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 747-100, -200, and 747SP series airplanes was published in the Federal Register on August 31, 1999 (64 FR 47440). That action proposed to require repetitive detailed visual and ultrasonic inspections to detect missing, damaged, or broken taperlock bolts in the diagonal brace underwing fittings; and corrective actions, if necessary. That action also proposed to require eventual replacement of the aft 10 taperlock bolts with new bolts as terminating action for the repetitive inspections. \n\nComments \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\nSupport for the Proposal \n\n\tOne commenter supports the proposed rule. \n\nRequest to Reference Other Terminating ActionOne commenter requests that the FAA revise the notice of proposed rulemaking (NPRM) to reference accomplishment of Boeing Service Bulletin 747-57-2288 as terminating action for the repetitive inspection requirements proposed in the NPRM. The commenter states that accomplishment of the replacement of the diagonal brace underwing fitting in accordance with Figures 5 through 9 of that service bulletin, or the clearance adjustment in accordance with Figure 10 of that service bulletin, includes replacement of the same taperlock bolts with new bolts as described in the NPRM and in Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998 (which was referenced as the appropriate source of service information for the actions proposed in the NPRM). The commenter states that if the taperlocks that are the subject of this AD have already been replaced with the same new bolts that are specified in this AD, the operator should not be required to do the inspections proposed in the NPRM or apply for approval of an alternative method of compliance. The commenter states that if its request is granted and incorporated in the final rule, operators and the FAA will not have to process as many applications for alternative methods of compliance. \n\n\tThe FAA concurs with the commenter's request. The FAA finds that accomplishment of the replacement of the diagonal brace underwing fitting or the clearance adjustment described in Boeing Service Bulletin 747-57-2288, Revision 1, dated June 26, 1997, is acceptable for compliance with the requirements of paragraph (d) of this AD. Accordingly, a new NOTE 3 has been added to this final rule. However, the FAA finds that accomplishment of such replacement or clearance adjustment in accordance with the original issue of Boeing Service Bulletin 747-57-2288, dated September 15, 1994, is not acceptable for compliance with paragraph (d) of this AD, because that service bulletin does not specify to replace the taperlock bolts that are subjectto this AD.\n\nRequest to Clarify "Spares" Paragraph \n\n\tOne commenter requests that the FAA revise paragraph (e) of the NPRM to change the words "on any airplane" to "on any Boeing 747 airplane that is listed in the effectivity of (Boeing Service Bulletin) 747-57A2308." The commenter states that an operator was confused about the meaning of the paragraph as it is phrased in the NPRM. The FAA concurs with the intent of the commenter's request. The FAA acknowledges that the language used in the NPRM may confuse some operators. Therefore, paragraph (e) of this final rule has been revised to state that, "...no person shall install a bolt, part number BACB30PE( ) * ( ), or any other bolt made of 4340, 8740, or PH13-8 Mo steel, in the locations specified in this AD, on any airplane listed in the applicability of this AD." \n\nRequest to Revise Estimated Cost of Terminating Action \n\n\tOne commenter requests that the FAA revise the estimated cost of the terminating action, as quoted inthe proposed rule. The commenter points out that the number of work hours for accomplishment of the terminating action stated in the NPRM (i.e., 8 work hours) is inconsistent with the estimate in Boeing Alert Service Bulletin 747-57A2308. The commenter estimates that 248 to 306 work hours per airplane is necessary to accomplish the proposed replacement of taperlock bolts. \n\n\tThe FAA partially concurs with the commenter's request. The FAA does not concur with the commenter's estimate of 248 to 306 work hours, because that estimate includes time to gain access and close up. The cost analysis in AD rulemaking actions typically does not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. Because such incidental costs may vary significantly from operator to operator, they are almost impossible to calculate. However, the FAA finds that the number of work hours necessary for accomplishment of the terminating action is underestimated in the NPRM. The FAA estimates that the terminating action will take 68 work hours for airplanes in Groups 1, 2, and 5, and 125 work hours for airplanes in Groups 3 and 4. (These estimates coincide with Boeing's estimate for the number of work hours necessary to accomplish the terminating action if it is accomplished concurrently with other strut modifications.) The FAA has revised the cost impact information in this final rule accordingly. \n\nRequest to Delete Terminating Action Requirement \n\n\tOne commenter requests that the FAA revise the NPRM to delete the requirement to replace the subject taperlocks within 48 months after the effective date of this AD. The commenter states that the diagonal-brace-to-wing attachment can carry ultimate load with a certain number of failed taperlocks. The commenter asserts that the visual and ultrasonic inspections that are proposed in the NPRM will reliably detect bolt fractures before multiplefractures occur, and will ensure that the outboard engines and struts will not separate from the airplane. Furthermore, the commenter states that removing the subject taperlocks is a difficult and time-consuming procedure, necessitating costs and downtime not commensurate with the degree of enhanced flight safety. \n\n\tThe FAA does not concur with the commenter's request. As stated in the "Differences Between Proposed Rule and Service Bulletin" section of the NPRM, the FAA has determined that long-term inspections may not provide the degree of safety assurance necessary for the transport airplane fleet. The commenter supplied no data (such as the crack growth rate after inspection, to ensure that the inspection interval is adequate for timely detection of cracking) to support its statement that inspections will reliably detect bolt fractures before multiple fractures occur. The FAA finds that no change to the final rule is necessary in this regard. \n\nRequest to Allow Installationof Cadmium-Plated Taperlock Bolts \n\n\tOne commenter requests that the FAA revise paragraph (e) of the NPRM to state that taperlock bolts made of 4340, 8740, or PH13-8 Mo steel with no coating or with aluminum coating may be installed. (Paragraph (e) of the NPRM states that no bolt made of 4340, 8740, or PH13-8 Mo steel-regardless of the type of coating-may be installed.) The commenter states that it has had no service problems with cadmium-plated 4340, 8740, or PH13-8 Mo steel taperlock bolts, and further states that such cadmium-plated 4340 and 8740 steel taperlock bolts are approved for use in the Boeing 747 Structural Repair Manual, which is approved by the FAA. \n\n\tThe FAA does not concur with the commenter's request to allow use of cadmium-plated steel taperlock bolts. The terminating action required by this AD requires installation of BACB30NX*K* bolts. The material that these bolts are made of is less susceptible to stress corrosion cracking than the bolts with cadmium plating that the commenter specifies. In addition, the FAA has determined that BACB30NX*K* bolts are not listed in Boeing 747 Structural Repair Manual, Chapter 51-30-03, Figure 1, Sheet 37. Therefore, cadmium-plated 4340 and 8740 steel taperlock bolts are not approved for use in place of the BACB30NX*K* bolts required by this AD. No change to the final rule is necessary in this regard. \n\nConclusion \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 Impact \n\n\tThere are approximately 274 Model 747-100, -200, and 747SP series airplanes of the affected design in the worldwide fleet. The FAA estimates that 122 airplanes of U.S. registry will be affected by this AD. \n\n\tIt willtake approximately 1 work hour per airplane to accomplish the required inspection, at the average labor rate of $60 per work hour. Based on these figures, the cost impact of the required inspection on U.S. operators is estimated to be $7,320, or $60 per airplane, per inspection cycle. \n\n\tIt will take approximately 68 work hours per airplane to accomplish the required terminating action for airplanes included in Groups 1, 2, and 5, as specified in the service bulletin. It will take approximately 125 work hours to accomplish the required terminating action for airplanes included in Groups 3 and 4, as specified in the service bulletin. \n\n\tThe average labor rate is $60 per work hour. Required parts will cost approximately $8,008 per airplane. Based on these figures, the cost impact of the required terminating action on U.S. operators is estimated to be $12,088 per airplane, for airplanes in Groups 1, 2, and 5; and $15,508 per airplane, for airplanes in Groups 3 and 4. \n\n\tThe costimpact 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\n\tThe 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\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\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: Authority: 49 U.S.C. 106(g), 40113, 44701. \n§ 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: