A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes was published in the Federal Register on December 17, 1993 (58 FR 65943). That action proposed to require repetitive high frequency eddy current (HFEC) inspections to detect cracking in certain fuselage skin lap joints, and repair, if necessary. \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 proposed rule. \n\n\tOne commenter requests that Revision 1 of Boeing Service Bulletin 747-53-2367, dated January 27, 1994, be included as an additional source of service information. The FAA concurs. Since the issuance of the proposal, the FAA has reviewed and approved Revision 1 of Boeing Service Bulletin 747-53-2367, dated January 27, 1994, which clarifies the procedures for accomplishment of the inspections described in the Initial Release of the service bulletin, dated December 18, 1991 (which was referenced in the proposal as the sole source of appropriate service information). Therefore, paragraphs (a) and (c) of the final rule have been revised to reference Revision 1 of the service bulletin as an additional source of service information. \n\n\tThis same commenter requests that the proposed rule be revised to include a reporting requirement to keep Boeing and the FAA advised of findings of cracks. The FAA does not concur. The FAA has determined that the unsafe condition addressed by this AD (which is to detect and repair fatigue cracking in certain lap joints) will be adequately addressed by paragraph (a) of the final rule, which requires the inspection of certain lap joints, and paragraph (c) of the final rule, which requires the repair of all cracks found during the inspection. Therefore, since the final rule requires repetitive inspections to detect cracks and repair of all findings of cracks, the FAA finds that a reporting requirement would unduly burden operators. \n\n\tThis commenter further requests that the proposed rule be revised to compensate for operators that fly with cabin pressure differentials of 2.0 psi or less when calculating the number of flight cycles to determine the compliance time. The FAA does not concur. The FAA finds that operating at cabin pressure differentials of 2.0 psi or less is applicable to only one operator. Since there are numerous factors that affect the calculation of flight cycles, such as total number of low pressure cycles, amount of thrust, number of gross weight flight cycles, etc., the FAA has determined that these mitigating factors could be best evaluated through requests for alternative methods of compliance, as provided for in paragraph (d) of the final rule. \n\n\tOne commenter requests that the proposed compliance time of 22,000 flight cycles be extended to 25,000 flight cycles to inspect the lap joints in areas outside of Stringer 14 since data indicate that cracking in these areas did not occur until after 25,000 flight cycles. The FAA does not concur. In developing an appropriate compliance time for this AD, the FAA not only evaluated the fatigue test data that was provided by the manufacturer, but took into consideration the size of the test sample: the test results were based upon just one airplane that had no loads and was not pressurized. Based on this data, the FAA determined that 22,000 flight cycles represented a conservative threshold for initiating inspections so as to ensure that any cracking initiation would be found in a timely manner. \n\n\tAnother commenter requests that the proposed compliance time of 3,000 flight cycles to perform the repetitive inspections be extended to 4,300 flight cycles to coincide with operators' regularly scheduled maintenance periods. The FAA does not concur. The FAA has determined that the compliance time, as proposed, represents the maximum interval of time allowable for the affected airplanes to continue to operate without compromising safety. In developing this inspection interval, the FAA evaluated the reliability of the inspection method and the results of fatigue test data. The FAA found that extending this interval by more than one-third would allow cracks to propagate undetected, which would adversely affect the structural integrity of the airplane.\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 change previously described. The FAA has determined that this change will neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 723 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 183 airplanes of U.S. registry will be affected by this AD, that it will take approximately 14 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $140,910, or $770 per airplane. \n\n\tThe total 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. \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.For 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\nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows: \nPART 39 - AIRWORTHINESS DIRECTIVES \n\n1.\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\n2.\tSection 39.13 is amended by adding the following new airworthiness directive: