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 Boeing Model 747 series airplanes was published in the Federal Register on February 7, 1995 (60 FR 7140). That action proposed to require modification of the nacelle strut and wing structure, inspections and checks to detect discrepancies in the adjacent structure, and correction of discrepancies. \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\tTwo commenters support the proposed rule.\n\n Revision of Descriptive Language \n\n\tOne commenter notes that the description of the unsafe condition that appeared in the Discussion section of the preamble to the notice refers to "the structural fail-safe capability of the strut-to-wing attachment." The commenter states that this description is inaccurate, since it implies that the strut-to-wing attachment is inadequate. The commenter suggests that a more accurate description would be "damage tolerance capability of the strut-to-wing attachment." The FAA acknowledges that the commenter's wording is more accurate. The pertinent wording in the preamble to the final rule has been revised to reflect this change. Furthermore, the FAA considers the new structure of the strut as meeting the damage tolerance requirements of amendment 45 of section 25.571, "Damage--tolerance and fatigue evaluation of structure" of the Federal Aviation Regulations (14 CFR 25.571, amendment 45), which provides an even higher level of safety than simply fail-safe requirements. \n\n\tThis same commenter provides additional information to describe the purpose of the proposed modification of the nacelle strut and wing structure. This commenter suggests that the rule should specify that the modification not only significantly improves the load-carryingand durability of the strut-to-wing attachments, but "reduces the reliance on non-routine inspections," as well. The FAA concurs with this suggestion and has revised the Summary section of the preamble to this final rule to include wording relevant to this aspect. \n\n\tThis commenter also provides further clarification of the description of the requirements of the existing AD's that address unsafe conditions associated with the strut attachment assemblies on Model 747 series airplanes equipped with Rolls Royce Model RB211 series engines. The description in the Discussion section of the preamble to the proposal states that the existing AD's require "inspections of the strut, and strut-to-wing attachment structure." The commenter states that a more complete description of the existing AD's would be "inspections of the strut fuse pins, and strut-to-wing attachment structure." The FAA concurs that the commenter's wording is clearer. However, the following provides a more complete description: The existing AD's require "inspections of the diagonal brace and midspar fuse pins, and strut-to-wing attachment structure." Since the Discussion section is not restated in this final rule, no change to the final rule is necessary. \n\nAD's Terminated by this Final Rule \n\n\tAdditionally, this commenter requests a revision of proposed paragraph (c), which lists the AD's that will be terminated upon accomplishment of the proposed modification of the nacelle strut and wing structure. The commenter states that since AD 79-17-07, amendment 39-3533, is not applicable to Model 747 series airplanes equipped with Rolls Royce Model RB211 series engines, that AD should be removed from the list. The FAA concurs; paragraph (c) of the final rule has been revised accordingly.\n\n Conclusion \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\nCost Estimate \n\n\tCurrently, there are no Model 747 series airplanes of the affected design, equipped with Rolls Royce Model RB211 series engines, on the U.S. Register. However, should an affected airplane be imported and placed on the U.S. Register in the future, it will require approximately 6,545 work hours to accomplish the required actions, at an average labor charge of $60 per work hour. The manufacturer will incur the cost of labor, on a pro-rated basis, with 20 years being the expected life of these airplanes. The median age for the fleet of Model 747 series airplanes equipped with Rolls Royce Model RB211 series engines is estimated to be 6 years. Required parts will be supplied by the manufacturer at no cost to operators. Based on these figures, the total cost impact of this AD will be $117,810 per airplane.This cost impact figure does not reflect the cost of the terminating actions described in the service bulletins listed in paragraph I.C., Table 2, "Prior or Concurrent Service Bulletins," on page 5 of Boeing Alert Service Bulletin 747-54A2157, dated January 12, 1995, that are required to be accomplished prior to, or concurrently with, the modification of the nacelle strut and wing structure. Since some operators may have accomplished certain modifications on some or all of the airplanes in its fleet, while other operators may not have accomplished any of the modifications on any of the airplanes in its fleet, the FAA is unable to provide a reasonable estimate of the cost of accomplishing the terminating actions described in the service bulletins listed in Table 2 of the Boeing alert service bulletin. \n\n\tThe cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplishthose actions in the future if this AD were not adopted. \n\n\tThe FAA recognizes that the obligation to maintain aircraft in an airworthy condition is vital, but sometimes expensive. Because AD's require specific actions to address specific unsafe conditions, they appear to impose costs that would not otherwise be borne by operators. However, because of the general obligation of operators to maintain aircraft in an airworthy condition, this appearance is deceptive. Attributing those costs solely to the issuance of this AD is unrealistic because, in the interest of maintaining safe aircraft, prudent operators would accomplish the required actions even if they were not required to do so by the AD. \n\n\tA full cost-benefit analysis has not been accomplished for this AD. As a matter of law, in order to be airworthy, an aircraft must conform to its type design and be in a condition for safe operation. The type design is approved only after the FAA makes a determination that it complieswith all applicable airworthiness requirements. In adopting and maintaining those requirements, the FAA has already made the determination that they establish a level of safety that is cost- beneficial. When the FAA, as in this AD action, makes a finding of an unsafe condition, this means that the original cost-beneficial level of safety is no longer being achieved and that the required actions are necessary to restore that level of safety. Because this level of safety has already been determined to be cost-beneficial, a full cost-benefit analysis for this AD would be redundant and unnecessary.\n\n Regulatory Impact \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 the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."\n\n List 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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive: