AD 98-22-10

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 737 series airplanes, that currently requires repetitive inspections for cracking of the aft frame and frame support structure of the forward service doorway, and repair, if necessary. This amendment reduces the compliance time for performing the initial inspection, and reduces the repetitive inspection intervals. This amendment also adds repetitive inspections for cracking of the aft frame web of the forward service doorway, and follow-on corrective actions, if necessary. This amendment also provides for an optional terminating action for the repetitive inspection requirements of this AD. This amendment is prompted by reports indicating that the repetitive inspections required by the existing AD may not detect cracking of the aft frame and frame support structure of the forward service doorway in a timely manner. The actions specified in this AD are intended to prevent fatigue cracking of the aft frame and frame support structure of the forward service doorway, which could result in loss of the door, and consequent rapid decompression of the fuselage.

Final rule; request for comments

98-22-10 BOEING: Amendment 39-10858. Docket 98-NM-245-AD. Supersedes AD 88-03-03, amendment 39-5832. \n\n\tApplicability: Model 737 series airplanes, as listed in Boeing Service Bulletin 737-53A1108, Revision 5, dated October 26, 1989; 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 (f)(1) 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 toaddress it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent fatigue cracking of the aft frame and frame support structure of the forward service doorway, which could result in loss of the door, and consequent rapid decompression of the fuselage, accomplish the following: \n\nRESTATEMENT OF THE REQUIREMENTS OF AD 88-03-03: \n\n\t(a)\tPrior to the accumulation of 25,000 total landings or within 4,500 landings after February 28, 1988 (the effective date of AD 88-03-03, amendment 39-5832), whichever occurs later, perform an internal visual inspection for cracking in the intercostals and stringers, which support the doorstop fittings of the aft frame of the service doorway, in accordance with Boeing Service Bulletin 737-53A1108, Revision 1, dated March 12, 1987; Revision 2, dated August 13, 1987; Revision 3, dated March 3, 1988; Revision 4, dated November 17, 1988; or Revision 5, dated October 26, 1989. \n\n\t\t(1)\tIf no cracking is found during any inspection performed in accordance with paragraph (a) of this AD, repeat the inspection thereafter at intervals not to exceed 9,000 landings, until the inspection required by paragraph (b) of this AD is accomplished.\n \n\t\t(2)\tIf any cracking is found during any inspection performed in accordance with paragraph (a) of this AD, prior to further flight, repair in accordance with the service bulletin. Thereafter, repeat the inspection at intervals not to exceed 9,000 landings, until the inspection required by paragraph (b) of this AD is accomplished. \n\nNEW REQUIREMENTS OF THIS AD: \n\n\t(b)\tPerform a close visual inspection for cracking of the aft frame web and an internal visual inspection for cracking of the intercostals and stringers of the frame support structure of the forward service doorway, in accordance with Boeing Service Bulletin 737-53A1108, Revision 1, dated March 12, 1987; Revision 2, dated August 13, 1987; Revision 3, dated March 3, 1988; Revision 4, dated November 17, 1988;or Revision 5, dated October 26, 1989; at the latest of the times specified in paragraphs (b)(1), (b)(2), (b)(3), and (b)(4) of this AD. Accomplishment of these inspections constitutes terminating action for the repetitive inspection requirements of paragraphs (a)(1) and (a)(2) of this AD. \n\n\t\t(1)\tPrior to the accumulation of 18,000 total landings. \n\n\t\t(2)\tIf an internal visual inspection was performed in accordance with paragraph (b) of AD 88-03-03: Within 4,500 landings after the last inspection performed in accordance with paragraph (b) of AD 88-03-03. \n\n\t\t(3)\tWithin 700 landings after the effective date of this AD. \n\n\t\t(4)\tWithin 90 days after the effective date of this AD. \n\n\t(c)\tIf no cracking of the aft frame web, intercostals, or stringers is detected during any inspection required by paragraph (b) of this AD, repeat the inspection thereafter at intervals not to exceed 4,500 landings, until the actions specified by paragraph (e) of this AD are accomplished. \n\n\t(d)\tIf any cracking of the aft frame web, intercostals, or stringers is detected during any inspection required by paragraph (b) of this AD, prior to further flight, remove the six doorstop fittings, and perform a detailed visual inspection to detect further cracking of the frame web. Prior to further flight, repair any cracked intercostal in accordance with Figure 3 of Boeing Service Bulletin 737-53A1108, Revision 1, dated March 12, 1987; Revision 2, dated August 13, 1987; Revision 3, dated March 3, 1988; Revision 4, dated November 17, 1988; or Revision 5, dated October 26, 1989. Prior to further flight, repair any cracked frame web or stringer 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 who has been authorized by the Manager, Seattle ACO, to make such findings. Thereafter, repeat the inspection specified in paragraph (b) of this AD at intervals not to exceed 4,500 landings, until the actions specified by paragraph (e) of this AD are accomplished. \n\n\t(e)\tRepair of all intercostals in accordance with Figure 3 of Boeing Service Bulletin 737-53A1108, Revision 1, dated March 12, 1987; Revision 2, dated August 13, 1987; Revision 3, dated March 3, 1988; Revision 4, dated November 17, 1988; or Revision 5, dated October 26, 1989; or modification of all intercostals accomplished in accordance with the requirements of AD 90-06-02, amendment 39-6489; constitutes terminating action for the repetitive inspection requirements of this AD. \n\n\t(f)\t(1)\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\t(f)\t(2)\tAlternative methods of compliance pertaining to inspection methods, approved previously in accordance with AD 88-03-03, amendment 39-5832, are not considered to be approved as alternative methods of compliance with this AD. \n\n\t(f)\t(3)\tAlternative methods of compliance pertaining to repairs or modifications, approved previously in accordance with AD 88-03-03, amendment 39-5832, are considered to be approved as alternative methods of compliance with this AD. \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\n\t(g)\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\n\t(h)\tThe internal visual inspection for cracking in the intercostals and stringers, close visual inspection for cracking of the aft frame web, and repair of intercostals, if necessary, shall be done in accordance with Boeing Service Bulletin 737-53A1108, Revision 1, dated March 12, 1987; Boeing Service Bulletin 737-53A1108, Revision 2, dated August 13, 1987; Boeing Service Bulletin 737-53A1108, Revision 3, dated March 3, 1988; Boeing Service Bulletin 737-53A1108, Revision 4, dated November 17, 1988; or Boeing Service Bulletin 737-53A1108, Revision 5, dated October 26, 1989. Boeing Service Bulletin 737-53A1108, Revision 3, dated March 3, 1988, contains the following list of effective pages: \n\n\nPage Number\nShown on Page \nRevision Level\nShown on Page \nDate\nShown on Page \n1-14, 22\t\n3\nMarch 3, 1988 \n15-21, 23-27\n2\nAugust 13, 1987 \n\nThis 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(i)\tThis amendment becomes effective on November 12, 1998.

On January 11, 1988, the FAA issued AD 88-03-03, amendment 39-5832 (53 FR 1609, January 21, 1988), applicable to certain Boeing Model 737 series airplanes, to require repetitive inspections for cracking of the aft frame and frame support structure of the forward service doorway, and repair, if necessary. That action was prompted by several reports of cracks of the doorstop support structure for the doorstops on the aft frame. The actions required by that AD are intended to prevent such cracking, which could result in loss of pressurization. \n\nActions Since Issuance of Previous Rule \n\n\tSince the issuance of that AD, the FAA has received reports indicating that cracked door frames and severed intercostals of the frame support structure have been found on several Boeing Model 737 series airplanes. \n\n\tOne operator reported two airplanes with two severed intercostals on each airplane. The severed intercostals were detected during a repetitive inspectionof both airplanes that was performed in accordance with AD 88-03-03 at approximately 24,000 total landings. The same operator also reported another airplane with one severed intercostal and two additional airplanes with cracked frames. The severed intercostals were attributed to severe fatigue cracking. The initial inspection on each affected airplane was performed at approximately 18,000 total landings, and no cracking was detected during the initial inspections. \n\n\tThese findings indicate that fatigue cracking could develop on the affected airplanes at a lower number of landings than the initial inspection threshold of 25,000 total landings that is mandated by the existing AD, and that such fatigue cracking could grow from undetectable to severe in fewer landings than the repetitive inspection interval of 9,000 landings that is mandated by the existing AD. \n\n\tFatigue cracking of the aft frame and frame support structure of the forward service doorway, if not detected and corrected in a timely manner, could result in loss of the door, and consequent rapid decompression of the fuselage. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Service Bulletin 737-53A1108, Revision 5, dated October 26, 1989. That service bulletin describes procedures for a close visual inspection to detect cracking of the aft frame web of the forward service doorway around the doorstop fittings, an internal visual inspection to detect cracking of the intercostals and stringers of the frame support structure, and repair of any cracking that is detected. That service bulletin also describes a preventive modification that can be accomplished on any uncracked intercostals.\n\n Explanation of Requirements of Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of this same type design, this AD supersedes AD 88-03-03 to continue to require repetitive internal visual inspections for cracking of the frame support structure of the forward service doorway, and repair, if necessary. This AD also requires repetitive close visual inspections for cracking of the aft frame web of the forward service doorway, and follow-on corrective actions, if necessary. This AD also provides for an optional terminating action for the repetitive inspection requirements of this AD. The actions are required to be accomplished in accordance with the service bulletin described previously, except as discussed below. \n\nDifferences Between Service Bulletin and This AD \n\n\tOperators should note that, although the service bulletin describes procedures for a close visual inspection of the aft frame web of the forward service doorway around the doorstop fittings, this AD does not permit that inspection to be accomplished in lieu of the internal visual inspection. The FAA has determined that, because cracking in the frame may be masked by the doorstop fittings, the close visual inspection is not anadequate indicator of the condition of the intercostals and stringers of the frame support structure. Therefore, if any cracking is found, this AD requires removal of the doorstop fittings and a detailed visual inspection to detect further cracking of the frame, prior to the repair of any cracking. \n\n\tOperators also should note that, although the service bulletin recommends accomplishing the initial inspection prior to the accumulation of 25,000 total flight cycles (landings) or within the next 4,500 flight cycles (after receipt of the service bulletin), whichever occurs later, the FAA has determined that such a threshold does not address the identified unsafe condition in a timely manner. In addition, the FAA has determined that the repetitive inspection interval of 9,000 landings, as specified in the service bulletin, does not address the identified unsafe condition in a timely manner. The FAA's determination is based upon the case of two airplanes, described previously, on whichno cracking was detected during internal visual inspections of the intercostals at 18,000 total landings; but, during repetitive inspections conducted at approximately 24,000 total landings, two severed intercostals were found. This evidence reveals that cracking may appear earlier than 25,000 total landings and grow from being undetectable to severe in fewer than 6,000 flight cycles. In light of these factors, the FAA finds a compliance time of 18,000 total landings (or within 700 landings or 90 days after the effective date of this AD, whichever occurs later) for initiating the required inspections, and a repetitive interval of 4,500 landings, is warranted, in that those times represent an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \n\n\tOperators also should note that, although the service bulletin specifies Boeing 737 Structural Repair Manual Items (SRM) 51-40-2 and 51-40-3 as optional sources of service information for repairing cracked intercostals, this AD requires that all future repairs of cracked intercostals be accomplished in accordance with Figure 3 of the service bulletin. The FAA has determined that SRM's 51-40-2 and 51-40-3 may not provide an acceptable source of service information for repair of the intercostals. \n\n\tAdditionally, although the service bulletin specifies that SRM 53-10-4 is an appropriate source of service information for repairing cracked frames, and that SRM 53-10-3 is an appropriate source of service information for repairing cracked stringers, this AD requires that all future repairs of cracked frames or stringers be accomplished in accordance with a method approved by the FAA. The FAA has determined that SRM's 53-10-4 and 53-10-3 may not provide structurally acceptable methods of repair for frames and stringers. \n\n\tOperators should note that, although the service bulletin specifies that the manufacturer may be contacted for disposition of certain repairconditions, this proposal would require the repair of those conditions to be accomplished in accordance with a method approved by the FAA. \n\nExplanation of Revision to Applicability \n\n\tAD 88-03-03 applies to certain Boeing Model 737 series airplanes, as listed in Boeing Service Bulletin 737-53A1108, Revision 2, dated August 13, 1987. This AD is applicable to certain Boeing Model 737 series airplanes, as listed in Boeing Service Bulletin 737-53A1108, Revision 5, dated October 26, 1989. Revision 5 of the service bulletin updates the effectivity listing of the service bulletin only to reflect current airplane ownership but adds no new airplanes. \n\nOther Relevant Rulemaking \n\n\tThe FAA previously has issued AD 90-06-02, amendment 39-6489 (55 FR 8372, March 7, 1990), applicable to certain Boeing Model 737 series airplanes. That AD requires accomplishment of certain structural modifications, which constitutes terminating action for the repetitive inspection requirements of this AD. \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 thatsupports 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 98-NM-245-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted hereinwill 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." \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 removing amendment 39-5832 (53 FR 1609, January 21, 1988), and by adding a new airworthiness directive (AD), amendment 39-10858, to read as follows: