The FAA has received three reports indicating that fatigue cracking was found on the longeron splice fittings at stringer 11 on Boeing Model 747SR and 747-200 series airplanes. The most recent cracking was detected on an airplane that had accumulated 62,783 total flight hours and 16,867 total flight cycles. Such fatigue cracking, if not detected and corrected in a timely manner, could result in reduced controllability of the horizontal stabilizer.\n \nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2410, Revision 2, dated October 30, 1997, including Addendum, which describes procedures for repetitive detailed inspections to detect cracking of the longeron splice fittings at stringer 11, on the left and right sides at body station 2598, and replacement of any cracked fitting with a new fitting. The alert service bulletin specifies various compliance times for groups of airplanes having different flight hour and flight cycle thresholds.\n \nExplanation of the Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 747-100, 747-200, 747-300, 747SR, and 747SP series airplanes of the same type design, this AD requires a one-time detailed inspection to detect cracking of the longeron splice fittings at stringer 11, on the left and right sides at body station 2598, and replacement of any cracked fitting with a new fitting. The actions are required to be accomplished in accordance with the alert service bulletin described previously. \n\nDifferences between the AD and the Alert Service Bulletin \n\n\tThe AD differs from the previously described alert service bulletin in that the AD requires a one-time inspection and shortened compliance time, rather than the repetitive inspections and multiple compliance times specified in the referenced alert service bulletin. The recent report of cracking detected on a Boeing Model 747-200 series airplane at a relatively low threshold has indicated the need for interim action requiring inspection at an early date, directed to those airplanes that have accumulated the highest number of flight hours or flight cycles (i.e., 78,000 total flight hours or 22,000 total flight cycles). \n\n\tIn addition, the AD differs from the alert service bulletin by providing a compliance period in terms of calendar time, rather than flight cycles/hours, for those airplanes that have exceeded the threshold. Due to the limited availability of replacement fittings, a 90-day compliance period is provided by this AD. This compliance period will allow the operators of affected airplanes an opportunity to schedule the inspection and have necessary replacement fittings available if cracks are found during the inspection. \n\nInterim Action \n\n\tThis AD is considered to be interim action. The FAA is considering separate rulemaking action that would propose similar inspections at repetitive intervals for all airplanes affected by the previously described alert service bulletin. \n\nDetermination of Rule's Effective Date \n\n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 97-NM-294-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory 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\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \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\n PART 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. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: