AD 2000-04-08

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-200C series airplanes. This action requires repetitive inspections to detect cracking in the lower skin at the stringer 4R lap joint, and certain fuselage frames; and corrective actions, if necessary. This amendment also provides for optional terminating action for the repetitive inspections. This amendment is prompted by a report of a fractured frame located at body station (BS) 480. The actions specified in this AD are intended to detect and correct cracking in certain frames, which, in conjunction with multiple site cracking in the lower skin of the lap joint, could result in failure of certain lap joints, and consequent rapid decompression of the airplane fuselage.

Final rule; request for comments

2000-04-08 BOEING: Amendment 39-11590. Docket 99-NM-352-AD. \n\n\tApplicability: Model 737-200C series airplanes having line numbers 292 and subsequent, certificated in any category. \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 (e) 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.To detect and correct cracking in certain fuselage frames, which, in conjunction with multiple site cracking in the lower skin of the lap joint, could result in failure of certain lap joints, and consequent rapid decompression of the airplane fuselage, accomplish the following: \n\nRepetitive Inspections \n\n\t(a)\tPrior to the accumulation of 50,000 total flight cycles, or within 600 flight cycles after the effective date of this AD, whichever occurs later: Perform a low frequency eddy current (sliding probe) inspection to detect cracking in accordance with Part 3.A. of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1220, dated October 4, 1999. Repeat the inspections at intervals not to exceed 600 flight cycles until accomplishment of the requirements of paragraph (b) of this AD. \n\n\t(b)\tWithin 2,500 flight cycles following accomplishment of the initial inspection required by paragraph (a) of this AD: Perform an internal detailed visual inspection to detect cracking in accordance with the Part 3.B. of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1220, dated October 4, 1999. Repeat the inspection thereafter at intervals not to exceed 2,500 flight cycles until the modification required by paragraph (d) of this AD is accomplished. \n\nDetailed Visual Inspection \n\n\tNOTE 2: For the purposes of this AD, a detailed visual inspection is defined as: "An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required." \n\nCorrective Actions \n\n\t(c)\tPrior to further flight, repair any cracking detected by any inspection required by paragraph (a) or (b) of this AD 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 basis 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 approval letter must specifically reference this AD.\n\nOptional Terminating Action \n\n\t(d)\tInstallation of the preventative modification of the BS 480 frame in accordance with Part 3.C. of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1220, dated October 4, 1999, constitutes terminating action for the requirements of this AD. \n\nAlternative Methods of Compliance \n\n\t(e)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved bythe 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 3: 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\n\t(f)\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\n\t(g)\tExcept as provided by paragraph (c) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 737-53A1220, dated October 4, 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(h)\tThis amendment becomes effective on March 10, 2000.

The FAA has received a report indicating that a cracked fuselage frame was detected at body station (BS) 480, common to the stringer 5R integral shear tie stringer cutout on a Model 737-200C series airplane. Subsequent investigation revealed that the z-frame and integral-shear-tie at the stringer cutout were fractured. A crack also was detected in the S-5R and S-2R integral shear ties at the stringer cutout. A fractured frame at stringer 5R is a concern because it is adjacent to the stringer 4R lap joint, which is susceptible to multiple site cracking. Although the cracking was detected at BS 480 only, the frames at BS 500, 500A, 500B, and 520 have a similar design. Such cracking in these frames, in conjunction with multiple site cracking in the lower skin of the stringer 4R lap joint, could result in failure of the lap joint, and consequent rapid decompression of the airplane fuselage. \n\nExplanation of Relevant Service Information \n\n\tThe FAA hasreviewed and approved Boeing Alert Service Bulletin 737-53A1220, dated October 4, 1999, which describes procedures for a low frequency eddy current (LFEC) inspection to detect cracking in the lower skin at the stringer 4R lap joint between BS 460 and BS 540, and a detailed internal visual inspection to detect cracking in the frames at BS 480 through BS 520. The alert service bulletin also describes procedures for a preventative modification of the BS 480 frame. \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 Model 737-200C series airplanes of the same type design, this AD is being issued to require repetitive inspections to detect cracking in the lower skin at the stringer 4R lap joint, and certain fuselage frames; and corrective actions, if necessary. This amendment also provides for optional terminating action for the repetitive inspections. The actions are required to be accomplished inaccordance with the alert service bulletin described previously, except as discussed below. \n\nDifferences Between Service Bulletin and This AD \n\n\tOperators should note that, although the alert service bulletin does not specify repeat inspections following accomplishment of the initial internal detailed visual inspection (DVI) to detect cracking of certain frames, this AD requires that the internal DVI be repeated at intervals not to exceed 2,500 flight cycles, until accomplishment of the optional preventative modification of the BS 480 frame. The FAA finds that accomplishment of the initial inspection alone would not adequately address the unsafe condition. The FAA has determined that accomplishment of the repetitive internal DVI will maintain an adequate level of safety in the fleet until accomplishment of the preventative modification of the BS 480 frame. \n\n\tOperators also should note that, although the alert service bulletin specifies that the manufacturer may be contactedfor disposition of certain repair conditions, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings. \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.Commenters 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 99-NM-352-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, 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, 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."\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\t1. The authority citation for part 39 continues to read as follows: Authority: 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: