AD 98-20-20

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires repetitive inspections for damage or cracking of the aft pressure bulkhead, and repair, if necessary. This amendment continues to require certain repetitive inspections for damage or cracking of the aft pressure bulkhead, and repair, if necessary. This amendment removes certain repetitive inspections for cracking of the bulkhead web to Y-ring lap joint area but retains the initial inspection for cracking in that area. This amendment also adds a one-time inspection from the forward side of the bulkhead to detect fatigue cracking of the upper segment of the bulkhead web, and follow-on corrective actions, if necessary. This amendment is prompted by reports indicating that the inspections required by the existing AD may not detect cracking of the bulkhead web in a timely manner. The actions specified in this AD are intended todetect and correct fatigue cracking of the upper segment of the bulkhead web, which could result in rapid depressurization of the airplane, and consequent reduced controllability of the airplane.

Final rule; request for comments

98-20-20 BOEING: Amendment 39-10786. Docket 98-NM-257-AD. Supersedes AD 87-23-10, amendment 39-5758. \n\n\tApplicability: Model 747 series airplanes, line positions 1 through 671 inclusive; 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 (i)(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 to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo detect and correct fatigue cracking of the upper segment of the bulkhead web, which could result in rapid depressurization of the airplane, and consequent reduced controllability of the airplane, accomplish the following: \n\n\t(a)\tWithin 750 landings after December 10, 1987 (the effective date for AD 87-23-10, amendment 39-5758), unless accomplished within the last 1,250 landings (for airplanes subject to a 2,000-landing repeat inspection interval in accordance with paragraph (b) of this AD), or unless accomplished within the last 250 landings (for airplanes subject to a 1,000-landing repeat inspection interval in accordance with paragraph (b) of this AD), perform a detailed visual inspection; in accordance with Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, or Revision 5, dated January 16, 1997, or Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998; of the aft side of the entire Body Station (BS) 2360 aft pressure bulkhead for damage such as dents, tears, nicks, gouges, or scratches; and cracks at splices and doublers, and around the Auxiliary Power Unit pressure pan cutout; and, for Group 4 airplanes only, inspect from the forward side, the area adjacent to the window cutout for damage or cracks. \n\n\tNOTE 2: Notwithstanding provisions to the contrary in AD 87-23-10, and in Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, and Revision 5, dated January 16, 1997: For Model 747SR airplanes operating at a cabin pressure differential lower than 8.6 pounds-per-square-inch (psi), an adjustment factor of 1.2 shall not be used after the effective date of this AD as a multiplier for inspection thresholds andintervals specified in this AD. \n\n\t(b)\tAfter initial compliance with paragraph (a) of this AD, continue to inspect as follows: \n\n\t\t(1)\tFor Group 1 airplanes, repeat the inspections required by paragraph (a) of this AD, at intervals not to exceed 2,000 landings. \n\n\t\t(2)\tFor Groups 2 and 3 airplanes, repeat the inspections required by paragraph (a) of this AD, at intervals not to exceed 1,000 landings; or optionally, at the applicable time specified in paragraph (b)(2)(i) or (b)(2)(ii) of this AD. \n\n\t\t\t(i)\tFor Group 2 airplanes that operate the entire interval with aft lavatory complexes or galleys adjacent to bulkheads, repeat the inspections required by paragraph (a) of this AD at intervals not to exceed 2,000 landings. \n\n\t\t\t(ii)\tFor Groups 2 and 3 airplanes that operate the entire interval with an intact protective shield on the lower half of the forward side of the bulkhead, repeat the inspections required by paragraph (a) of this AD at intervals not to exceed 2,000 landings; and perform a detailed visual inspection of the protective shield for damage in accordance with Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, or Revision 5, dated January 16, 1997, or Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998, at intervals not to exceed 1,000 landings. If damage is found to the protective shield that exceeds the limits indicated in the service bulletin, prior to further flight, repeat the inspection required by paragraph (a) of this AD. \n\n\t\t(3)\tFor Group 4 airplanes, repeat the inspections required by paragraph (a) of this AD at intervals not to exceed 1,000 landings. \n\n\t(c)\tWithin 750 landings after December 10, 1987, or prior to the accumulation of 20,000 total landings, whichever occurs later, unless accomplished within the last 3,250 landings; and at intervals thereafter notto exceed 4,000 landings; perform eddy current, ultrasonic, and X-ray inspections of the aft side of the BS 2360 aft pressure bulkhead for cracks; in accordance with Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, or Revision 5, dated January 16, 1997, or Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998. \n\n\t(d)\tWithin 750 landings after December 10, 1987, or prior to the accumulation of 20,000 total landings, whichever occurs later, unless accomplished within the last 6,250 landings; and thereafter at intervals not to exceed 7,000 landings until the inspection required by paragraph (g) of this AD is accomplished: Perform a detailed visual inspection to detect cracking of the BS 2360 aft pressure bulkhead web to Y-ring lap joint area between radial stiffeners from the forward side of the bulkhead, in accordancewith Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, or Revision 5, dated January 16, 1997, or Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998. \n\n\t(e)\tIf any cracking or damage is found during any inspection required by paragraph (a), (b), (c), or (d) of this AD, repair prior to further flight in accordance with Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, or Revision 5, dated January 16, 1997, or Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998. \n\n\t(f)\tFor the purpose of complying with this AD, the number of landings may be determined to equal the number of pressurization cycles where the cabin pressure differential was greater than 2.0 psi. \n\n\t(g)\tPerform a one-time detailed visual inspection from the forward side of the bulkhead of the upper segment of the bulkhead web at BS 2360 to detect cracking, in accordance with Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998, at the earlier of the times specified in paragraphs (g)(1) and (g)(2) of this AD. If no cracking is detected during this inspection, no further action is required by this paragraph. Accomplishment of this inspection terminates the repetitive inspection requirement of paragraph (d) of this AD. \n\n\t\t(1)\tWithin 7,000 landings after the most recent detailed visual inspection accomplished in accordance with paragraph (d) of this AD. \n\n\t\t(2)\tAt the latest of the times specified in paragraphs (g)(2)(i), (g)(2)(ii), and (g)(2)(iii) of this AD.\n \n\t\t\t(i)\tPrior to the accumulation of 20,000 total landings. \n\n\t\t\t(ii)\tWithin 1,500 landings after the most recent detailed visual \t\t\tinspection accomplished in accordance with paragraph (d) of this AD. \n\n\t\t\t(iii)\tWithin 90 days after the effective date of this AD. \n\n\t(h)\tIf any cracking is detected during the inspection required by paragraph (g) of this AD, prior to further flight, accomplish a surface probe eddy current inspection from the forward side of the bulkhead to detect cracking of the upper and lower segments of the bulkhead web around the fasteners that attach the web to the outer chord of the Y-ring, in accordance with Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998. Repair any cracking, prior to further flight, 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. \n\n\t(i)\t(1)\tAn alternative method of complianceor 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(i)\t(2)\tAlternative methods of compliance for repairs and modifications, approved previously in accordance with AD 87-23-10, amendment 39-5758, are approved as alternative methods of compliance with this AD. \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\n\t(j)\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(k)\tExcept as provided by paragraph (h) of this AD, the actions shall be done in accordance with Boeing Service Bulletin 747-53-2275, dated March 26, 1987, Revision 1, dated August 13, 1987, Revision 2, dated March 31, 1988, Revision 3, dated March 29, 1990, Revision 4, dated March 26, 1992, or Revision 5, dated January 16, 1997, or Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998. These Boeing service bulletins contain the following list of effective pages: \n\n\nService Bulletin Referenced and Date\n\nPage Number\nRevision Level\nShown on Page\n Date \nShown on Page \n747-53-2275,\nMarch 26, 1987 \n1-50\nOriginal\nMarch 26, 1987 \n747-53-2275,\nRevision 1,\nAugust 13, 1987 \n1-8, 10-17,\n26-51\n\n9, 18-25\t\n1\n\n\nOriginal\nAugust 13, 1987\n\n\nMarch 26, 1987\n747-53-2275,\nRevision 2,\nMarch 31, 1988\n\n\n1-8, 10-13, 18,\n22, 29, 35, 42, \n49-53 \n\n14-17, 26-28,\n30-34, 36-41, \n43-38 \n\n9, 19-21, 23-25\n 2\n\n\n1\n\n\n\n\n Original\nMarch 31, 1988\n\n\nAugust 13, 1987 \n\n\n\n\nMarch 26, 1987 \n747-53-2275,\nRevision 3, \nMarch 29, 1990\n1-33, 35, 54-57\n\n42, 49-53\n\n34, 36-41, 43-48\n 3\n\n2\n\n1\nMarch 29, 1990\n\nMarch 31, 1988 \n\nAugust 13, 1987\n747-53-2275,\nRevision 4, \nMarch 26, 1992\n1-60\n4\nMarch 26, 1992\n747-53-2275,\nRevision 5,\nJanuary 16, 1997\n1-66\n5\nJanuary 16, 1997 \n747-53A2275,\nRevision 6, \nAugust 27, 1998\n1-76\n6\nAugust 27, 1998\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(l)\tThis amendment becomes effective on October 7, 1998.

On October 21, 1987, the FAA issued AD 87-23-10, amendment 39-5758 (52 FR 41551, October 29, 1987), applicable to certain Boeing Model 747 series airplanes, to require repetitive inspections for damage or cracking of the aft pressure bulkhead, and repair, if necessary. That action was prompted by analysis of inspection reports and the results of testing by the manufacturer. The actions required by that AD are intended to detect and correct fatigue cracking of the aft pressure bulkhead, which could result in rapid depressurization of the airplane. \n\nActions Since Issuance of Previous Rule \n\n\tSince the issuance of that AD, the FAA has received a report indicating that one operator found a 7.5-inch-long crack in the upper portion of the web of the pressure bulkhead at Body Station 2360 on a Boeing Model 747 series airplane. Analysis of the cracked bulkhead web revealed a series of short cracks initiated at the fastener holes common to the outer chord of the Y-ring in multiple locations. These cracks propagated rapidly due to fatigue, and joined together to form the 7.5-inch-long crack. \n\n\tThat airplane had accumulated 25,777 total landings and 74,266 total flight hours at the time the crack was discovered. The upper portion of the web of the pressure bulkhead of that airplane had been inspected previously in accordance with AD 87-23-10, and the crack was discovered during a repeat detailed visual inspection performed approximately 7,000 landings after the initial inspection. These findings indicate that cracking of the upper portion of the web of the pressure bulkhead could develop on the affected airplanes in fewer landings than the repetitive inspection interval of 7,000 landings that is mandated by the existing AD. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2275, Revision 6, dated August 27, 1998. That alert service bulletin describes procedures for, among other things, a detailed visual inspection performed from the forward side of the bulkhead to detect cracking of the upper segment of the bulkhead web at the attachment to the outer chord of the Y-ring. That alert service bulletin also describes procedures for follow-on corrective actions, if necessary, which include a surface probe eddy current inspection to detect cracking of the upper and lower segments of the bulkhead around the fasteners that attach the web to the outer chord of the Y-ring. The alert service bulletin also specifies that the manufacturer may be contacted for the disposition of certain repairs. \n\nExplanation 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 87-23-10 to continue to require certain repetitive inspections for damage or cracking of the aft pressure bulkhead, and repair, if necessary. In addition, this AD removes repetitive detailed visual inspections for cracking of the bulkhead web to Y-ring lap joint area but retains the initial inspection for cracking in that area. This AD also adds a one-time detailed visual inspection from the forward side of the bulkhead to detect fatigue cracking of the upper segment of the bulkhead web, and follow-on corrective actions, if necessary. The actions are required to be accomplished in accordance with the alert service bulletin described previously, except as discussed below. \n\nInterim Action \n\n\tThis is considered to be interim action. The FAA is currently considering requiring additional repetitive detailed visual inspections from the forward side of the bulkhead to detect cracking of the upper segment of the bulkhead web; repetitive surface probe high frequency eddy current inspections from the forward side of the bulkhead to detect cracking of the upper and lower segments of the bulkhead web; and repair, if necessary. However, the planned compliance time for these actions is sufficiently long so that notice and opportunity for prior public comment will be practicable. \n\nDifferences Between Alert Service Bulletin and This AD \n\n\tOperators should note that, although the alert service bulletin specifies that the manufacturer may be contacted for 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\n\tOperators also should note that the alert service bulletin specifies accomplishment of the visual inspection prior to the accumulation of 20,000 total flight cycles (landings); within 250 flight cycles after receipt of Boeing Alert Service Bulletin 747-53A2275, Revision 6; or within 1,500 flight cycles after the last visualinspection from the forward side of the bulkhead; whichever occurs latest. The FAA has determined that such compliance options may not ensure that all affected airplanes are inspected in a timely manner. \n\n\tIn developing an appropriate compliance time for this AD, the FAA considered not only the manufacturer's recommendation, but also the time necessary to accomplish the inspection (4 hours), and the average utilization of the affected fleet. The FAA finds that, due to possible variances in average utilization among airplanes, a grace period of 90 days rather than 250 flight cycles (landings) will better ensure that the inspection is accomplished on all Boeing Model 747 series airplanes in a timely manner. \n\n\tIn light of all of these factors, the FAA finds that accomplishment of the inspection for all affected airplanes prior to the accumulation of 20,000 total landings, within 1,500 landings after the last visual inspection from the forward side of the bulkhead, or within 90 days after the effective date of this AD, whichever occurs latest, represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \n\nExplanation of Applicability \n\n\tAD 87-23-10 was applicable to Boeing Model 747 series airplanes, as listed in Boeing Service Bulletin 747-53-2275, Revision 1, dated August 13, 1987. This AD is applicable to Boeing Model 747 series airplanes, line positions 1 through 671. This change is being made to more precisely define the airplanes that are affected. The line positions are the same as those referenced in the effectivity of Boeing Service Bulletin 747-53-2275, Revision 1; no new airplanes are added as a result of this change. \n\nExplanation of Disallowance of Adjustment Factor \n\n\tParagraph (g) of AD 87-23-10 specified that, based on continued mixed operation at lower cabin differential pressures, the compliance thresholds and intervals specified in that AD for Boeing Model 747 series airplanes could be multiplied by a 1.2 adjustment factor. Since the issuance of that AD, the FAA has determined that insufficient data exist to support such an adjustment to flight cycles. In fact, data are available that indicate that the use of a 1.2 adjustment factor provides inaccurate data and unjustified relief for inspection intervals. Consequently, this AD does not allow for such an adjustment factor, and the provisions of paragraph (g) of the existing AD have not been included in this AD. \n\nExplanation of Disallowance of Modification \n\n\tParagraph (j) of AD 87-23-10 specifies that modification of Boeing Model 747 series airplanes by installing certain new, improved parts would constitute terminating action for the inspection requirements of that AD. Since the issuance of AD 87-23-10, the FAA has determined that the kit necessary for accomplishment of such modification was never made available by the manufacturer. Therefore, because it is not possible to comply with the actions described by paragraph (j), the provisions of that paragraph have not been included in 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 willbe 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 98-NM-257-AD." The postcard willbe 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 \nsufficient 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 39-5758 (52 FR 41551, October 29, 1987), and by adding a new airworthiness directive (AD), amendment 39-10786, to read as follows: