AD 2000-08-08

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-600, -700, and -800 series airplanes. This action requires a one-time inspection to detect cracking of the rear spar stiffeners in the wing center section; and modification of crack-free stiffeners, or repair of cracked stiffeners. This amendment is prompted by a report of severed rear spar stiffeners of the center wing, which resulted in cracking in the adjacent keel beam structure. The actions specified in this AD are intended to prevent failure of the keel beam structure.

Final rule; request for comments

2000-08-08 BOEING: Amendment 39-11694. Docket 2000-NM-88-AD. \n\n\tApplicability: Model 737-600, -700, and -800 series airplanes; certificated in any category; line numbers 1 through 321 inclusive. \n\n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (b) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent failure of the keel beam structure, accomplish the following: Inspection \n\n\t(a)\tPrior to the accumulation of the total number of flight cycles specified by Table 1, "Compliance Thresholds," as applicable, of Boeing Service Bulletin 737-57-1253, dated December 16, 1999; or within 60 days after the effective date of this AD, whichever occurs later: Perform a one-time high-frequency eddy current inspection to detect cracking of the rear spar stiffeners that are located at the left and right buttock lines 6.15 of the wing center section, in accordance with the service bulletin. \n\n\t\t(1)\tIf no cracking is detected in either stiffener: Prior to further flight, install the preventive modification on that stiffener, in accordance with the service bulletin. \n\n\t\t(2)\tIf any cracking is found in either stiffener, prior to further flight, repair that stiffener in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA,Transport Airplane Directorate; or in accordance with data meeting the type certification of the airplane approved by a Boeing Company Designated Engineering Representative (DER) who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically reference this AD. \n\nAlternative Methods of Compliance \n\t(b)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n\n\tNOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\nSpecial Flight Permits \n\t(c)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. \n\nIncorporation by Reference \n\t(d)\tExcept as required by paragraph (a)(2) of this AD, the actions shall be done in accordance with Boeing Service Bulletin 737-57-1253, dated December 16, 1999. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\n\t(e)\tThis amendment becomes effective on May 9, 2000.

The FAA has received a report of severed rear spar stiffeners of the center wing, which were found during fatigue testing of the Model 737-800 series airplane. The cracks were located in the stiffeners at the left and right buttock lines 6.15, and initiated at fastener holes below the lower chord of the rear spar. The broken stiffeners were caused by actual stresses being higher than those used for design of the structure. Failure of the stiffeners caused cracking in the adjacent keel beam structure. This condition, if not corrected, could result in failure of the keel beam structure. \n\n\tModel 737-600 and -700 series airplanes have a similar structural design and are therefore also subject to the identified unsafe condition. \n\nExplanation of Relevant Service Information \n\tThe FAA has reviewed and approved Boeing Service Bulletin 737-57-1253, dated December 16, 1999, which describes procedures for a one-time high-frequency eddy current inspection to detect cracking in the rear spar stiffeners at the fastener holes below the lower rear spar chord of the wing center section. For crack-free stiffeners, the service bulletin recommends a preventive modification, which involves installing nested angles at the stiffeners at the left and right buttock lines 6.15. For any cracked stiffener, the service bulletin recommends, among other things, replacement of that stiffener. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. \n\nExplanation of the Requirements of the Rule \n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent failure of the keel beam structure. This AD requires accomplishment of the actions specified in the service bulletin described previously, except as discussed below. \n\nDifferences Between the Rule and Relevant Service Information \n\tThe service bulletin recommends that cracked stiffeners be replaced and that further repair be accomplished in accordance with instructions from Boeing. However, this AD requires that repair of any cracked stiffener be accomplished in accordance with a method approved by the FAA. \n\nDetermination of Rule's Effective Date \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\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 RulesDocket 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 submittedin response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2000-NM-88-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \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\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, February26, 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." \n\nList of Subjects in 14 CFR Part 39 \n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \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: \nPART 39 - AIRWORTHINESS DIRECTIVES \n\t1. The authority citation for part 39 continues to read as follows: \nAuthority: 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: