The FAA has received reports indicating that fuel leakage of the wing center section has occurred on several Boeing Model 727 series airplanes due to cracking of the rear spar web of the wing center section. The cracking initiates on the forward side of the spar and propagates through the web at the upper machined land radius between Left Body Buttock Line (BBL) 40 and Right BBL 40. In two instances, cracking was reported on airplanes that had accumulated less than 25,000 total flight cycles. In another case, fuel leakage resulted in fuel odors being emitted into the cabin area. Investigation revealed that fuel was leaking into the airflow multiplier. Fuel leakage into the airflow multiplier due to cracking of the rear spar web of the wing center section, if not detected and corrected, could result in an electrical short that could cause a fire. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert ServiceBulletin 727-57A0182, dated September 18, 1997. This alert service bulletin describes procedures for removing the access panels of the wing center section to perform repetitive visual inspections using a borescope, or ultrasonic with high frequency eddy current inspections, to detect cracking of the rear spar web or fuel leakage of the wing center section, and repair, if necessary. \n\n\tIn addition, the alert service bulletin describes procedures for modification of the rear spar web of the wing center section to prevent cracking of the rear spar web, which eliminates the need for the repetitive inspections. The modification involves stop drilling any cracking, and repairing the rear spar web. \n\n\tThe alert service bulletin references Boeing Drawing 65C37620 as an additional source of service information for accomplishment of the repair and modification. \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 727 series airplanes of the same type design, this AD is being issued to detect and correct cracking of the rear spar web, which could permit fuel leakage into the airflow multiplier and resultant electrical shorting and fire. This AD requires repetitive inspections (either visual inspections using a borescope or a mirror, or ultrasonic and high frequency eddy current (HFEC) inspections) to detect cracking of the rear spar web or fuel leakage of the wing center section, and repair, if necessary. This AD also provides for an optional modification of the rear spar web of the wing center section, which constitutes terminating action for the repetitive inspection requirements of this AD. The inspections, certain repairs, and the modification are required to be accomplished in accordance with the alert service bulletin described previously. Certain repairs are required to be accomplished in accordance with a method approved by the FAA. \n\nDifferences Betweenthe AD and the Service Information \n\n\tOperators should note the following differences between this AD and the Boeing alert service bulletin: \n\n\t* Although the alert service bulletin recommends an initial inspection threshold of within 500 flight cycles for airplanes that have accumulated between 15,000 and 25,000 total flight cycles, and an initial inspection threshold of within 300 flight cycles for airplanes that have accumulated 25,000 or more total flight cycles, this AD specifies an initial compliance time of "prior to the accumulation of 15,000 total flight cycles, or within 300 flight cycles after the effective date of this AD, whichever occurs later." The FAA finds that, in view of the reports of cracking of the rear spar web on two airplanes that had accumulated less than 25,000 total flight cycles, the initial compliance time specified in this AD is appropriate. Further, the FAA finds that adequate justification for permitting an inspection threshold of 500 flight cycles for airplanes that have accumulated over 15,000 total flight cycles, but under 25,000 total flight cycles, has not been presented. Therefore, an initial inspection is required to be accomplished on all airplanes within 300 flight cycles after the effective date of this AD. \n\n\t* This AD requires that, for any cracking or fuel leakage detected that is outside the areas specified in the alert service bulletin, repair must be accomplished in accordance with a method approved by the FAA. \n\n\t* This AD requires that the access panel only be opened in order to perform the inspections, rather than removed, as described in the Boeing alert service bulletin. The manufacturer has advised the FAA that procedures to remove the access panels were inadvertently included in the alert service bulletin and will be removed at the next revision of the alert service bulletin. \n\n\t* Although the alert service bulletin describes procedures for performing the visual inspection using a borescope, the manufacturer has advised the FAA that the option of performing the visual inspection using a mirror was inadvertently omitted from the alert service bulletin. Moreover, Figure 1 of the Accomplishment Instructions of the alert service bulletin specifies that the subject area can be examined with a borescope or mirror. Therefore, the FAA has included the option of using a mirror as an acceptable method of compliance with the visual inspection requirements of this AD. \n\nInterim Action \n\n\tThis is considered to be interim action. The FAA is currently considering requiring the modification of the rear spar web of the wing center section, which will constitute terminating action for the repetitive inspections required by this AD. However, the planned compliance time for the installation of the modification is sufficiently long so that notice and opportunity for prior public comment will be practicable. \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-282-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 atthe 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\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: