A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 99-07-06, amendment 39-11091 (64 FR 14578, March 26, 1999), which is applicable to certain Boeing Model 767 series airplanes, was published in the Federal Register on June 23, 1999 (64 FR 33437). The action proposed to supersede AD 99-07-06 to continue to require repetitive inspections to detect cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, and follow-on actions, if necessary. That action also proposed to require accomplishment of the previously optional terminating action. \n\nComments \n\nInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\nSupport for the Proposal \n\nTwo commenters support the proposed rule. \n\nRequests to Revise Compliance Time \n\nOne commenter requests that the compliance time for the repetitive inspection intervals specified in paragraph (b)(1) of the proposed AD be extended. The commenter suggests that the inspection intervals should coincide with its current heavy maintenance program, which specifies that inspections be performed between 1,200 and 1,300 flight cycles. The commenter further states that to carry out the inspection at intervals not to exceed 1,000 flight cycles would be considered punitive action as it is prior to the normally scheduled maintenance. \n\nThe FAA does not concur with the commenter's request to extend the compliance time for accomplishment of the repetitive inspection intervals to between 1,200 and 1,300 flight cycles after the initial inspection. In developing an appropriate compliance time for the repetitive inspections, the FAA considered not only the degree of urgency associated with addressing cracking or damage of the forward and aft lugs of the diagonal brace of the nacelle strut, but other factors as well. Those factors include the recommendations of the manufacturer, and the practical aspect of accomplishing the repetitive inspections within an interval of time coinciding with normally scheduled maintenance for the majority of affected operators. Considering those factors, the FAA has determined that the compliance time of 1,000 flight cycles after the accomplishment of the initial inspection represents the maximum interval in which the affected airlines can continue to operate without compromising safety. In view of those factors, and the amount of time that has already elapsed since issuance of the notice of proposed rulemaking, the FAA has determined that further delay of these inspections is, in general, not appropriate. The FAA may, however, approve a request for an adjustment of the compliance time under the provisions of paragraph (f) of this final rule if data are submitted to substantiate that such an adjustment would provide an equivalent level of safety. No change to the final ruleis necessary in this regard. \n\nAnother commenter requests that the compliance times for the replacement of the diagonal brace specified in paragraphs (d) and (e) of the proposed rule be changed to reflect the flight cycle threshold formula specified in the structural inspection program service bulletin, 767-54-0081, Figure 1, which is to be released soon. The commenter also notes that the threshold formula could be placed in an appendix to the proposal. \n\nThe FAA does not concur with the commenter's request. Boeing Service Bulletin 767-54-0081 states that the threshold formula may be used in lieu of the calendar threshold specified in the identified service bulletins. The formula in service bulletin 767-54-0081 was FAA-approved based on the fact that certain airplanes (e.g., those that have extended flights) would reach the 20-year calendar threshold long before they accumulated the flight cycle threshold of 37,500 total flight cycles specified in that service bulletin. The FAA notes that there is no comparable threshold in calendar time contained in this final rule for which the proposed threshold formula can be used as a substitute. The FAA considered many factors (as stated previously) before developing an appropriate compliance time for this AD, and the FAA has determined that the compliance time for the replacement required by paragraphs (d) and (e) of the final rule represents the maximum interval in which the affected airlines can continue to operate without compromising safety. Therefore, no change to the final rule is necessary. \n\nAnother commenter requests the compliance time in paragraph (b)(2) of the proposal be revised to read, "...diagonal brace has accumulated 24,000 flight cycles..." to agree with the alert service bulletin. The FAA does not concur. The alert service bulletin specifies that the initial inspection for Group 2 airplanes be performed prior to the accumulation of 24,000 flight cycles, or within 90 days after receipt of theservice bulletin; and the repetitive inspections be performed at intervals not to exceed 3,000 flight cycles until the diagonal brace has accumulated 32,000 flight cycles. Therefore, the final rule agrees with the alert service bulletin and no change is necessary in this regard. \n\nRequest to Revise Paragraphs (a), (b), and (c) of the Proposed Rule \n\nThree commenters request that the word "damage" be deleted from or clarified in paragraphs (a), (b), and (c) of the proposal. \n\nThe first commenter states that, if any damage is detected, even if it is minor and repairable, replacement of the diagonal brace is required, as specified in paragraph (c) of the proposal. The commenter further states that the alert service bulletin referenced in the proposal specifies an inspection to detect cracking of the diagonal brace lugs only, and does not specify inspecting for damage; therefore, the word "damage" should be deleted. \n\nThe second commenter states that if the words "or damage" arenot removed, paragraphs (a), (b), and (c) of the proposal should specifically clarify what should be searched for (cracks, fracture) during the inspection. The same commenter requests the addition of a requirement in paragraph (c) of the proposal to specify that damage to the lug bores (including wear, cracks, or surface corrosion) be repaired in accordance with Part 2 of the Accomplishment Instructions of the alert service bulletin. \n\nThe third commenter states that the word "damage" is undefined in the proposed rule, and notes that the alert service bulletin specifies that cracks originated in the lug bore of the diagonal brace caused by bushing motion and subsequent fretting of the lug bore, indicating that the damage that caused the cracks was fretting of the lug bore. The commenter also notes that the detailed visual inspection required by paragraph (a) of the proposal does not inspect the lug bore; therefore, the fretting or "damage" will not be found. The commenter indicates that, without any damage limit guidelines, even very minor damage (tool marks, scratched paint) will make it necessary for operators to perform costly additional inspections. The commenter notes that the inspection should be limited to the unsafe condition that is caused by fretting of the lug bore, which can be found by crack indications. \n\nThe FAA does not concur with the commenters' requests concerning removal of the word "damage" as referenced in paragraphs (a), (b), and (c) of the final rule. The FAA has reviewed this issue and has determined that the inspection to detect cracks or damage as required by paragraphs (a) and (b) of the final rule, is necessary. Certain types of damage, if detected, specifically fretting and bushing motion, must be corrected in accordance with the Manager, Seattle Aircraft Certification Office. These types of damage are two links in a sequential chain of events that can ultimately result in a fractured lug, or other possible failure modes. Other types of damage (tool marks, scratched paint) are not related to the unsafe condition specified in this AD, and would be defined as superficial. The FAA has, however, added a "NOTE 2" to the final rule to define the word "damage." \n\nThe FAA concurs with the second commenter's request to add another requirement to paragraph (c) of the final rule, which states that damage can be repaired in accordance with the applicable service bulletin. Paragraph (c) of the final rule has been revised to give the operator the option of either repair or replacement of the diagonal brace if any cracking or damage is detected, following accomplishment of any inspection required by paragraph (a) or (b) of the AD. \n\nRequest for Clarification of Paragraph (c) of the Proposed Rule \n\nOne commenter requests that the wording in paragraph (c) of the proposal be revised to read, "...and if one or more ligaments of the lugs are fractured perform additional inspections to detect damage of the strut secondary load paths..." The commenter notes that cracking, rather than fractures, will not increase the load in the secondary load path. \n\nAnother commenter requests clarification of the requirements in paragraph (c) of the proposal. The commenter questions which two lugs out of the four lugs (two lugs on the forward end and two lugs on the aft end) of the diagonal brace must be fractured before the extensive follow-on inspections of the secondary load path structure (Figure 8 of the service bulletin) are necessary. The commenter's interpretation is that the inspections specified in Figure 8 of the service bulletin are necessary only if both lugs on one of the ends of the diagonal brace are fractured, and if only one lug on each end of the diagonal brace is fractured, the inspections specified in Figure 7 of the service bulletin would be necessary. \n\nThe FAA agrees that clarification is necessary in order to better define the requirements in paragraph (c) of the AD. Paragraph (c) ofthe final rule has been revised to provide a detailed explanation of the inspection area and procedures. \n\nConclusion \n\nAfter 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. Cost Impact \n\nThere are approximately 208 airplanes of the affected design in the worldwide fleet. The FAA estimates that 105 airplanes of U.S. registry will be affected by this AD. \n\nThe inspections that are currently required by AD 99-07-06, and retained in this AD, take approximately 1 work hour per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required inspections on U.S. operators is estimated to be $6,300, or $60 per airplane,per inspection cycle. \n\nThe replacement that is required in this AD action takes approximately 8 work hours (4 work hours for each strut) per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $50,000 per airplane. Based on these figures, the cost impact of the required replacement required by this AD on U.S. operators is estimated to be $5,300,400, or $50,480 per airplane. \n\nThe 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\nRegulatory Impact \n\nThe regulations adopted herein 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. \n\nFor 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\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: \nAuthority: 49 U.S.C. 106(g), 40113, 44701. \n§ 39.13 (Amended) \n\t2. Section 39.13 is amended by removing amendment 39-11091 (64 FR 14578, March 26, 1999), and by adding a new airworthiness directive (AD), amendment 39-11659, to read as follows: