation of 27,000 total flight cycles for Model 757-200 airplanes or 29,000 total flight cycles for Model 757-200PF airplanes, the threshold for the entire SIP remains at 20 years or 37,000 flight cycles, whichever occurs first. Our intent was to give credit to operators who have already accomplished the SIP, but we acknowledge that discussing these threshold limits could have caused confusion. However, as the "Other Related Rulemaking'' paragraph of the NPRM is not repeated in the final rule, no change is needed to this AD in this regard. \n\nExplanation of Change to Applicability \n\n\tWe have revised the applicability of the existing AD to identify model designations as published in the mostrecent type certificate data sheet for the affected models. \n\nClarification of AMOC Paragraph \n\n\tWe have revised this action to clarify the appropriate procedure for notifying the principal inspector before using any approved AMOC on any airplane to which the AMOC applies. \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 with the changes described previously, as well as certain minor editorial changes. We have determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCosts of Compliance \n\n\tThis AD will affect about 410 airplanes worldwide. 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.-\nregisterred airplanes \nFleet cost \n\n\n\n\n\n\n\n\n\n\n\n\n\n\nInspection, per inspection cycle \n3 \n$65 \nNone \n$195, per inspection \ncycle \n338 \n$65,910, per \ninspection \ncycle \n\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 inthis 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):