A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain McDonnell Douglas Model DC-10-10, -15, -30, and -40 series airplanes, and Model KC- 10A (military) airplanes, was published in the Federal Register on August 30, 1995 (60 FR 45108). That action proposed to require inspection(s) to detect cracks of the attach bolts of the front spar support fitting of each wing, and replacement of attach bolts with ones that are corrosion-resistant. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\n\tOne commenter supports the proposal. \n\n\tAnother commenter requests that the proposal be revised to give operators "credit" for having accomplished the initial required ultrasonic inspection prior to the effective date of the final rule. This commenter is concerned that, if such credit is not specified in the AD, operators may be required to perform duplicate inspections needlessly. \n\n\tThe FAA acknowledges this commenter's concerns, and finds that some clarification is necessary. Operators are always given credit for work accomplished prior to the effective date of an AD by means of the phrase in the compliance section of the rule that states, "Required as indicated, unless accomplished previously." Since the ultrasonic inspection required by paragraph (a) of this AD is to be accomplished specifically in accordance with McDonnell Douglas DC-10 Service Bulletin 57-126, which was released on October 30, 1992, the possibility exists that some operators may have accomplished the initial ultrasonic inspection some years ago when the service bulletin was originally issued. For those operators, the "unless accomplished previously" phrase is intended to ensure that they not conduct a duplicate initial inspection. \n\n\tHowever, in light of this commenter's concerns, the FAA finds that the compliance time for repetitive inspections must be clarified. The intent of this AD is to establish a schedule of inspections that are to be conducted at 18-month intervals. Regardless of when the initial inspection was conducted, that inspection must be repeated within 18 months afterwards. Accordingly, paragraph (a) of the final rule has been revised to clarify that the initial inspection is required within 18 months after the effective date of the AD, unless it was accomplished previously within 18 months prior to the effective date. Paragraph (b) of the final rule has been clarified to specify that the inspection must then be repeated at an interval not to exceed 18 months after that initial inspection, and must be repeated again every 18 months after that. \n\n\tOne commenter states that the manufacturer has advised that it is developing revised procedures for accomplishment of the bolt replacement (which may include only partial replacement under certain conditions). The commenter requests that the FAA revise the proposed rule to make these new procedures available to affected operators. \n\n\tThe FAA concurs with the commenter's request. Since issuance of the proposal, the FAA has reviewed and approved McDonnell Douglas Service Bulletin DC1057-126, Revision 1, dated March 1, 1996. This revised service bulletin is essentially identical to the McDonnell Douglas DC-10 Service Bulletin 57-126, dated October 30, 1992, but provides procedures for replacing a minimum of 5 of the attach bolts of the front spar support fitting on each wing with corrosion- resistant attach bolts; and, at the next pylon removal after that replacement, replacing the remaining 1 attach bolt of the front spar support fitting on each wing. Accomplishment of the replacement of these six attach bolts eliminates the need for the repetitive inspections of them. These replacement procedures are identical to the procedures proposed in paragraph(b)(2) of the proposed rule. The FAA has revised the final rule to include the newly released (revised) service bulletin as an additional source of service information. \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 420 Model DC-10-10, -15, -30, and -40 series airplanes, and Model KC-10A (military) airplanes of the affected design in the worldwide fleet. The FAA estimates that 237 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 6 work hours per airplane to accomplish the required inspections, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the inspection requirements of this AD on U.S. operators is estimated to be $85,230, or $360 per airplane, per inspection cycle. \n\n\tIt will take approximately 6 work hours per airplane to accomplish the required bolt replacement, at an average labor rate of $60 per work hour. Required parts will cost approximately $43,000 per airplane. Based on these figures, the cost impact of the replacement requirements of this AD on U.S. operators is estimated to be $10,276,320, or $43,360 per airplane. \n\n\tThe number of work hours indicated above does not include time for gaining access, removing and reinstalling engines, removing and reinstalling pylons, closing up, or performing functional checks. Additionally, it does not include time for preparation for the replacement, administrative functions, or nonproductive elapsed time. \n\n\tThe cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\n\tThe regulations adopted herein will not have substantial direct effects 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. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \n\n\tFor the reasons discussed above, I certify that this action (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 (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. A final evaluation has been prepared for this action and it is contained in theRules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \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\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: \n\nAuthority: 49 USC 106(g), 40113, 44701. \n\n§ 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: