# Boeing Alert Service Bulletin 737-53A1232: Revision 4 - Rights: © The Boeing Company. Filed by the FAA in regulations.gov docket FAA-2025-3429, the docket of a proposed AD (Federal Register 2025-20061). Not covered by OpenAirDocs’ CC0 dedication. - Document: [Boeing Alert Service Bulletin 737-53A1232](https://openairdocs.org/service-documents/boeing/737-53a1232.md) - Title as filed: SB 737-53A1232 R4 -- - Pages: 154 - PDF: https://openairdocs.org/files/sha256/4d/64/4d64a26888edd00957262f407b176f22647deaee4eb030bdaa1a420695b6e559 - Page: https://openairdocs.org/service-documents/boeing/737-53a1232/file/4d64a26888ed ## Text Some pages are OCR from a scan. OCR can misread letters and numbers. Each page's text from the PDF; open the PDF at a page with #page=N. ### Page 1 Commercial Airplanes 737 Service Bulletin ALERT Number: 737-53A1232 Original Issue: April 02, 2007 Revision 4: May 22, 2024 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Chemically Milled Steps - Inspection, Repair and Preventive Modification EXPORT CONTROLLED - This technology or software is subject to the U.S. Export Administration Regulations (EAR), (15 C.F.R. Parts 730-774). No authorization from the U.S. Department of Commerce is required for export, re-export, in-country transfer, or access EXCEPT to country group E:1 or E:2 countries/persons per Supp.1 to Part 740 of the EAR. 9E991ECCN: BOEING PROPRIETARY Copyright © 2024 The Boeing Company Treatment of this document and its content is governed by contract with Boeing. Rights to use this document are licensed on a per aircraft basis and such rights may not be transferable. For more information, contact The Boeing Company. Boeing, the Boeing signature, the Boeing symbol, 707, 717, 727, 737, 747, 757, 767, 777, 787, Dreamliner, BBJ, DC-8, DC-9, DC-10, KC-10, KC-46, KDC-10, MD-10, MD-11, MD-80, MD-88, MD-90, P-8, Poseidon and Boeing liveries are all trademarks owned by The Boeing Company; and no trademark license is granted in connection with this document unless provided in writing by Boeing. Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 1 of 154 7.0 ### Page 2 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 2 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT BLANK PAGE ### Page 3 Table of Contents Revision Transmittal Sheet ............................................ 5 S u m m a r y ...................................................... 9 1. PLANNING INFORMATION ........................................ 1 3 A . E f f e c t i v i t y ............................................... 1 3 1. Airplanes ............................................ 1 3 2 . S p a r e s A f f e c t e d ........................................ 1 5 B. Concurrent Requirements ...................................... 1 5 C. Reason ................................................ 1 5 D . D e s c r i p t i o n .............................................. 1 6 E. Compliance .............................................. 1 8 F . A p p r o v a l ............................................... 2 9 G. Manpower .............................................. 3 0 H. Weight and Balance Changes .................................... 3 2 I. Electrical Load Data ......................................... 3 4 J . R e f e r e n c e s .............................................. 3 4 1. Existing Data: ......................................... 3 4 2. Data Supplied with this Service Bulletin: ........................... 3 4 3. Installation Drawings Used in the Preparation of this Service Bulletin: ........... 3 4 K. Publications Affected ........................................ 3 5 L. Interchangeability and Intermixability of Parts ........................... 3 5 M. Software Accomplishment Summary ................................ 3 5 2. MATERIAL INFORMATION ........................................ 3 7 A. Material - Price and Availability ................................... 3 7 B. Industry Support Information .................................... 3 7 C . P a r t s N e c e s s a r y f o r E a c h A i r p l a n e ................................. 3 7 1 . K i t s / P a r t s : ........................................... 3 7 2. Parts and Materials Supplied by the Operator: ........................ 3 7 3. Parts Modified and Reidentified: ............................... 3 9 4. Parts Removed and Not Replaced: .............................. 3 9 D. Parts Necessary to Change Spares ................................. 3 9 E. Special Tooling - Price and Availability ............................... 3 9 F. Special Tooling Necessary to do this Service Bulletin ....................... 3 9 3. ACCOMPLISHMENT INSTRUCTIONS .................................. 4 1 A. GENERAL INFORMATION ..................................... 4 1 B. WORK INSTRUCTIONS ....................................... 4 2 FIGURE 1: CHEM-MILLED STEP - INSPECTION [Group 1] ....................... 5 2 FIGURE 2: CHEM-MILLED STEP - INSPECTION [Group 2] ....................... 5 6 FIGURE 3: CHEM-MILLED STEP - INSPECTION [Group 3] ....................... 6 0 FIGURE 4: CHEM-MILLED STEP - INSPECTION [Group 4, Configuration 1] .............. 6 4 FIGURE 5: CHEM-MILLED STEP - INSPECTION [Group 5] ....................... 6 8 FIGURE 6: CHEM-MILLED STEP - INSPECTION [Group 6] ....................... 7 2 F I G U R E 7 : F I G U R E D E L E T E D ....................................... 7 7 F I G U R E 8 : F I G U R E D E L E T E D ....................................... 7 8 F I G U R E 9 : F I G U R E D E L E T E D ....................................... 7 9 FIGURE 10: CHEM-MILLED STEP - REPAIR - SUPPLEMENTAL INSPECTIONS ........... 8 0 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 3 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 4 FIGURE 11: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 1] ...... 8 3 FIGURE 12: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 2] ...... 9 2 FIGURE 13: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 3] ..... 1 0 1 FIGURE 14: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 4, Configuration 1 ] ................................................ 1 1 0 FIGURE 15: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 5] ..... 1 1 9 FIGURE 16: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 6] ..... 1 2 8 FIGURE 17: PREVENTATIVE MODIFICATION - POST MODIFICATION INSPECTION OF OUTER F A S T E N E R H O L E S..................................... 1 3 7 FIGURE 18: PREVENTATIVE MODIFICATION - POST MODIFICATION INSPECTION AT CHEM-MILLED S T E P ............................................. 1 3 9 FIGURE 19: CHEM-MILLED STEP - INSPECTION [Group 4, Configuration 2] ............. 1 4 1 FIGURE 20: CHEM-MILLED STEP - TYPICAL PREVENTATIVE MODIFICATION [Group 4, Configuration 2 ] ................................................ 1 4 5 APPENDIX A: AIRPLANES WITH PREVENTATIVE MODIFICATIONS INSTALLED AFTER 30,000 TOTAL F L I G H T C Y C L E S . ....................................... 1 5 4 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 4 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 5 Commercial Airplanes 737 Service Bulletin ALERT Revision Transmittal SheetNumber: 737-53A1232Original Issue: April 02, 2007 Revision 4: May 22, 2024 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Chemically Milled Steps - Inspection, Repair and Preventive Modification This revision includes all pages of the Service Bulletin. COMPLIANCE INFORMATION RELATED TO THIS REVISION Federal Aviation Administration (FAA) Airworthiness Directive AD 2017-19-26 and AD 2013-19-23 are related to this Service Bulletin. Federal Aviation Administration (FAA) Airworthiness Directive AD 2008-12-04 (superseded by AD 2017-19-26) is related to this Service Bulletin. The Federal Aviation Administration (FAA) will possibly release an additional Airworthiness Directive related to this Service Bulletin. The Airworthiness Directive will make the compliance tasks and times given in this Service Bulletin mandatory. Effects of this Revision on airplanes on which Original Issue, Revision 1, Revision 2, or Revision 3 was previously done: ActionConditionGroup Do repeat inspections at the times given in Paragraph 1.E., Compli- ance. Airplanes with permanent repairs installed in accordance with the Original Issue, Revision 1, Revision 2, or Revision 3 of this Service Bul- letin. 1, 2, 3, 4, 5, 6 Do additional actions and repeat in- spections at the times given in Paragraph 1.E., Compliance. Airplanes with time-limited repairs that were installed in accordance with the Original Issue, Revision 1, Revision 2, or Revision 3 of this Service Bulletin. 1, 2, 3, 4, 5, 6 Do repeat inspections at the new times given in Paragraph 1.E., Compliance. Airplanes that did the initial inspec- tions and have no repairs installed in accordance with the Original Is- sue, Revision 1, Revision 2, or Revi- sion 3 of this Service Bulletin. 1, 2, 3, 4, 5, 6 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 5 of 154 ### Page 6 REASON FOR REVISION This revision is sent to change the compliance times for the repeat inspections and the post-modification inspection, remove the option to install the time-limited repair, remove the permanent repair installation instructions and change the preventive modification installation instructions. Existing Service Bulletin repeat inspections are not adequate because new fleet data indicates that crack growth is faster and more distributed between tear straps, resulting in longer cracks, than originally observed in the test data that was the basis for the Service Bulletin. These sections were changed: 1. Summary - Background; updated statement to include 737-800 Boeing Converted Freighter (BCF) and operator crack finding reports, and added new Service Related Problem (SRP) reference. 2. Summary - Action; removed the permanent and time-limited repair installations. 3. Summary - Compliance; added new Airworthiness Directives (AD) and possible additional AD paragraph. 4. Summary - Manpower; added new configuration information. 5. Paragraph 1.A., Effectivity; added configurations to group 4 to include 737-800 Boeing Converted Freighter (BCF) airplanes. 6. Paragraph 1.C., Reason; updated statement to include 737-800 BCF and operator crack finding reports. Added reason for revision statement and new SRP reference. 7. Paragraph 1.D., Description; removed the permanent and time-limited repair installations. Added effects of this revision statement. 8. Paragraph 1.E., Compliance; added new ADs and possible additional AD paragraph, removed Actions to install permanent and time limited repair, included new Structural Repair Manual (SRM) reference for repair instructions. Updated table format and changed compliance times. Added footnote to clarify inspection limits for external parts. Updated PART names. 9. Paragraph 1.F., Approval; updated AMOC statement for AD 2017-19-26 and added AMOC statement for AD 2013-19-23. 10. Paragraph 1.G., Manpower; added table for new configuration and updated applicability tag. 11. Paragraph 1.H., Weight and Balance Changes; added information for new configuration. 12. Paragraph 1.J., References; added new references. 13. Paragraph 1.K., Publications Affected, changed to None. 14. Paragraph 2.C.2., Parts and Materials Supplied by the Operator; removed all parts related to permanent and time-limited repair, and added new rivets for the preventative modification, updated chemical conversion coating reference. 15. Paragraph 3.A., General Information; added notes 12 and 13. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 6 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 7 16. Paragraph 3.B., Work Instructions; removed the option to do the permanent and time-limited repair, added the SRM repair and added work instructions for 737-800 BCF airplanes. Updated the permanent repair and time-limited repair inspections. Updated PART names. Added CONDITION, OPTION and ACTION labels to match compliance table changes. Arranged work steps in PART VII to match the compliance table. 17. Figure 1, 2, 3, 4, 5, and 6; updated inspection to include an alternative Non-Destructive Testing (NDT) reference. 18. Figure 7, 8 and 9 have been deleted. 19. Figure 11, 12, 13, 14, 15, and 16; updated chemical conversion coating, rivets and overdrive instructions. 20. Figure 19; added inspection instructions for 737-800 BCF airplanes. 21. Figure 20; added modification instructions for 737-800 BCF airplanes. The data given in Alternative Method of Compliance Notice 737-53A1232AMOC02 and 737-53A1232AMOC03 are included in this revision. Vertical lines are put on the left edge of each page, except in Paragraph 1.A., Effectivity and format changes, to show the location of all content changes. Pages with no vertical lines have no changes. REVISION HISTORY April 02, 2007Original Issue: May 18, 2012Revision 1: July 26, 2013Revision 2: July 27, 2015Revision 3: May 22, 2024Revision 4: Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 7 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 8 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 8 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT BLANK PAGE ### Page 9 Commercial Airplanes 737 Service Bulletin ALERT SummaryNumber: 737-53A1232Original Issue: April 02, 2007 Revision 4: May 22, 2024 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Chemically Milled Steps - Inspection, Repair and Preventive Modification THIS DOCUMENT IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN PARAGRAPH 1.A., EFFECTIVITY. IF AN AIRPLANE HAS BEEN LEASED OR SOLD, SEND THIS DOCUMENT TO THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS DOCUMENT TO THE NEW OWNER. CONCURRENT REQUIREMENTS None. BACKGROUND During a fatigue test of a 737-800 fuselage, cracks were found in the upper skin panel at the chemically milled step above the lap joint at Stringer-4 and Stringer-10 on both the left and right sides of the airplane. A total of 56 cracks were found in Section 43 and Section 46 with the first being found after 130,000 test cycles. Metallurgical lab analysis indicates that the cracks originated after approximately 80,000 test cycles and took between 30,000 and 46,500 cycles to propagate from initiation until they broke through the thickness of the skin. The cracking at the chemically milled step is caused by fatigue stresses generated by secondary bending in the lap splice. If cracks were left undetected over a long period of time, further testing has shown that the crack tips can continue to turn and grow to the point where the skin flaps open causing a rapid decompression event. Cracking could develop at S-4 and S-10 in Sections 43 and 46 on all affected models. On 737-600 and -700 airplanes only, cracking could also develop at S-4 in Section 44. On 737-700C airplanes only, cracking could also develop at the S-7L lap splice in Section 42. On 737-800BCF airplanes, the skin from S-4R to S-24L, between STA 360 and STA 500H does not have chemically milled pockets and is not subject to chemically milled skin cracking. The S-10 splice in Section 44 has a different configuration that did not exhibit cracking during the fatigue test. Inspection of the area will ensure the structural integrity of the fuselage and installation of the preventative modification before 30,000 total flight cycles will stop cracks from occurring from normal pressurization cycles before the airplane reaches its Limit of Validity (LOV). Two operators have reported five chemically milled skin cracks just above the S-4 lap joint. The airplanes had 38,000 and 53,000 total flight cycles at the time the cracks were discovered. One of the crack reports was found before it reached the next repeat inspection in accordance with Revision 3 of this Service Bulletin, which resulted in a pressure loss event. The fuselage skin panels have been determined to be structure that is susceptible to Widespread Fatigue Damage (WFD). Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 9 of 154 ### Page 10 Boeing Service Related Problems (SRP) 737NG-SRP-53-0152, 737NG-SRP-53-0472 and 737NG-53-0626 are related to this Service Bulletin. Boeing Fleet Team Digest (FTD) 737NG-FTD-53-14002 and 737NG-FTD-53-20003 are related to this Service Bulletin. This table is provided to operators for planning purposes only. Refer to the applicable sections for more information. ReferenceAffectedPlanning Data Paragraph 1.A.2., Spares AffectedNoSpares Affected Paragraph 1.E., Compliance and Paragraph 1.F., Approval YesAD Related Paragraph 1.H., Weight and Balance ChangesYesWeight and Balance Change Paragraph 1.I., Electrical Load DataNoElectrical Load Changed Paragraph 1.K., Publications AffectedYesPublications Affected Paragraph 1.K., Publications AffectedNoAirplane Flight Operations Affected (Flight Crew Operations Manual and/or FAA Approved Air- plane Flight Manual) Paragraph 2.C.1., Kits/PartsNoKits/Parts Required Paragraph 2.C.2., Parts and Materials Supplied by the Operator YesOperator Supplied Material Paragraph 2.F., Special Tooling Necessary to do this Service Bulletin NoSpecial Tooling Required ACTION (PRR 39800-026RS) Get access to the exterior fuselage skin around S-4 and S-10 at Sections 43 and 46 on the left and right sides of the airplane on all affected models. For 737-600 and -700 airplanes only, get access to the exterior fuselage skin around S-4 at Section 44 on the left and right sides of the airplane. On 737-700C airplanes only, get access to the external fuselage skin around S-7L at Section 42. On 737-800 BCF airplanes only, get access to the external fuselage skin around S-4R, S-4L and S-10L between STA500H and STA540. Do an external Detailed inspection and an external Non Destructive Inspection (NDI) for cracking in the fuselage skin along the chemically milled step above the upper row of the lap splice. The NDI methods that can be used are Medium Frequency Eddy Current (MFEC), Magneto Optical Imaging (MOI), C-Scan or Ultrasonic Phased Array (UTPA). If any crack is found, contact The Boeing Company for repair instructions and do the repair. If no crack is found do the repeat inspections or do the preventive modification to terminate the repeat inspections. If any crack is found during a repeat inspection of a permanent repair or preventative modification, repair before further flight. EFFECTIVITY 737-600, -700, -700C, -800 and -900 series Airplane(s). Refer to Paragraph 1.A.1., Airplanes, for the list of affected airplane(s). Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 10 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 11 COMPLIANCE Federal Aviation Administration (FAA) Airworthiness Directive AD 2008-12-04 (superseded by AD 2017-19-26) is related to this Service Bulletin. The effective date of AD 2008-12-04 is July 16, 2008. Federal Aviation Administration (FAA) Airworthiness Directive AD 2017-19-26 is related to this Service Bulletin. The effective date of AD 2017-19-26 is October 30, 2017. Federal Aviation Administration (FAA) Airworthiness Directive AD 2013-19-23 is related to this Service Bulletin. The effective date of AD 2013-19-23 is November 7, 2013. The Federal Aviation Administration (FAA) will possibly release an additional Airworthiness Directive related to this Service Bulletin. The Airworthiness Directive will make the compliance tasks and times given in this Service Bulletin mandatory. Refer to Paragraph 1.E., Compliance. INDUSTRY SUPPORT INFORMATION Boeing warranty remedies are not available for the inspection, modification and repair procedures given in this Service Bulletin. MANPOWER Elapsed HoursTotal Task HoursAirplanes 5.511Group 1 and 3 6.513Group 2 12.525Group 4, Configuration 1 5.511Group 4, Configuration 2 7.515Group 5 5.2510.5Group 6 NOTE: Additional time will be required for the installation of repairs and modifications or to do post modification inspections. MATERIAL INFORMATION Operator Supplied Parts/Materials. Refer to Paragraph 2.A., Material - Price and Availability. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 11 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 12 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT INSPECT SKIN FOR CRACKS AT THE CHEMICALLY MILLED STEP, AT STRINGERS 4 AND 10, LEFT AND RIGHT * 1 000000€ THE MODIFICATION AS NECESSARY. BETWEEN STA 360 AND STA 887. DO (LEFT SIDE SHOWN, RIGHT SIDE OPPOSITE) (737-700 SHOWN, OTHER MODELS SIMILAR) FRAME TYPICAL FRAME UPPER C/L CRACK C/L SKIN S-4 S-10 C/L LOWER SKIN INSPECTION AREA TYPICAL INSPECTION AREA 483575 Original Issue: April 02, 2007 Revision 4: May 22, 2024 737-53A1232 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details 12 of 154 ### Page 13 Commercial Airplanes 737 Service Bulletin ALERT Number: 737-53A1232 Original Issue: April 02, 2007 Revision 4: May 22, 2024 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Chemically Milled Steps - Inspection, Repair and Preventive Modification THIS DOCUMENT IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN PARAGRAPH 1.A., EFFECTIVITY. IF AN AIRPLANE HAS BEEN LEASED OR SOLD, SEND THIS DOCUMENT TO THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS DOCUMENT TO THE NEW OWNER. 1. PLANNING INFORMATION A. Effectivity 1. Airplanes This bulletin is applicable to 737-600, 737-700, 737-700C, 737-800, 737-900 Airplane(s), line number(s) 1-871 in 6 Group(s). Where the effectivity is presented with hyphens between line numbers, the airplane applicability means "through" and "inclusive", e.g. line numbers 1-9 means line numbers 1 through 9 inclusive. Refer to Service Bulletin Index Document D6-19567 Part 3 for Airplane Variable Number, Line Number, and Serial Number data. This Service Bulletin is for the airplanes shown below. Refer to PRR 39800-026RS for data about this change. DESCRIPTIONCONFIGURATIONGROUP 737-600 airplanes from line number 1 thru 871.-1 737-700 airplanes from line number 1 thru 871.-2 737-700 airplanes with increased gross weight from line number 1 thru 871. -3 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 13 of 154 ### Page 14 DESCRIPTIONCONFIGURATIONGROUP 737-800 airplanes from line number 1 thru 871.-4 737-800 airplanes from line number 1 thru 871 that have not been converted to Boeing Converted Freighter (BCF) in accordance with Service Bulletin 737-00-1025. 1 737-800 airplanes from line number 1 thru 871 that have been converted to Boeing Converted Freighter (BCF) in accordance with Service Bulletin 737-00-1025. 2 737-900 airplanes from line number 1 thru 871.-5 737-700C airplanes from line number 1 thru 871.-6 Airplane Models: 737-600, 737-700, 737-700C, 737-800, 737-900 GroupVariable Number 2YA001 - YA099 2YA201 - YA210 2YA231 - YA242 2YA251 - YA254 2YA271 - YA272 2YA291 2YA301 - YA302 2YA311 - YA314 2YA321 - YA323 2YA336 - YA338 2YA501 - YA536 2YA541 - YA550 2YA571 - YA578 2YA601 - YA612 2YA621 - YA622 2YA626 - YA629 2YA681 - YA687 2YA701 - YA706 2YA721 - YA722 GroupVariable Number 2YA731 - YA734 2YA751 - YA756 2YA801 - YA803 2YA811 - YA814 2YA831 - YA834 2YA841 - YA856 2YA881 - YA882 2YA891 - YA892 2YA961 - YA966 2YB001 - YB006 2YB101 - YB103 2YB151 - YB153 2YB161 - YB162 2YB171 2YB181 2YB201 - YB202 2YB276 2YB301 2YB501 GroupVariable Number 4YC001 - YC027 4YC051 - YC068 4YC071 - YC082 4YC101 - YC104 4YC111 - YC113 4YC121 4YC126 - YC127 4YC136 - YC141 4YC146 4YC151 - YC154 4YC301 - YC303 4YC321 - YC382 4YC391 - YC392 4YC396 4YC401 - YC413 4YC416 - YC417 4YC421 4YC441 - YC447 4YC451 - YC455 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 14 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 15 GroupVariable Number 4YC459 4YC461 - YC467 4YC471 - YC485 4YC501 - YC524 4YC571 - YC581 4YC587 - YC589 4YC591 - YC593 4YC601 - YC634 4YC681 - YC696 4YC701 - YC715 4YC720 - YC723 4YC727 4YC731 - YC737 4YC751 - YC752 4YC761 - YC770 GroupVariable Number 4YC781 - YC793 4YC801 - YC865 4YC901 - YC906 4YC931 - YC932 4YC941 - YC947 4YC971 - YC973 4YC981 - YC983 4YD001 - YD005 4YD021 - YD025 4YD041 - YD051 4YD081 - YD084 4YD101 - YD106 4YD121 - YD125 4YD171 4YD201 - YD202 GroupVariable Number 4YD301 4YD401 - YD403 5YD501 - YD505 5YD531 5YD601 - YD602 1YE001 - YE020 1YE051 1YE101 - YE109 1YE151 - YE157 1YE171 - YE172 3YG001 - YG040 3YG061 - YG064 3YG066 - YG077 6YG501 - YG504 -- 2. Spares Affected None. B. Concurrent Requirements None. C. Reason During a fatigue test of a 737-800 fuselage, cracks were found in the upper skin panel at the chemically milled step above the lap joint at Stringer-4 and Stringer-10 on both the left and right sides of the airplane. A total of 56 cracks were found in Section 43 and Section 46 with the first being found after 130,000 test cycles. Metallurgical lab analysis indicates that the cracks originated after approximately 80,000 test cycles and took between 30,000 and 46,500 cycles to propagate from initiation until they broke through the thickness of the skin. The cracking at the chemically milled step is caused by fatigue stresses generated by secondary bending in the lap splice. If cracks were left undetected over a long period of time, further testing has shown that the crack tips can continue to turn and grow to the point where the skin flaps open causing a rapid decompression event. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 15 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 16 Cracking could develop at S-4 and S-10 in Sections 43 and 46 on all affected models. On 737-600 and -700 airplanes only, cracking could also develop at S-4 in Section 44. On 737-700C airplanes only, cracking could also develop at the S-7L lap splice in Section 42. On 737-800BCF airplanes, the skin from S-4R to S-24L, between STA 360 and STA 500H does not have chemically milled pockets and is not subject to chemically milled skin cracking. The S-10 splice in Section 44 has a different configuration that did not exhibit cracking during the fatigue test. Inspection of the area will ensure the structural integrity of the fuselage and installation of the preventative modification before 30,000 total flight cycles will stop cracks from occurring from normal pressurization cycles before the airplane reaches its Limit of Validity (LOV). Two operators have reported five chemically milled skin cracks just above the S-4 lap joint. The airplanes had 38,000 and 53,000 total flight cycles at the time the cracks were discovered. One of the crack reports was found before it reached the next repeat inspection in accordance with Revision 3 of this Service Bulletin, which resulted in a pressure loss event. The fuselage skin panels have been determined to be structure that is susceptible to Widespread Fatigue Damage (WFD). Boeing Service Related Problems (SRP) 737NG-SRP-53-0152, 737NG-SRP-53-0472 and 737NG-53-0626 are related to this Service Bulletin. Revision 1 was sent to add new inspection requirements to the Compliance section, Accomplishment Instructions and Figures, incorporate drawing changes and add a new figure. Revision 2 was sent to update compliance tables, correct typographical errors in the work instructions and to provide instructions for the installation of a preventive modification for short edge margin conditions. Revision 3 was sent to remove the option to install the preventative modification after 30,000 total flight cycles. Revision 4 is sent to change the compliance times for the repeat inspections and the post-modification inspection, remove the option to install the time-limited repair, remove the permanent repair installation instructions and change the preventive modification installation instructions. Existing Service Bulletin repeat inspections are not adequate because new fleet data indicates that crack growth is faster and more distributed between tear straps, resulting in longer cracks, than originally observed in the test data that was the basis for the Service Bulletin. The data given in Alternative Method of Compliance Notice 737-53A1232AMOC02 and 737-53A1232AMOC03 are included in this revision. D. Description Get access to the exterior fuselage skin around S-4 and S-10 at Sections 43 and 46 on the left and right sides of the airplane on all affected models. For 737-600 and -700 airplanes only, get access to the exterior fuselage skin around S-4 at Section 44 on the left and right sides of the airplane. On 737-700C airplanes only, get access to the external fuselage skin around S-7L at Section 42. On 737-800 BCF airplanes only, get access to the external fuselage skin around S-4R, S-4L and S-10L between STA500H and STA540. Do an external Detailed inspection and an external Non Destructive Inspection (NDI) for cracking in the fuselage skin along the chemically milled step above the upper row of the lap splice. The NDI methods that can be used are Medium Frequency Eddy Current (MFEC), Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 16 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 17 Magneto Optical Imaging (MOI), C-Scan or Ultrasonic Phased Array (UTPA). If any crack is found, contact The Boeing Company for repair instructions and do the repair. If no crack is found do the repeat inspections or do the preventive modification to terminate the repeat inspections. If any crack is found during a repeat inspection of a permanent repair or preventative modification, repair before further flight. Effects of this Issue on airplanes on which the Original Issue, Revision 1, Revision 2, or Revision 3 was previously done: ActionConditionGroup Do repeat inspections at the times given in Paragraph 1.E., Compli- ance. Airplanes with permanent repairs installed in accordance with the Original Issue, Revision 1, Revision 2, or Revision 3 of this Service Bul- letin. 1, 2, 3, 4, 5, 6 Do additional actions and repeat in- spections at the times given in Paragraph 1.E., Compliance. Airplanes with time-limited repairs that were installed in accordance with the Original Issue, Revision 1, Revision 2, or Revision 3 of this Service Bulletin. 1, 2, 3, 4, 5, 6 Do repeat inspections at the new times given in Paragraph 1.E., Compliance. Airplanes that did the initial inspec- tions and have no repairs installed in accordance with the Original Is- sue, Revision 1, Revision 2, or Revi- sion 3 of this Service Bulletin. 1, 2, 3, 4, 5, 6 The work in this service bulletin is done in the maintenance zone(s) given below. Group 1: Affected Maintenance Zones ZoneModel 221, 222, 231, 232, 241, 242737-600 Group 2-3: Affected Maintenance Zones ZoneModel 221, 222, 231, 232, 241, 242737-700 Group 4: Affected Maintenance Zones ZoneModel 221, 222, 231, 232, 241, 242737-800 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 17 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 18 Group 5: Affected Maintenance Zones ZoneModel 221, 222, 231, 232, 241, 242737-900 Group 6: Affected Maintenance Zones ZoneModel 221, 222, 231, 232, 241, 242737-700C E. Compliance Federal Aviation Administration (FAA) Airworthiness Directive AD 2008-12-04 (superseded by AD 2017-19-26) is related to this Service Bulletin. The effective date of AD 2008-12-04 is July 16, 2008. Federal Aviation Administration (FAA) Airworthiness Directive AD 2017-19-26 is related to this Service Bulletin. The effective date of AD 2017-19-26 is October 30, 2017. Federal Aviation Administration (FAA) Airworthiness Directive AD 2013-19-23 is related to this Service Bulletin. The effective date of AD 2013-19-23 is November 7, 2013. The Federal Aviation Administration (FAA) will possibly release an additional Airworthiness Directive related to this Service Bulletin. The Airworthiness Directive will make the compliance tasks and times given in this Service Bulletin mandatory. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE (6,500 feet maximum cabin altitude in lieu of 8,000 feet) as referenced in Boeing Service Bulletin 737-21-1149, the flight cycle related compliance times are different from those specified in this Service Bulletin. All initial compliance times (thresholds) specified in flight cycles must be reduced to 1/2 of those specified in this Service Bulletin. All repeat interval compliance times specified in flight cycles must be reduced to 1/4 of those specified. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST0169SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. For airplanes that have incorporated the preventative modification after 15,000 total flight cycles in accordance with the Original Issue, Revision 1, or Revision 2 of the Service Bulletin, operators must contact The Boeing Company for work instructions before 25,000 total flight cycles and do the work. All total flight cycles in the condition columns are 1/2 of those specified in this Service Bulletin. Accomplish the required action(s), based on the applicable condition(s) in Table(s) 1 through 3, in accordance with Paragraph 3. Accomplishment Instructions. When more than one OPTION is given for a CONDITION, do only one of the OPTION numbers. When more than one ACTION is given for a CONDITION or an OPTION, do all of the ACTION numbers for that CONDITION or OPTION. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 18 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 19 Table 1: Inspection Requirements of the skin at the chem-milled pockets above the lap joints at S-4, S- 10 and S-7L for airplanes without the preventative modification, time-limited repair or permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition (d)Within 600 flight cycles after the Revision 4 date of this Service Bul- letin or within 1,500 flight cycles after the last PART I inspec- tion, if the last PART I inspection done was Option 1 or within 2,100 flight cycles after the last PART I inspection, if the last PART I in- spection done was Option 2, whichever occurs first. Before 35,000 to- tal flight cycles or within 36 months after July 16, 2008, whichever occurs later. OPTION 1: Do an external Detailed inspec- tion and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Im- ager (MOI) or C-Scan inspec- tion for any crack in the fuse- lage skin at the chem-milled steps at specified locations in accordance with Accomplish- ment Instruction "PART l - IN- SPECTION". (c) AIRPLANES WITH- OUT THE PREVEN- TATIVE MODIFICA- TION, TIME-LIMITED REPAIR OR PERMA- NENT REPAIR IN- STALLED IN ACCOR- DANCE WITH THE ORIGINAL ISSUE, REVISION 1, REVI- SION 2, OR REVI- SION 3 OF THIS SERVICE BULLETIN. OPTION 2: Do an external Detailed inspec- tion and do an external Ultra- sonic Phased Array (UTPA) in- spection for any crack in the fuselage skin at the chem- milled steps at specified loca- tions in accordance with Accom- plishment Instruction "PART l - INSPECTION". (c) -Before further flight.Contact The Boeing Company for repair instructions and do the repair. CONDITION 1: ANY CRACK FOUND IN THE SKIN. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 19 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 20 Table 1: Inspection Requirements of the skin at the chem-milled pockets above the lap joints at S-4, S- 10 and S-7L for airplanes without the preventative modification, time-limited repair or permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition 600 flight cycles. (a)(b) -OPTION 1: Repeat external Detailed in- spection and external MFEC or MOI or C-Scan inspection for any crack in the fuselage skin at the chem-milled steps at specified locations in accor- dance with Accomplishment Instruction "PART l - INSPEC- TION". (a)(c) CONDITION 2: NO CRACK FOUND AS A RESULT OF OPTION 1 INSPEC- TIONS. (a)(d)Within 600 flight cycles after the most recent OPTION 1 inspection was done. OPTION 2: Do an external Detailed inspec- tion and external UTPA inspec- tion for any crack in the fuse- lage skin at the chem-milled steps at specified locations in accordance with Accomplish- ment Instruction "PART l - IN- SPECTION". (a)(c) (a)(d)Within 1,200 flight cycles after the most recent OPTION 2 inspection was done. OPTION 1: Do an external Detailed inspec- tion and external MFEC or MOI or C-Scan inspection for any crack in the fuselage skin at the chem-milled steps at specified locations in accordance with Accomplishment Instruction "PART l - INSPECTION". (a)(c) CONDITION 3: NO CRACK FOUND AS A RESULT OF OPTION 2 INSPEC- TIONS. 1,200 flight cy- cles. (a)(b) -OPTION 2: Repeat external Detailed in- spection and external UTPA inspection for any crack in the fuselage skin at the chem- milled steps at specified loca- tions in accordance with Accom- plishment Instruction "PART l - INSPECTION". (a)(c) (a) Repeat inspection is terminated when the preventative modification is installed. New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 20 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 21 Table 1: Inspection Requirements of the skin at the chem-milled pockets above the lap joints at S-4, S- 10 and S-7L for airplanes without the preventative modification, time-limited repair or permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition (b) After the accomplishment of this OPTION, it is acceptable to change the repeat action from this OPTION to any other OPTION under this CONDITION. Operators must comply with the compliance time given for the chosen OPTION under this CONDITION. (c) MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (d) Refer to the applicable CONDITION for further ACTIONS. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 21 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 22 Table 1a: Post modification inspection of the skin at the chem-milled step for airplanes with the preven- tative modification. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Within 1,200 flight cycles after the Revision 4 date of this Service Bul- letin, or within 3,200 flight cycles after the last PART VII inspec- tion was done in accordance with this Service Bul- letin, whichever occurs first. Before 50,000 to- tal flight cycles. Inspect for any crack in the fuselage skin at the chem- milled steps at the specified lo- cations in accordance with Ac- complishment Instructions "PART VII: POST PREVENTA- TIVE MODIFICATION INSPEC- TION". Airplanes with preven- tative modifications installed AT OR BE- FORE 30,000 total flight cycles. -Within 1,200 flight cycles after the Revision 4 date of this Service Bul- letin, or within 3,200 flight cycles after the last PART VII inspec- tion was done in accordance with this Service Bul- letin, whichever occurs first. Within 1,200 flight cycles after the modification dou- bler is installed. ACTION 1: Inspect for any crack in the fuselage skin at the chem- milled steps at the specified lo- cations in accordance with Ac- complishment Instructions "PART VII: POST PREVENTA- TIVE MODIFICATION INSPEC- TION". Airplanes with preven- tative modifications installed AFTER 30,000 total flight cy- cles. -Before 50,000 total flight cycles.ACTION 2: Contact The Boeing Company for work instructions and do the work. (a) -Before further flight.Contact The Boeing Company for work instructions and do the work. CONDITION 1: ANY CRACK FOUND IN THE SKIN. 1,200 flight cy- cles. -Inspect for any crack in the fuselage skin at the chem- milled steps at the specified lo- cations in accordance with Ac- complishment Instructions "PART VII: POST PREVENTA- TIVE MODIFICATION INSPEC- TION". CONDITION 2: NO CRACK FOUND IN THE SKIN. (a) Airplanes listed in APPENDIX A have been evaluated by The Boeing Company for the preventative modifications installed at the listed flight cycles. These airplanes are not required to contact The Boeing Company for work instructions only for the preventative modifications installed at the listed flight cycles. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 22 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 23 Table 1b: Post modification inspection of fasteners in the chem-milled pocket on the periphery of the preventative modification. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Within 5,500 flight cycles after the Revi- sion 4 date of this Service Bulletin or within 11,500 flight cycles after the last PART VII inspection was done in accor- dance with this Ser- vice Bulletin, whichever occurs first. Before 50,000 total flight cycles. ACTION 1: Do a High Frequency Eddy Current (HFEC) in- spection for any crack in accordance with Accom- plishment Instructions "PART VII: POST PRE- VENTATIVE MODIFICA- TION INSPECTION". AIRPLANES WITH PREVENTATIVE MODIFICATIONS IN- STALLED IN ACCOR- DANCE WITH THIS SERVICE BULLETIN. -Within 5,500 flight cycles after the Revi- sion 4 date of this Service Bulletin or within 11,500 flight cycles after the last PART VII inspection was done in accor- dance with this Ser- vice Bulletin, whichever occurs first. Before 50,000 total flight cycles. ACTION 2: Do a Detailed inspection for any crack and any loose or missing fasten- ers in accordance with Accomplishment Instruc- tions "PART VII: POST PREVENTATIVE MODI- FICATION INSPEC- TION". -Before further flight.Contact The Boeing Company for work instruc- tions and do the work. CONDITION 1: ANY CRACK FOUND IN THE SKIN. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 23 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 24 Table 1b: Post modification inspection of fasteners in the chem-milled pocket on the periphery of the preventative modification. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.ACTION 1:CONDITION 2: Replace any loose or missing fastener in accor- dance with "PART V - PREVENTATIVE MODI- FICATION". NO CRACK FOUND IN THE SKIN AND ANY LOOSE OR MISSING FASTENER FOUND. 10,000 flight cy- cles. -ACTION 2: Repeat HFEC inspection for any crack in accor- dance with Accomplish- ment Instructions "PART VII: POST PREVENTA- TIVE MODIFICATION INSPECTION". 5,500 flight cy- cles. -ACTION 3: Repeat Detailed inspec- tion for any crack and any loose or missing fas- teners in accordance with Accomplishment Instruc- tions "PART VII: POST PREVENTATIVE MODI- FICATION INSPEC- TION". 10,000 flight cy- cles. -ACTION 1: Repeat HFEC inspection for any crack in accor- dance with Accomplish- ment Instructions "PART VII: POST PREVENTA- TIVE MODIFICATION INSPECTION". CONDITION 3: NO CRACK FOUND IN THE SKIN AND NO LOOSE OR MISSING FASTENER FOUND 5,500 flight cy- cles. -ACTION 2: Repeat Detailed inspec- tion for any crack and any loose or missing fas- teners in accordance with Accomplishment Instruc- tions "PART VII: POST PREVENTATIVE MODI- FICATION INSPEC- TION". Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 24 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 25 Table 2: Inspection Requirements for airplanes with the chem-milled step Permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Within 7,300 flight cycles after the permanent repair is installed, or within 36 months after July 16, 2008, whichever occurs later. Before 50,000 to- tal flight cycles. OPTION 1 (ACTION 1): Do an external Low Frequency Eddy Current (LFEC) Inspec- tion of the skin for any crack in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". AIRPLANES WITH PERMANENT RE- PAIR INSTALLED IN ACCORDANCE WITH THE ORIGINAL ISSUE, REVISION 1, REVISION 2, OR RE- VISION 3 OF THIS SERVICE BULLETIN. -Within 7,300 flight cycles after the permanent repair is installed, or within 36 months after July 16, 2008, whichever occurs later. Before 50,000 to- tal flight cycles. OPTION 1 (ACTION 2): Doubler Inspection: Do an external LFEC Inspec- tion for any crack and an exter- nal Detailed Inspection for any crack and loose/missing fasten- ers in accordance with Accom- plishment Instructions "PART III - POST PERMANENT RE- PAIR INSPECTION". -Within 7,300 flight cycles after the permanent repair is installed, or within 36 months after July 16, 2008, whichever occurs later. Before 50,000 to- tal flight cycles. OPTION 2 (ACTION 1): Do an external LFEC Inspec- tion of the skin for any crack in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". -Within 7,300 flight cycles after the permanent repair is installed, or within 36 months after July 16, 2008, whichever occurs later. Before 50,000 to- tal flight cycles. OPTION 2 (ACTION 2): Do an internal Medium Frequen- cy Eddy Current (MFEC) In- spection of the skin for any crack in accordance with Ac- complishment Instructions "PART III - POST PERMA- NENT REPAIR INSPECTION". -Within 7,300 flight cycles after the permanent repair is installed, or within 36 months after July 16, 2008, whichever occurs later. Before 50,000 to- tal flight cycles. OPTION 2 (ACTION 3): Doubler Inspection: Do an external LFEC Inspec- tion for any crack and an exter- nal Detailed Inspection for any crack and loose/missing fasten- ers in accordance with Accom- plishment Instructions "PART III - POST PERMANENT RE- PAIR INSPECTION". Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 25 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 26 Table 2: Inspection Requirements for airplanes with the chem-milled step Permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.Contact The Boeing Company for work instructions and do the work. CONDITION 1: ANY CRACK FOUND IN THE SKIN. -Before further flight.ACTION 1:CONDITION 2: Replace any loose or missing fastener. NO CRACK FOUND IN THE SKIN AND ANY LOOSE OR MISSING FASTENER FOUND DURING OPTION 1 INSPEC- TIONS. 1,100 flight cy- cles. -ACTION 2: Repeat external Low Frequen- cy Eddy Current (LFEC) Inspec- tion of the skin for any crack in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". 4,500 flight cy- cles. -ACTION 3: Doubler Inspection: Repeat external LFEC Inspec- tion for any crack and an exter- nal Detailed Inspection for any crack and loose/missing fasten- ers in accordance with Accom- plishment Instructions "PART III - POST PERMANENT RE- PAIR INSPECTION". 1,100 flight cy- cles. -ACTION 1: Repeat external Low Frequen- cy Eddy Current (LFEC) Inspec- tion of the skin for any crack in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". CONDITION 3: NO CRACK FOUND IN THE SKIN AND NO LOOSE OR MISSING FASTENER FOUND DURING OPTION 1 INSPEC- TIONS. 4,500 flight cy- cles. -ACTION 2: Doubler Inspection: Repeat external LFEC Inspec- tion for any crack and an exter- nal Detailed Inspection for any crack and loose/missing fasten- ers in accordance with Accom- plishment Instructions "PART III - POST PERMANENT RE- PAIR INSPECTION". Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 26 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 27 Table 2: Inspection Requirements for airplanes with the chem-milled step Permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.ACTION 1:CONDITION 4: Replace any loose or missing fastener. NO CRACK FOUND IN THE SKIN AND ANY LOOSE OR MISSING FASTENER FOUND DURING OPTION 2 INSPEC- TIONS. 4,500 flight cy- cles. -ACTION 2: Repeat external LFEC Inspec- tion of the skin for any crack in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". 8,000 flight cy- cles. -ACTION 3: Repeat internal Medium Fre- quency Eddy Current (MFEC) Inspection of the skin for any crack in accordance with Ac- complishment Instructions "PART III - POST PERMA- NENT REPAIR INSPECTION". 4,500 flight cy- cles. -ACTION 4: Doubler Inspection: Repeat external LFEC Inspec- tion for any crack and an exter- nal Detailed Inspection for any crack and loose/missing fasten- ers in accordance with Accom- plishment Instructions "PART III - POST PERMANENT RE- PAIR INSPECTION". Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 27 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 28 Table 2: Inspection Requirements for airplanes with the chem-milled step Permanent repair installed. Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition 4,500 flight cy- cles. -ACTION 1: Repeat external LFEC Inspec- tion of the skin for any crack in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". CONDITION 5: NO CRACK FOUND IN THE SKIN AND NO LOOSE OR MISSING FASTENER FOUND DURING OPTION 2 INSPEC- TIONS. 8,000 flight cy- cles. -ACTION 2: Repeat internal Medium Fre- quency Eddy Current (MFEC) Inspection of the skin for any crack in accordance with Ac- complishment Instructions "PART III - POST PERMA- NENT REPAIR INSPECTION". 4,500 flight cy- cles. -ACTION 3: Doubler Inspection: Repeat external LFEC Inspection for any crack and an external De- tailed Inspection for any crack and loose/missing fasteners in accordance with Accomplish- ment Instructions "PART III - POST PERMANENT REPAIR INSPECTION". Table 3: Inspection Requirements for airplanes with a chem-milled step Time-Limited repair. Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Within 2,500 flight cy- cles after installation of the time limited re- pair or within 24 months after July 16, 2008, whichever oc- curs later. ACTION 1: Internal/External Detailed Inspection of a time limited repair for any crack and loose or missing fasteners in accordance with Accomplishment Instructions "PART IV: POST TIME LIMITED REPAIR INSPECTION". (a) AIRPLANES WITH THE TIME LIMITED REPAIR INSTALLED IN ACCORDANCE WITH THE ORIGINAL ISSUE, REVISION 1, REVISION 2, OR REVISION 3 OF THIS SERVICE BUL- LETIN. -Within 7,300 flight cy- cles after installation of the time limited re- pair or within 24 months after July 16, 2008, whichever oc- curs later. ACTION 2: Contact The Boeing Company for instructions to replace the time limit- ed repair and do the instructions. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 28 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 29 Table 3: Inspection Requirements for airplanes with a chem-milled step Time-Limited repair. Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Before further flight.Remove the time limited repair and contact The Boeing Company for repair instructions and do the repair. CONDITION 1: ANY CRACK FOUND IN THE SKIN. -Before further flight.ACTION 1:CONDITION 2: Replace any loose or missing fasten- er. NO CRACK FOUND IN THE SKIN AND ANY LOOSE OR MISSING FASTENER FOUND. 2,500 flight cy- cles. (a) -ACTION 2: Repeat Internal/External Detailed Inspection of a time limited repair for any crack and loose or missing fas- teners in accordance with Accom- plishment Instructions "PART IV: POST TIME LIMITED REPAIR IN- SPECTION". (a) 2,500 flight cy- cles. (a) -Repeat Internal/External Detailed Inspection of a time limited repair for any crack and loose or missing fas- teners in accordance with Accom- plishment Instructions "PART IV: POST TIME LIMITED REPAIR IN- SPECTION". (a) CONDITION 3: NO CRACK FOUND IN THE SKIN AND NO LOOSE OR MISSING FASTENER FOUND. (a) Repeat inspection is terminated when the permanent repair is accomplished via an approved repair by The Boeing Company Organization Designation Authorization (ODA) via a FAA Form 8100-9. F. Approval This Service Bulletin was examined by the Federal Aviation Administration (FAA). The changes specified in this Service Bulletin comply with the applicable regulations and are FAA approved, as well as European Union Aviation Safety Agency (EASA)/Joint Aviation Authorities (JAA) approved for all EASA/JAA approved airplanes listed in the Service Bulletin effectivity. This Service Bulletin and its approval were based on the airplane in its original Boeing delivery configuration or as modified by other approved Boeing changes. If an airplane has a non-Boeing modification or repair that affects a component or system also affected by this Service Bulletin, the operator is responsible for obtaining appropriate regulatory agency approval before incorporating this Service Bulletin. In addition, the Manager of the Continued Operational Safety Branch approves the accomplishment of the inspection methods, repairs, and preventative modification procedures with the corresponding compliance times specified in Tables 1, 1a, 1b, 2, and 3 under Paragraph 1.E., "Compliance", of Service Bulletin 737-53A1232, Revision 4, as an Alternative Method of Compliance (AMOC) to the accomplishment of the inspection methods, repairs, and preventative modification procedures with the Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 29 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 30 corresponding compliance times specified in Tables 1, 1a, 1b, 2, and 3, under Paragraph 1.E., "Compliance," of Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, required by paragraphs (g), (h), (i), (j), (k)(1), and (m)(1) of AD 2017-19-26. All provisions of AD 2017-19-26 that are not specifically referenced in the preceding sentence remain fully applicable and must be complied with accordingly. In addition, the Manager of the Continued Operational Safety Branch approves the incorporation of the inspection threshold, interval, and methods as given in Table 2, under Paragraph 1.E., Compliance of Service Bulletin 737-53A1232, Revision 4, as an AMOC in the area of Principal Structural Element (PSE) 53-30-04-1, 53-30-04-1a, 53-30-04-2, 53-30-04-2a, 53-30-04-3, 53-30-04-3a, 53-30-04-4, 53-30-04-4a, 53-40-03-1, 53-40-03-2, 53-60-04-1, 53-60-04-1a, 53-60-04-2, 53-60-04-2a, 53-60-04-3, 53-60-04-3a, 53-60-04-4 and 53-60-04-4a for airplanes which have not incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE (6,500 feet maximum cabin altitude in lieu of 8,000 feet) as referenced in Boeing Service Bulletin 737-21-1149, and PSE 53-30-04-1, 53-30-04-2,53-30-04-3, 53-30-04-4, 53-60-04-1, 53-60-04-2, 53-60-04-3 and 53-60-04-4 for airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE (6,500 feet maximum cabin altitude in lieu of 8,000 feet) as referenced in Boeing Service Bulletin 737-21-1149, covered by the chem-milled step permanent repair(s) only, to the incorporation of the corresponding inspections specified in Subsection B of Section 9 of Boeing Model 737-600/700/700C/800/900/900ER MPD, Document D626A001-CMR, Revision July 2011, December 2011, or August 2012, required by paragraph (g) and (h) of AD 2013-19-23. All provisions of AD 2013-19-23 that are not specifically referenced in the preceding sentence remain fully applicable and must be complied with accordingly. G. Manpower The table below shows an estimate of the task hours necessary to do the inspection only, for each airplane. Time for the repairs/preventative modifications are not given in the table below, because of the differences from airplane to airplane. Manpower requirements for repairs/preventative modifications are dependent on the quantity of repairs/preventative modifications. This estimate is for direct labor only, done by an experienced crew. Adjust the estimate with operator task-hour data if necessary. The estimate does not include lost time. These are some examples of lost time: — Time to adjust to the workplace — Time to schedule the work — Time to examine the work — Time to cure the materials — Time to make the parts — Time to find the tools. Group 1: Elapsed Hours Task HoursNumber of Persons Task 5.5112Figure 1 5.511TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 30 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 31 Group 2: Elapsed Hours Task-HoursNumber of Persons Task 6.5132Figure 2 6.513TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. Group 3: Elapsed Hours Task-HoursNumber of Persons Task 5.5112Figure 3 5.511TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. Group 4, Configuration 1: Elapsed Hours Task-HoursNumber of Persons Task 12.5252Figure 4 12.525TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. Group 4, Configuration 2: Elapsed Hours Task-HoursNumber of Persons Task 5.5112Figure 19 5.511TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 31 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 32 Group 4, Configuration 2: Elapsed Hours Task-HoursNumber of Persons Task (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. Group 5: Elapsed Hours Task-HoursNumber of Persons Task 7.5152Figure 5 7.515TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. Group 6: Elapsed Hours Task-HoursNumber of Persons Task 5.2510.52Figure 6 5.2510.5TOTAL FOR EACH AIRPLANE: (a) (b) (a) The inspection time given is for the Eddy Current inspection method. More or less time can be required for alternative inspection methods. (b) Additional time will be required for the installation of repairs and modifica- tions or to do post modification inspections. H. Weight and Balance Changes Preventative modification (Refer to Figures 11, 12, 13, 14, 15 and 16). — Change in weight = + 0.40 pounds. Permanent repair (Refer to Figure 7). — Change in weight = + 2.00 pounds. Time limited repair (Refer to Figure 8). — Change in weight = + 2.00 pounds. Permanent repair (time limited repair replacement) (Refer to Figure 9). — Change in weight = + 2.00 pounds. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 32 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 33 The Change in Moment is calculated for each preventative modification and for each Repair. These values are then summed. Refer to the following process. Group 1: 1. Measure the straight-line "X" distance in inches from the airplane's Station 360 frame to the center of the repair. The Station 360 frame is 32 inches aft of the center line of the left forward door. Add 334 inches to get the Balance Arm (BA). Multiply the BA times the weight of each repair or modification (2.00 for repair or 0.40 for modification). The product is the desired "Change in Moment". Record the value. Group 2-3, 6: 1. Measure the straight-line "X" distance in inches from the airplane's Station 360 frame to the center of the repair. The Station 360 frame is 32 inches aft of the center line of the left forward door. Add 280 inches to get the Balance Arm (BA). Multiply the BA times the weight of the repair or modification (2.00 for repair or 0.40 for modification). The product is the desired "Change in Moment". Record the value. Group 4, Configuration 1: 1. Measure the straight-line "X" distance in inches from the airplane's Station 360 frame to the center of the repair. The Station 360 frame is 32 inches aft of the center line of the left forward door. Add 162 inches to get the Balance Arm (BA). Multiply the BA times the weight of the repair or modification (2.00 for repair or 0.40 for modification). The product is the desired "Change in Moment". Record the value. Group 4, Configuration 2: 1. Measure the straight-line "X" distance in inches from the airplane's Station 360 frame to the center of the repair. The Station 360 frame is 32 inches aft of the center line of the left forward door. Add 162 inches to get the Balance Arm (BA). Multiply the BA times the weight of the repair or modification (2.00 for repair or 0.40 for modification). The product is the desired "Change in Moment". Record the value. Group 5: 1. Measure the straight-line "X" distance in inches from the airplane's Station 360 frame to the center of the repair. The Station 360 frame is 32 inches aft of the center line of the left forward door. Add 100 inches to get the Balance Arm (BA). Multiply the BA times the weight of the repair or modification (2.00 for repair or 0.40 for modification). The product is the desired "Change in Moment". Record the value. Example: A Group 2 airplane received two preventative modifications, one on each side of the airplane at "X" distance of 100 inches. The airplane also received two permanent repairs (Figure 7), one at "X" distance of 687 inches and one at "X" distance of 767 inches. What is the change in moment? Answer: (2)(100+280)(0.40) = 304 pound-inches for the two preventative modifications and (687+280)(2.00) = 1,934 pound-inches and (767+280)(2.00) = 2,094 pound-inches for the permanent repairs. Sum totals 304 + 1,934 + 2,094 = 4,332 pound-inches total effect. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 33 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 34 I. Electrical Load Data Not changed. J. References 1. Existing Data: a. Engineering Change Memo PRR 39800-026RS b. Boeing Service Bulletin 737-21-1149 c. Boeing Service Related Problem (SRP) 737NG-SRP-53-0152 , 737NG-SRP-53-042, 737NG-SRP-53-0626 d. Federal Aviation Administration (FAA) Airworthiness Directive (AD) 2008-12-04, 2013-19-23, 2017-19-26 e. Standard Overhaul Practices Manual (SOPM) 20-41-02, 20-43-03, 20-50-01, 20-50-19 f. 737 Non-Destructive Testing (NDT) Manual Part 4, 53-30-07, Part 4, 53-30-12, Part 6, 51-00-00, Part 6, 53-30-00, Part 6, 53-30-09, Part 6, 53-30-16, Part 6, 53-30-18, Part 6, 53-30-19, Part 6, 53-30-23, Part 6, 53-30-25 g. 737-600/700/800/900 Aircraft Maintenance Manual (AMM) 25-21-45, 25-21-46, 25-22-00, 25-23-61, 25-24-31, 25-56-01, 25-56-02, 25-59-01, 25-80-00 h. Fleet Team Digest (FTD) 737NG-FTD-53-14002, 737NG-FTD-53-20002 i. 737-600 Structural Repair Manual (SRM) 51-40-02. j. 737-700 Structural Repair Manual (SRM) 51-40-02. k. 737-700IGW Structural Repair Manual (SRM) 51-40-02. l. 737-700CONV Structural Repair Manual (SRM) 51-40-02. m. 737-800 Structural Repair Manual (SRM) 51-40-02. n. 737-800BCF Structural Repair Manual (SRM) 51-40-02. o. 737-900 Structural Repair Manual (SRM) 51-40-02. 2. Data Supplied with this Service Bulletin: None. 3. Installation Drawings Used in the Preparation of this Service Bulletin: TitleDrawing Number Skin-Installation - S-4L to S-4R, STA 360 to 540143A3110 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 34 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 35 TitleDrawing Number Skin-Installation - S-4 to S-10, STA 360 to 540143A3130 Skin-Installation - S-10 to S-14, STA 360 to 540143A3150 Skin-Installation - S-9L to S-9R, STA 540 to 727144A3101 Skin-Installation - S-4L to S-4R, STA 727 to 888146A3100 Skin-Installation - S-4 to S-10, STA 727 to 888146A3130 Skin-Installation - S-10 to S-14, STA 727 to 888146A3150 These drawings were used to prepare this Service Bulletin. These drawings are not necessary to make the specified changes, and are not supplied with this Service Bulletin. These drawings may not be applicable to all airplane configurations or operators. K. Publications Affected 1. Publications: None. 2. Damage Tolerance Based Structural Inspections: Boeing has evaluated the repairs and/or changes in this Service Bulletin for effects on Fatigue Critical Structure (FCS) and for changes to Damage Tolerance Inspections (DTI) required in the Maintenance Program. This Service Bulletin affects FCS. DTI requirements for the structure affected are contained in Paragraph 1.E., Compliance of this Service Bulletin. L. Interchangeability and Intermixability of Parts Accomplishment of this Service Bulletin does not affect interchangeability or intermixability of parts. M. Software Accomplishment Summary Not affected. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 35 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 36 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 36 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT BLANK PAGE ### Page 37 2. MATERIAL INFORMATION A. Material - Price and Availability The operator can supply the parts and materials shown in Paragraph 2.C., Parts Necessary For Each Airplane. As an alternative, operators can purchase the parts from Boeing Spares. This Service Bulletin does not show the Boeing price and supply data. B. Industry Support Information Boeing warranty remedies are not available for the inspection, modification and repair procedures given in this Service Bulletin. C. Parts Necessary for Each Airplane 1. Kits/Parts: None. 2. Parts and Materials Supplied by the Operator: NOTE: The parts listed below are estimate of the materials needed to accomplish a typical preventative modification in accordance with Figures 11, 12, 13, 14, 15, 16 and 20 at a single location. Fastener grip length may vary depending on the specific location of the modification. After 225,000 pressurization cycles of a fuselage fatigue test on a 737-800, a total of 56 cracks were found at different locations. The maximum number of preventative modification locations affected by this bulletin is 102 for Group 1, 122 for Group 2, 104 for Group 3, 144 for Group 4, 168 for Group 5 and 83 for Group 6. Preventative Modification NotesNameQTYPart Number / Specifica- tion (a) 0.063 inch thick. Approx- imate size 9 x 4 inches. Doubler A1A (a) 0.032 inch thick at S-4. Approximate size 9 x 4 inches. Filler B1B (a) 0.050 inch thick at S-7L. Approximate size 9 x 4 inches. (a) 0.040 inch thick at S-10. Approximate size 9 x 4 inches. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 37 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 38 Preventative Modification NotesNameQTYPart Number / Specifica- tion (a) 0.032 inch thick. Approx- imate size 11 x 5 inches. Filler C1C (a) 0.020 inch thick. Approx- imate size 9 x 6 inches. Filler D1D (i)(g)Chemical Conversion Coating 1 Ounce TYPE 1, CLASS A (b)(f)(h)Primer2 Ounce BMS 10-11, Type I (b)(h)Sealant4 Ounce BMS 5-95 Type I or II, Class B-1/2 or B-2. (c)(d)(h)Rivet24BACR15FT6D5 (c)(d)(h)Rivet16BACR15FT6D6 (c)(d)(e)(h)Rivet8BACR15DS7D7 (c)(d)(h)Rivet8BACR15GF6D (a) Fabricate from 2024-T3 clad sheet in accordance with Figures 11, 12, 13, 14, 15, 16 and 20. (b) See the Qualified Products List at the end of the Boeing Material Specification (BMS) for supplier data. (c) Refer to 737 Structural Repair Manual Chapter 51 for alternative fasteners. (d) Rivet length determined on installation. Longer rivets may be required depending on specific location. More rivet quantities may be required depending on specific location. (e) To be used if oversize fastener is necessary. (f) Some primers contain Strontium Chromate and will not be available in the European Union after January 2019 without an authorization. EU operators are encouraged to ensure their suppliers are authorized to provide the material after the sunset date and that downstream users comply with the risk mitigation measures and operational conditions. (g) Some conversion coatings contain Chromium trioxide/Chromic acid and will not be available in the European Union after September 2017 without an authorization. EU operators are encouraged to ensure their suppliers are authorized to provide the material after the sunset date and that downstream users comply with the risk mitiga- tion measures and operational conditions. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 38 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 39 Preventative Modification NotesNameQTYPart Number / Specifica- tion (h) Can be purchased from The Boeing Company. Boeing Distribution Services Inc (cage code: 2N935). 3760 W. 108th Street, Miami, FL 33018 USA Website: https://www.boeingdistribution.com Telephone: +1.305.925.2600 Fax: +1.305.507.7191 AOG: +1.305.471.8888 Email: Your BDSI customer representative or AOGdesk@Boeingdistribution.com (i) Refer to SOPM 20-43-03. 3. Parts Modified and Reidentified: None. 4. Parts Removed and Not Replaced: None. D. Parts Necessary to Change Spares None. E. Special Tooling - Price and Availability None. F. Special Tooling Necessary to do this Service Bulletin No special tools or equipment are necessary to do the change in this Service Bulletin. But, maintenance and overhaul tools in the manuals given in Paragraph 1.J., References, can be necessary. Examine operator tool supply to make sure all necessary tools are available. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 39 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 40 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 40 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT BLANK PAGE ### Page 41 3. ACCOMPLISHMENT INSTRUCTIONS A. GENERAL INFORMATION KEEP THE WORK AREA, WIRES AND ELECTRICAL BUNDLES CLEAN OF METAL PARTICLES OR CONTAMINATION WHEN YOU USE TOOLS. UNWANTED MATERIAL, METAL PARTICLES OR CONTAMINATION CAUGHT IN WIRE BUNDLES CAN CAUSE DAMAGE TO THE BUNDLES. DAMAGED WIRE BUNDLES CAN CAUSE SPARKS OR OTHER ELECTRICAL DAMAGE. CAUTION NOTE: 1. Manual titles are referred to by acronyms. Refer to Paragraph 1.J., References, for definition of the acronyms. 2. Obey all of the warnings and cautions given in the specified manual sections. 3. Unless shown differently, these dimensions and tolerances are used: – Linear dimensions are in inches – Tolerance on linear dimensions, other than rivet and bolt edge margins, is plus or minus 0.03 inch – Tolerance on rivet and bolt edge margin is plus or minus 0.05 inch – Angular tolerance is plus or minus 2 degrees – Hole dimensions for standard solid rivets and fasteners are in Structural Repair Manual (SRM) Chapter 51 – Torque Values: — Values for structural fasteners are given in 737 Structural Repair Manual, Chapter 51. 4. Use the approved fastener, process and material substitutions in accordance with SRM Chapter 51. 5. If the length of any fastener specified in this Service Bulletin does not meet installation standards given in SRM Chapter 51, then a fastener of the same specification, or an approved substitute, with a length which meets the installation standards given in SRM Chapter 51 may be used. In addition, washers may be installed for fastener grip length in accordance with SRM Chapter 51. Refer to SOPM 20-50-01 for alternate full threaded fasteners (screws) needed for installation in this Service Bulletin 6. A Detailed Inspection is defined as: An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirrors, magnifying lenses, etc. may be necessary. Surface cleaning and elaborate procedures may be required. 7. These work instructions refer to procedures included in other Boeing documents. When the words "refer to" are used and the operator has an accepted alternative procedure, the accepted alternative procedure can be used. When the words "in accordance with" are included in the instruction, the procedure in the Boeing document must be used. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 41 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 42 8. Boeing Service Letter 737-SL-51-042, Damage Reporting and Repair Plan/Design Guidelines, is an acceptable procedure to request information from Boeing for additional structural repair instructions. The Service Letter describes what information must be provided to Boeing before a structural repair can be provided. 9. If it is necessary to remove more parts for access, you can remove those parts. If you can get access without removing identified parts, it is not necessary to remove all of the identified parts. Jacking and shoring limitations must be observed. 10. Where the work instructions include installation of a kept part, a new or serviceable part with the same part number can be installed as an alternative to the kept part. 11. The compliance times for the actions in Paragraph 3.B., WORK INSTRUCTIONS are in Paragraph 1.E., Compliance. 12. An "existing external part" is defined as; a repair doubler or external butt strap. 13. When more than one OPTION is given for a CONDITION, do only one of the OPTION numbers. When more than one ACTION is given for a CONDITION or an OPTION, do all of the ACTION numbers for that CONDITION or OPTION. B. WORK INSTRUCTIONS 1. PART I: INSPECTION a. Group 1: Chem-milled pockets above the lap joints at S-4, and S-10: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 1. NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 1. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 1. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 1. NOTE: Repeat inspection is terminated when the preventative modification is installed. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 42 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 43 New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. b. Group 2: Chem-milled pockets above the lap joints at S-4, and S-10: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 2. NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 2. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 2. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 2. NOTE: Repeat inspection is terminated when the preventative modification is installed. New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. c. Group 3: Chem-milled pockets above the lap joints at S-4, and S-10: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 3. NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 3. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 43 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 44 (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 3. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 3. NOTE: Repeat inspection is terminated when the preventative modification is installed. New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. d. Group 4, Configuration 1: Chem-milled pockets above the lap joints at S-4, and S-10: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 4. NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 4. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 4. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 4. NOTE: Repeat inspection is terminated when the preventative modification is installed. New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. e. Group 5: Chem-milled pockets above the lap joints at S-4, and S-10: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 5. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 44 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 45 NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 5. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 5. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 5. NOTE: Repeat inspection is terminated when the preventative modification is installed. New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. f. Group 6: Chem-milled pockets above the lap joints at S-4, S-10 and S-7L: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 6. NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 6. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 6. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 6. NOTE: Repeat inspection is terminated when the preventative modification is installed. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 45 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 46 New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. g. Group 4, Configuration 2: Chem-milled pockets above the lap joints at S-4, and S-10: (1) OPTION 1: Do an external Detailed inspection and do an external Medium Frequency Eddy Current (MFEC) or Magneto Optic Imager (MOI) or C-Scan inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 19. NOTE: MOI and C-Scan inspections cannot be used within 4 inches of an existing external part. Within 4 inches of the edge of an existing external part, the MFEC or Ultrasonic Phased Array (UTPA) inspection must be used. (2) OPTION 2: Do an external Detailed inspection and do an external UTPA inspection for any crack in the fuselage skin at chem-milled steps in accordance with FIGURE 19. (3) CONDITION 1: If any crack is found, contact The Boeing Company for repair instructions and do the repair. (4) CONDITION 2: If no crack is found as a result of OPTION 1 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 19. (5) CONDITION 3: If no crack is found as a result of OPTION 2 inspections, do the OPTION 1 or OPTION 2 repeat inspections in accordance with FIGURE 19. NOTE: Repeat inspection is terminated when the preventative modification is installed. New installation of the preventative modification is limited to airplanes with 30,000 total flight cycles or less. For airplanes which have incorporated Boeing Business Jet Lower Cabin Altitude Supplemental Type Certificate ST01697SE, new installation of the preventative modification is limited to airplanes with 15,000 total flight cycles or less. 2. PART II: ACCESS a. Group 1-3; Group 4, Configuration 1; Group 5-6: Get internal access to the passenger cabin for the area of the skin modification or repair. (1) Remove passenger seats where necessary. Refer to 737-600/700/800/900 AMM 25-22-00 as an accepted procedure. (2) Remove sidewall linings where necessary. Refer to 737-600/700/800/900 AMM 25-21-46 as an accepted procedure. (3) Remove sidewall insulation where necessary. Refer to 737-600/700/800/900 AMM 25-80-00 as an accepted procedure. (4) Remove passenger service units where necessary. Refer to 737-600/700/800/900 AMM 25-23-61 as an accepted procedure. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 46 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 47 (5) Remove overhead stowage bins where necessary. Refer to 737-600/700/800/900 AMM 25-24-31 as an accepted procedure. (6) Remove ceiling panels where necessary. Refer to 737-600/700/800/900 AMM 25-21-45 as an accepted procedure. b. Group 4, Configuration 2: Get internal access to the cargo compartment for the area of the skin modification or repair. (1) Remove forward entry/galley door doorway sidewall lining panel, where necessary. Refer to 737-600/700/800/900 AMM 25-56-01 as an accepted procedure. (2) Remove forward lowered ceiling panels, where necessary. Refer to 737-600/700/800/900 AMM 25-56-02 as an accepted procedure. (3) Remove main deck cargo compartment lining and insulation, where necessary. 737-600/700/800/900 AMM 25-59-01 as an accepted procedure. 3. PART III: POST PERMANENT REPAIR INSPECTION a. Do the OPTIONs and ACTIONs that follows: (1) OPTION 1 (ACTION 1): Do an external Low Frequency Eddy Current (LFEC) Inspection of the skin for any crack in accordance with FIGURE 10. (2) OPTION 1 (ACTION 2): Doubler Inspection: Do an external LFEC Inspection for any crack and an external Detailed Inspection for any crack and loose/missing fasteners in accordance with FIGURE 10. (3) OPTION 2 (ACTION 1): Do an external LFEC Inspection for any crack in accordance with FIGURE 10. (4) OPTION 2 (ACTION 2): Do an internal Medium Frequency Eddy Current (MFEC) Inspection for any crack in accordance FIGURE 10. (5) OPTION 2 (ACTION 3): Doubler Inspection: Do an external LFEC Inspection for any crack and an external Detailed Inspection for any crack and loose/missing fasteners in accordance with FIGURE 10. b. CONDITION 1: If any crack is found, contact The Boeing Company for work instructions and do the work. c. CONDITION 2: If no crack found in the skin and any loose or missing fastener found during OPTION 1 inspections. (1) ACTION 1: Replace any loose or missing fastener. (2) ACTION 2: Repeat external LFEC Inspection of the skin for any crack in accordance with FIGURE 10. (3) ACTION 3: Doubler Inspection: Repeat external LFEC Inspection for any crack and an external Detailed Inspection for any crack and loose/missing fasteners in accordance with FIGURE 10. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 47 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 48 d. CONDITION 3: If no crack found in the skin and no loose or missing fastener found during OPTION 1 inspections. (1) ACTION 1: Repeat external LFEC Inspection of the skin for any crack in accordance with FIGURE 10. (2) ACTION 2: Doubler Inspection: Repeat external LFEC Inspection for any crack and an external Detailed Inspection for any crack and loose/missing fasteners in accordance with FIGURE 10. e. CONDITION 4: If no crack found in the skin and any loose or missing fastener found during OPTION 2 inspections. (1) ACTION 1: Replace any loose or missing fastener. (2) ACTION 2: Repeat external LFEC Inspection of the skin for any crack in accordance with FIGURE 10. (3) ACTION 3: Repeat internal MFEC Inspection of the skin for any crack in accordance with FIGURE 10. (4) ACTION 4: Doubler Inspection: Repeat external LFEC Inspection for any crack and external Detailed Inspection for any crack and loose/missing fasteners in accordance with FIGURE 10. f. CONDITION 5: If no crack found in the skin and no loose or missing fastener found during OPTION 2 inspections. (1) ACTION 1: Repeat external LFEC Inspection of the skin for any crack in accordance with FIGURE 10. (2) ACTION 2: Repeat internal MFEC Inspection of the skin for any crack in accordance with FIGURE 10. (3) ACTION 3: Doubler Inspection: Repeat external LFEC Inspection for any crack and external Detailed Inspection for any crack and loose/missing fasteners in accordance with FIGURE 10. 4. PART IV: POST TIME LIMITED REPAIR INSPECTION a. ACTION 1: Do an Internal and External Detailed Inspection of the repair area for any crack and loose or missing fasteners. b. ACTION 2: Contact The Boeing Company for instructions to replace the time limited repair and do the instructions. c. CONDITION 1: If any crack is found, remove the time limited repair and contact The Boeing Company for work instructions and do the work instructed by Boeing. d. CONDITION 2: If no crack is found and any missing/loose fastener found: (1) ACTION 1: Replace any loose or missing fastener. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 48 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 49 (2) ACTION 2: Repeat Internal and External Detailed Inspection of a time limited repair for any crack and loose or missing fasteners. NOTE: Repeat inspection is terminated when the permanent repair is accomplished in accordance with instructions from Boeing. e. CONDITION 3: If no crack is found and no missing/loose fastener found: (1) Repeat Internal and External Detailed Inspection of a time limited repair for any crack and loose or missing fasteners. NOTE: Repeat inspection is terminated when the permanent repair is accomplished in accordance with instructions from Boeing. 5. PART V: PREVENTATIVE MODIFICATION NOTE: Install the preventative modification prior to 30,000 total flight cycles to prevent Widespread Fatigue Damage (WFD) before the airplane reaches its limit of validity (LOV). a. Group 1-5: Install the preventative modification at S-4 and S-10 locations in accordance with the Figures in the table below: FigureGroup FIGURE 11Group 1 FIGURE 12Group 2 FIGURE 13Group 3 FIGURE 14Group 4, Configuration 1 FIGURE 20Group 4, Configuration 2 FIGURE 15Group 5 b. Group 6: Install the preventative modification at S-4, S-7L and S-10 locations in accordance with FIGURE 16. 6. PART VI: CLOSE ACCESS a. Group 1-3; Group 4, Configuration 1; Group 5-6: Install all passenger cabin equipment removed for access. (1) Install ceiling panels where necessary. Refer to 737-600/700/800/900 AMM 25-21-45 as an accepted procedure. (2) Install overhead stowage bins where necessary. Refer to 737-600/700/800/900 AMM 25-24-31 as an accepted procedure. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 49 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 50 (3) Install passenger service units where necessary. Refer to 737-600/700/800/900 AMM 25-23-61 as an accepted procedure. (4) Install sidewall insulation where necessary. Refer to 737-600/700/800/900 AMM 25-80-00 as an accepted procedure. (5) Install sidewall linings where necessary. Refer to 737-600/700/800/900 AMM 25-21-46 as an accepted procedure. (6) Install passenger seats where necessary. Refer to 737-600/700/800/900 AMM 25-22-00 as an accepted procedure. b. Group 4, Configuration 2: Install all cargo compartment equipment removed for access. (1) Install main deck cargo compartment lining and insulation, where necessary. 737-600/700/800/900 AMM 25-59-01 as an accepted procedure. (2) Install forward lowered ceiling panels, where necessary. Refer to 737-600/700/800/900 AMM 25-56-02 as an accepted procedure. (3) Install forward entry/galley door doorway sidewall lining panel, where necessary. Refer to 737-600/700/800/900 AMM 25-56-01 as an accepted procedure. c. Put the airplane back to a serviceable condition. 7. PART VII: POST PREVENTATIVE MODIFICATION INSPECTION a. Post modification inspection of the skin at the chem-milled step: (1) For airplanes with preventative modifications installed at or before 30,000 total flight cycles, do the following: (a) Do an external NDI for any crack in the fuselage skin at the chem-milled step using a MFEC inspection in accordance with FIGURE 18. (2) For airplanes with preventative modifications installed after 30,000 total flight cycles, do the following: (a) ACTION 1: Do an external NDI for any crack in the fuselage skin at the chem-milled step using a MFEC inspection in accordance with FIGURE 18. (b) ACTION 2: Contact The Boeing Company for work instructions and do the work. NOTE: Airplanes listed in APPENDIX A have been evaluated by The Boeing Company for the preventative modifications installed at the listed flight cycles. These airplanes are not required to contact The Boeing Company for work instructions only for the preventative modifications installed at the listed flight cycles. (c) CONDITION 1: If any crack is found, contact The Boeing Company for work instructions and do the work. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 50 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 51 (d) CONDITION 2: If no crack is found, repeat external NDI for any crack in the fuselage skin at the chem-milled step using a MFEC inspection in accordance with FIGURE 18. b. Post modification inspection of fasteners in the chem-milled pocket on the periphery of the preventative modification: (1) ACTION 1: Do an External High Frequency Eddy Current (HFEC) Inspection in accordance with FIGURE 17. (2) ACTION 2: Do a Detailed inspection for any crack and any loose or missing fasteners. (3) CONDITION 1: If any crack is found, contact The Boeing Company for work instructions and do the work. (4) CONDITION 2: If no crack found in the skin and any loose or missing fastener found: (a) ACTION 1: Replace any loose or missing fastener in accordance with PART V: PREVENTATIVE MODIFICATION. (b) ACTION 2: Repeat External High Frequency Eddy Current (HFEC) Inspection in accordance with FIGURE 17.. (c) ACTION 3: Repeat Detailed inspection for any crack and any loose or missing fasteners. (5) CONDITION 3: If no crack found in the skin and no loose or missing fastener found: (a) ACTION 1: Repeat External High Frequency Eddy Current (HFEC) Inspection in accordance with FIGURE 17. (b) ACTION 2: Repeat Detailed inspection for any crack and any loose or missing fasteners. Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4: May 22, 2024 51 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 52 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT This Figure applies only to: Group 1. STA 540 S-4R BL S-4L STA 360 _ S-10L 00 FOR TYPICAL SEE INSPECTION AREA AT S-4 AND S-10 LOCATIONS STA 887 _ S-4R BL /0 - S-4L STA 727 S-10L STA 00000 540 бỘỞÒ FWD C LEFT SIDE SHOWN 737-600 481398 FIGURE 1: CHEM-MILLED STEP - INSPECTION (SHEET 1 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 737-53A1232 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details 52 of 154 ### Page 53 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT STA 540 S-4L S-4R BL STA 360 S-10R _ 500 00 SEE A FOR TYPICAL INSPECTION AREA AT S-4 AND S-10 STA LOCATIONS S-4L 887 S-4R . BL STA S-10R 727 0000 0800 STA 540 100 200 FWD RIGHT SIDE SHOWN 737-600 481100 FIGURE 1: CHEM-MILLED STEP - INSPECTION (SHEET 2 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 737-53A1232 BOEING PROPRIETARY - See page 1 for details Export Controlled ECCN: 9E991 53 of 154 ### Page 54 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT FRAME TYPICAL UPPER C/L CRACK SKIN +-S OL-S ---C/L LOWER SKIN TYPICAL INSPECTION AREA • UPPER SKIN TYPICAL INSPECTION AREA CRACK LOWER STRINGER SKIN → INBD A-A 480564 FIGURE 1: CHEM-MILLED STEP - INSPECTION (SHEET 3 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 Export Controlled ECCN: 9E991 737-53A1232 BOEING PROPRIETARY - See page 1 for details 54 of 154 ### Page 55 The step numbers shown below agree with the numbers shown in the circle symbols in the figure. MORE DATAIDENTIFICATIONNAMETASKSTEP (a)(c)-SkinInspect1 (b)-SkinInspect2 (a) Do an external Non Destructive Inspection (NDI) for any crack at the chem-milled step using Option 1 or Option 2: Option 1: – Medium Frequency Eddy Current (MFEC) in accordance with 737 NDT Part 6, 53-30-09, or 737 NDT Part 6, 53-30-18 or 737 NDT Part 6, 53-30-23 or – Magneto Optic Imager (MOI) in accordance with 737 NDT Part 6, 53-30-19 or – C-Scan in accordance with 737 NDT Part 6, 53-30-25 Option 2: – Ultrasonic Phased Array (UTPA) in accordance with 737 NDT Part 4, 53-30- 07 (b) Do an external Detailed Inspection for any crack in the fuselage skin along the chem-milled steps at the specified locations. (c) A UTPA done in accordance with 737 NDT Manual Part 4, 53-30-12, is an accept- able substitute for 737 NDT Part 4, 53-30-07. FIGURE 1: CHEM-MILLED STEP - INSPECTION (SHEET 4 OF 4) Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4 May 22, 2024 55 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 56 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT This Figure applies only to: Group 2. STA 540 S-4R BL S-4L STA 360 _ S-10L •00 SEE FOR TYPICAL INSPECTION AREA AT S-4 AND S-10 LOCATIONS STA 887 _ S-4R / 0 BL - S-4L STA S-10L 727 STA 8000000 540 00 0000 FWD ' LEFT SIDE SHOWN 737-700 FIGURE 2: CHEM-MILLED STEP - INSPECTION (SHEET 1 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 737-53A1232 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details 56 of 154 ### Page 57 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT STA 540 S-4L STA S-10R 360 00 10000000009 SEE FOR TYPICAL STA AT 5-47 AND S-EA AT S-4 AND S-4L 887 LOCATIONS S-4R BL S-10R 00001 STA 540 12) FWD RIGHT SIDE SHOWN 737-700 480336 FIGURE 2: CHEM-MILLED STEP - INSPECTION (SHEET 2 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 BOEING PROPRIETARY - See page 1 for details Export Controlled ECCN: 9E991 737-53A1232 57 of 154 ### Page 58 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT FRAME TYPICAL UPPER C/L CRACK SKIN 7-S OL-S - c/L LOWER SKIN TYPICAL INSPECTION AREA • UPPER SKIN TYPICAL INSPECTION AREA CRACK LOWER STRINGER SKIN → INBD A-A 480563 FIGURE 2: CHEM-MILLED STEP - INSPECTION (SHEET 3 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 Export Controlled ECCN: 9E991 737-53A1232 BOEING PROPRIETARY - See page 1 for details 58 of 154 ### Page 59 The step numbers shown below agree with the numbers shown in the circle symbols in the figure. MORE DATAIDENTIFICATIONNAMETASKSTEP (a)(c)-SkinInspect1 (b)-SkinInspect2 (a) Do an external Non Destructive Inspection (NDI) for any crack at the chem-milled step using Option 1 or Option 2: Option 1: – Medium Frequency Eddy Current (MFEC) in accordance with 737 NDT Part 6, 53-30-09 or 737 NDT Part 6, 53-30-18 or 737 NDT Part 6, 53-30-23 or – Magneto Optic Imager (MOI) in accordance with 737 NDT Part 6, 53-30-19 or – C-Scan in accordance with 737 NDT Part 6, 53-30-25 Option 2: – Ultrasonic Phased Array (UTPA) in accordance with 737 NDT Part 4, 53-30- 07. (b) Do an external Detailed Inspection for any crack in the fuselage skin along the chem-milled steps at the specified locations. (c) A UTPA done in accordance with 737 NDT Manual Part 4, 53-30-12, is an accept- able substitute for 737 NDT Part 4, 53-30-07. FIGURE 2: CHEM-MILLED STEP - INSPECTION (SHEET 4 OF 4) Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details Original Issue: April 02, 2007 737-53A1232Revision 4 May 22, 2024 59 of 154 BOEING SERVICE BULLETIN 737-53A1232 ALERTALERT ### Page 60 (OCR) BOEING SERVICE BULLETIN 737-53A1232 ALERT ALERT This Figure applies only to: Group 3. STA 540 S-4R BL S-4L STA 360 S-10L 0000000000 FOR TYPICAL . INSPECTION AREA SEE AT S-4 AND S-10 LOCATIONS STA 887 _ S-4R / 0 BL - S-4L STA S-10L 727 00001 12 FWD LEFT SIDE SHOWN 737-700 480575 INCREASED GROSS WEIGHT FIGURE 3: CHEM-MILLED STEP - INSPECTION (SHEET 1 OF 4) Original Issue: April 02, 2007 Revision 4 May 22, 2024 737-53A1232 Export Controlled ECCN: 9E991 BOEING PROPRIETARY - See page 1 for details 60 of 154 The text continues at https://openairdocs.org/service-documents/boeing/737-53a1232/file/4d64a26888ed.md?from=61 --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). 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