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 all Boeing Model 747 series airplanes was published in the Federal Register on February 21, 2001 (66 FR 10974). That action proposed to require repetitive high frequency eddy current inspections to find cracking of the bulkhead frame support at body station 2598 under the hinge support fittings of the horizontal stabilizer, and repair if cracking is found. \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\nRevised Service Information \n\n\tTwo commenters ask that the FAA approve Boeing Service Bulletin 747-53A2449, Revision 1, dated May 24, 2001, as another source of service information for doing the actions specified in the proposed rule. The proposed rule cited Boeing Alert Service Bulletin 747-53A2449, dated June 8, 2000, as the proper source of service information for doing the specified actions. \n\n\tOne commenter, the manufacturer, states that the revised service bulletin changes the airplane effectivity by limiting the affected airplanes to line numbers (L/N) 1 through 1307, inclusive. Airplanes delivered after L/N 1307 have been redesigned to reduce the possibility of early cracking of the bulkhead in the subject area. The revised bulletin also corrects the bolt torque values specified in the original issue of the service bulletin. The commenter adds that using the torque values in the original issue could lead to over-torque of the bolts during installation. \n\n\tAnother commenter suggests that, when a revised service bulletin is released, it should specify the correct torque values for the shear bolts, or reference the Structural Repair Manual, Chapter 51-30-04 or 51-40-04. The commenter adds that the manufacturer informed the commenter by telex that, if theshear bolts are torqued per the service bulletin specified in the proposed rule, they will be over-torqued. The commenter does not intend to do the inspections until a revised service bulletin is issued, in order to minimize the risk of over-torquing the shear bolts and to avoid the need to rework and replace the bolts.\n\n\tThe FAA concurs with the commenters and has reviewed and approved Boeing Service Bulletin 747-53A2449, Revision 1, dated May 24, 2001; which is referenced in the final rule as the proper source of service information for doing the actions specified. Accordingly, the applicability section has been changed to specify Model 747 series airplanes, as listed in Revision 1 of the service bulletin; the number of airplanes, as well as the number of work hours, which were increased in Revision 1 of the service bulletin, have been changed in the cost impact section; and a new Note 2 has been added to specify that actions done before the effective date of this AD, per the original issue of the service bulletin, are acceptable for compliance with paragraph (a) of the final rule. \n\n\tAlthough the torque values have been corrected in the revised service bulletin, operators who used the incorrect torque values during re-installation of the bolts can wait until the next repeat inspection to use the correct torque values. We have determined that over-torqued bolts will not compromise safety, as long as the bolts are properly torqued during the next repeat inspection. \n\nExtend Compliance Time \n\n\tOne commenter asks that the compliance time for the proposed rule be extended from before the accumulation of 10,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later; to before the accumulation of 10,000 total flight cycles, or within 1,200 flight cycles after the effective date of this AD, whichever occurs later. The commenter states that its recommendation will allow the accomplishment of the initial inspection during its regularly scheduled heavy maintenance checks, while still maintaining an equivalent level of safety. \n\n\tThe FAA does not concur with the commenter's request because the cracking of the bulkhead frame support is caused by fatigue, which is contingent on the number of accumulated flight cycles. In developing an appropriate compliance time for this action, we considered not only the degree of urgency associated with addressing the subject unsafe condition, but the manufacturer's recommendation as to an appropriate compliance time, and the practical aspect of accomplishing the required inspection within an interval of time that parallels normal scheduled maintenance for the majority of affected operators. We have determined that before the accumulation of 10,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later, represents an appropriate compliance time allowable for the initial inspection to be accomplished during scheduled maintenance intervals. However, under the provisions of paragraph (c) of the final rule, we may approve requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. \n\nTerminating Action \n\n\tOne commenter asks that a terminating action, such as oversizing the subject fastener holes, be provided by the manufacturer. The commenter states that this would alleviate potential structural damage caused by the repeated fastener and sealant removal, and installation at a critical joint. The FAA agrees with the intent of the comment, but until the manufacturer provides adequate service information giving procedures for a terminating action, such action cannot be added. If terminating action becomes available in the future, we may consider additional rulemaking. 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 1,147 airplanes of the affected design in the worldwide fleet. The FAA estimates that 261 airplanes of U.S. registry will be affected by this AD, that it will take approximately 18 work hours (9 work hours per side) per airplane to accomplish the required inspections, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $281,880, or $1,080 per airplane, per inspection cycle. \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 accomplish those actions in the future if this AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. \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 (44FR 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: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive