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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
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Table of Contents
Revision Transmittal Sheet5
S u m m a r y9
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
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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
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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., Compliance.
Airplanes with permanent repairs 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 additional actions and repeat inspections 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 inspections and have no repairs installed in accordance with the Original Issue, Revision 1, Revision 2, or Revision 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
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.
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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:
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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).
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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 Airplane 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).
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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.
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BOEING SERVICE BULLETIN 737-53A1232
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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