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Commercial Airplanes 737 Service Bulletin ALERT Number: 737-53A1358 Original Issue: April 27, 2017 Revision 1: February 26, 2021 ATA System: 5331 SUBJECT: FUSELAGE - Skin - 0.036 Inch Crown Skin Panels Between S-10L and S-10R, STA 360 to STA 540 and STA 727 to STA 908 - Inspection, Repair and Replacement Export of this technology is controlled under the United States Export Administration Regulations (EAR) (15 CFR 300-774). An export license may be required before it is used for development, production or use by foreign persons from specific countries. The controller of this data has the individual responsibility to abide by all export laws.
9E991ECCN:
BOEING PROPRIETARY, CONFIDENTIAL AND/OR TRADE SECRET Copyright © 2017 Boeing.
Unpublished Work. All Rights Reserved.
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 27, 2017 737-53A1358Revision 1: February 26, 2021 1 of 282
4.0
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Table of Contents
Revision Transmittal Sheet7
S u m m a r y ..................................................... 1 1
1. PLANNING INFORMATION ........................................ 1 7 A . E f f e c t i v i t y ............................................... 1 7
1. Airplanes ............................................ 1 7 2 . S p a r e s A f f e c t e d ........................................ 2 4 B. Concurrent Requirements ...................................... 2 4 C. Reason ................................................ 2 4 D. Description .............................................. 2 5 E. Compliance .............................................. 2 8 F . A p p r o v a l ............................................... 3 4 G. Manpower .............................................. 3 4 H. Weight and Balance Changes .................................... 4 6 I. Electrical Load Data ......................................... 4 6 J . R e f e r e n c e s .............................................. 4 6
1. Existing Data: ......................................... 4 6
2. Data Supplied with this Service Bulletin: ........................... 4 7
3. Installation Drawings Used in the Preparation of this Service Bulletin: ........... 4 7 K. Publications Affected ........................................ 4 8 L. Interchangeability and Intermixability of Parts ........................... 4 8 M. Software Accomplishment Summary ................................ 4 8
2. MATERIAL INFORMATION ........................................ 4 9 A. Material - Price and Availability ................................... 4 9 B. Industry Support Information .................................... 7 4 C. Parts Necessary for Each Airplane ................................. 7 4 1 . K i t s / P a r t s ............................................ 7 4
2. Parts and Materials Supplied by the Operator ........................ 9 8
3. Parts Modified and Reidentified ............................... 1 0 1
4. Parts Removed and Not Replaced .............................. 1 0 1 D. Parts Necessary to Change Spares ................................ 1 0 1 E. Special Tooling - Price and Availability .............................. 1 0 1 F. Special Tooling Necessary to do this Service Bulletin ...................... 1 0 1
3. ACCOMPLISHMENT INSTRUCTIONS ................................. 1 0 3 A. GENERAL INFORMATION .................................... 1 0 3 B. WORK INSTRUCTIONS ...................................... 1 0 5 FIGURE 1: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 1-2] . . . 131 FIGURE 2: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 3-4] . . . 133 FIGURE 3: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 5] .... 1 3 5 FIGURE 4: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 6-7] . . . 137 FIGURE 5: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 8-9] . . . 139 FIGURE 6: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 10-11] . . 141 FIGURE 7: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 12] .... 1 4 3 FIGURE 8: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 13] .... 1 4 5 FIGURE 9: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 14-16] . . 147 FIGURE 10: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 17] .... 1 4 9 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.
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FIGURE 11: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 18] .... 1 5 1 FIGURE 12: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 19] .... 1 5 3 FIGURE 13: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 20] .... 1 5 5 FIGURE 14: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 21] .... 1 5 7 FIGURE 15: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 22] . . . 159 FIGURE 16: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 23] . . . 161 FIGURE 17: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 24] . . . 163 FIGURE 18: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 25] . . . 165 FIGURE 19: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 26] . . . 167 FIGURE 20: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 27] . . . 169 FIGURE 21: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 28] . . . 171 FIGURE 22: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 29-31] . . 173 FIGURE 23: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 32-34] . . 175 FIGURE 24: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 35-37] . . 177 FIGURE 25: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 38-39] . . 179 FIGURE 26: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 40] .... 1 8 1 FIGURE 27: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 540 [Group 41] .... 1 8 3 FIGURE 28: CROWN SKIN CHEM-MILL STEP INTERNAL/EXTERNAL NDI .............. 1 8 5 FIGURE 29: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 1-4] . 191 FIGURE 30: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 5] . 193 FIGURE 31: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 6-7] . 195 FIGURE 32: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 8, 10, 12-14, 1 7 - 2 1 ] ............................................. 1 9 7 FIGURE 33: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 9, 11, 16] ................................................. 1 9 9 FIGURE 34: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 15] . 201 FIGURE 35: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727G AND 908 [Group 22-28, 4 2 ] ............................................... 2 0 3 FIGURE 36: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 29-30, 3 2 - 3 3 , 3 5 , 3 8 , 4 0 - 4 1 ] ..................................... 2 0 5 FIGURE 37: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 31, 37] ................................................. 2 0 7 FIGURE 38: INSPECTION AREA FROM S-10L TO S-10R BETWEEN STA 727 AND 908 [Group 34, 36, 39] ................................................. 2 0 9 FIGURE 39: INSPECTION OF CHEM-MILL POCKETS ADJACENT TO CRACK LOCATION ..... 2 1 1 FIGURE 40: DAMAGED SKIN REMOVAL ................................. 2 1 3 FIGURE 41: CUT SURFACE AND FASTENER HOLES INSPECTION ................. 2 1 4 F I G U R E 4 2 : I N S U R A N C E C U T A N D S U R F A C E T R E A T M E N T ..................... 2 1 6 FIGURE 43: CATEGORY C REPAIR INSTALLATION .......................... 2 1 8 FIGURE 44: CATEGORY C REPAIR INSPECTION ........................... 2 2 2 FIGURE 45: PRE-REPAIR CONVERSION INSPECTION ........................ 2 2 3 FIGURE 46: OPTION 1 TO MAKE CATEGORY C REPAIR PERMANENT WITH SOLID FASTENERS AND T E A R S T R A P D O U B L E R S .................................. 2 2 4 FIGURE 47: OPTION 2 TO MAKE CATEGORY C REPAIR PERMANENT WITH A LARGER DOUBLER, S O L I D F A S T E N E R S A N D T E A R S T R A P D O U B L E R S ................... 2 3 0 FIGURE 48: POST REPAIR LFEC INSPECTION OF SERVICE BULLETIN REPAIR, OPTION 1 . . . 236 FIGURE 49: POST REPAIR LFEC INSPECTION OF SERVICE BULLETIN REPAIR, OPTION 2 . . . 238 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.
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FIGURE 50: SKIN BUTT JOINT INSPECTION AT STA 360 ....................... 2 4 0 FIGURE 51: SKIN BUTT JOINT INSPECTION AT STA 540 ....................... 2 4 2 FIGURE 52: SKIN BUTT JOINT INSPECTION AT STA 727 ....................... 2 4 4 FIGURE 53: SKIN BUTT JOINT INSPECTION AT STA 908 ....................... 2 4 6 FIGURE 54: SKIN BUTT JOINT INSPECTION AT STA 500C ...................... 2 4 8 FIGURE 55: SKIN BUTT JOINT INSPECTION AT STA 727G ...................... 2 5 0 FIGURE 56: INSPECTION AREA FROM S-10L TO S-10R FROM STA 360 TO 500C [Group 42] . . . 252 APPENDIX A: L OGIC DIAGRAM FOR TABLE 1 OF PARAGRAPH 1.E, COMPLIANCE: CROWN SKIN BONDED DOUBLER CHEM-MILL STEP - INSPECTION AND REPAIR - FROM S-10L TO S-10R - STA 360 TO STA 540 AND STA 727 TO STA 908 (GROUP 1-21, 29-41) OR STA 360 TO STA 500C AND 727G TO STA 908 (GROUP 22-28, 42) ........................ 2 5 4 APPENDIX B: LOGIC DIAGRAM FOR TABLE 2 OF PARAGRAPH 1.E, COMPLIANCE: POST REPAIR INSPECTION OF CATEGORY C REPAIR ......................... 2 5 7 APPENDIX C: LOGIC DIAGRAM FOR TABLE 3 OF PARAGRAPH 1.E, COMPLIANCE: POST REPAIR
INSPECTION OF SERVICE BULLETIN REPAIRS INSTALLED IN ACCORDANCE WITH PART 6: CHANGE CATEGORY C REPAIR TO SERVICE BULLETIN REPAIR IN THE ORIGINAL ISSUE OR ANY REVISION OF THIS SERVICE BULLETIN ................ 2 5 9 APPENDIX D: LOGIC DIAGRAM FOR TABLE 4 OF PARAGRAPH 1.E, COMPLIANCE: CROWN SKIN PANEL REPLACEMENT FROM S-10L TO S-10R - STA 360 TO STA 540 AND STA 727 TO STA 908 (GROUP 1-21, 29-41) OR STA 360 TO STA 500C AND 727G TO STA 908 (GROUP 22-28, 42) ................................................. 2 6 1 APPENDIX E: SKIN PANEL INSTALLATION DRAWINGS ......................... 2 6 2 APPENDIX F: PART DEMAND INTENT ................................... 2 8 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.
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Commercial Airplanes 737 Service Bulletin ALERT Revision Transmittal SheetNumber: 737-53A1358Original Issue: April 27, 2017 Revision 1: February 26, 2021 ATA System: 5331 SUBJECT: FUSELAGE - Skin - 0.036 Inch Crown Skin Panels Between S-10L and S-10R, STA 360 to STA 540 and STA 727 to STA 908 - Inspection, Repair and Replacement This revision includes all pages of the service bulletin.
COMPLIANCE INFORMATION RELATED TO THIS REVISION The Federal Aviation Administration (FAA) will possibly release an Airworthiness Directive related to Service Bulletin 737-53A1358 Revision 1. The Airworthiness Directive will make the compliance tasks and times given in Service Bulletin 737-53A1358 Revision 1 mandatory.
Federal Aviation Administration (FAA) Airworthiness Directive AD 2017-23-02 is related to this Service Bulletin 737-53A1358. The effective date of AD 2017-23-02 is December 20, 2017.
Airplane variable numbers PP150-PP160 and PS751-PS762 were transferred from Group 8 of service bulletin 737-53A1358 Original Issue to Group 16 of this service bulletin effectivity.
Airplane variable numbers PJ301-PJ302 PJ551-PJ551 PM551-PM564 PV021-PV055 PV201-PV203 PV271-PV272 PV281-PV283 PW028-PW028 PW033-PW050 PW052-PW054 PW064-PW068 PW072- PW072 PW094-PW094 PW101-PW102 PW106-PW106 PW118-PW120 PW156-PW157 PW161-PW167 PW201-PW244 PW261-PW261 PW265-PW268 PW278-PW278 PW281-PW281 PW293-PW293 PW296- PW296 PW301-PW327 PW461-PW461 PW463-PW467 PW504-PW504 PW564-PW564 PW614-PW620 PW661-PW662 PW681-PW683 PW701-PW701 PW711-PW717 PW741-PW742 PW761-PW761 were transferred from Group 22 of service bulletin 737-53A1358 Original Issue to new Group 42 of this service bulletin effectivity.
Effects of this Revision on airplanes on which the original issue was previously done:
ActionConditionGroup Do service bulletin 737- 53A1358 Revision 1 PART 1: CROWN SKIN CHEM- MILL STEP INTERNAL/EXTERNAL NDI.
Airplanes that have accomplished PART 1: CROWN SKIN CHEM-MILL STEP INTERNAL/EXTERNAL NDI in accordance with service bulletin 737-53A1358 original issue.
All Airplanes.
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Original Issue: April 27, 2017 737-53A1358Revision 1: February 26, 2021 7 of 282
REASON FOR REVISION This revision is sent to make changes described in the Table below:
NOTE: For all Groups the initial inspection threshold, initial repeat, initial grace period and methods remain unchanged.
ReasonGroup The original issue inspection figures show incorrect chem-mill locations.
Changes are made to some of the inspection locations.
Airplanes in Group 32, 33, 34, 36,
38.
The original issue incorrectly identified some airplanes in Group 8.
Changes are made to transfer the affected airplanes to Group 16. (a) Some of the airplanes in Group 8.
The original issue incorrectly identified some airplanes in Group 22.
Changes are made to transfer affected airplanes to new Group 42. (b) Some of the airplanes in Group 22.
The original issue inspection figures show incorrect chem-mill locations.
Changes are made to inspection locations between STA 727 and STA
908.
Airplanes in Group 5.
The original issue inspection figures show incorrect chem-mill locations.
Changes are made to inspection locations between S-4 and S-5.
Airplanes in Group 1- 42.
(a) Airplane variable numbers PP150-PP160 and PS751-PS762 were transferred from Group 8 of service bulletin 737-53A1358 Original Issue to Group 16 of this service bulletin effectivity.
(b) Airplane variable numbers PJ301-PJ302 PJ551-PJ551 PM551-PM564 PV021-PV055 PV201-PV203 PV271-PV272 PV281-PV283 PW028-PW028 PW033-PW050 PW052-PW054 PW064-PW068 PW072- PW072 PW094-PW094 PW101-PW102 PW106-PW106 PW118-PW120 PW156-PW157 PW161-PW167 PW201-PW244 PW261-PW261 PW265-PW268 PW278-PW278 PW281-PW281 PW293-PW293 PW296- PW296 PW301-PW327 PW461-PW461 PW463-PW467 PW504-PW504 PW564-PW564 PW614-PW620 PW661-PW662 PW681-PW683 PW701-PW701 PW711-PW717 PW741-PW742 PW761-PW761 were transferred from Group 22 of service bulletin 737-53A1358 Original Issue to new Group 42 of this service bulletin effectivity.
These sections were changed:
1. In Summary, Background, updated background statement and added Boeing Service Related Problem (SRP) and Boeing Fleet Team Digest (FTD).
2. In Summary, Action, added new Group 42 and Group 43.
3. In Summary, Effectivity, added airplane sub-model.
4. In Summary, Compliance, added FAA Airworthiness Directive (AD).
5. In Summary Illustration, added new Group 42.
6. In Paragraph 1.A.1., Airplanes, changed Group Configuration Table.
7. In Paragraph 1.A.1., Airplane Models, changed incorrect effectivities.
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8. In Paragraph 1.C., Reason, updated reason statement and added references to Boeing Service Related Problem (SRP) and Boeing Fleet Team Digest (FTD).
9. In Paragraph 1.D., Description, added new Group 42 and 43 and added Effects of this service bulletin Revision 1 Table.
10. In Paragraph 1.E., Compliance, added FAA Airworthiness Directive and new Group 43 and updated the Compliance Table 1.
11. In Paragraph 1.F., Approval, updated approval statement.
12. In Paragraph 1.G., Manpower, changed the incorrect bay quantity and Group information in Tables and added new Tables 46 and 47.
13. In Paragraph 1.J.1., Existing Data, added service bulletin, Boeing Service Related Problem (SRP), FAA Airworthiness Directive (AD) and Fleet Team Digest (FTD). Changed 737-100/200 Aircraft Maintenance Manual (AMM) and 737-1000/200 Structural Repair Manual (SRM) references.
14. In Paragraph 1.J.3., Installation Drawings Used in the Preparation of this service bulletin, added drawing to the Table.
15. In Paragraph 2.A., Material - Price and Availability, updated latest part numbers for Tables and added Group 42 Table.
16. In Paragraph 2.C.1., Kits/Parts, changed incorrect part number for Group 1 Table, updated latest part numbers for Group 18-21, 31 Tables and added Group 42 Table.
17. In Paragraph 2.C.2., Parts and Materials Supplied by the Operator, changed Tables.
18. In Paragraph 3.A., General Information, added new general note 21.
19. In Paragraph 3.B., Work Instructions, updated work instructions, added new Groups 42 and 43 and changed 737-100/200 Aircraft Maintenance Manual (AMM) and 737-100/200 Structural Repair Manual (SRM) references.
20. In Figures, changed Figures 1-38, 43, 46-55 and added Figure 56.
21. In Appendices, changed Appendices A, D and E.
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.
The data given in Information Notice 737-53A1358 IN01 is included in this revision.
Pages with no vertical lines have no changes.
REVISION HISTORY April 27, 2017Original Issue:
February 26, 2021Revision 1:
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Original Issue: April 27, 2017 737-53A1358Revision 1: February 26, 2021 9 of 282 BOEING SERVICE BULLETIN 737-53A1358
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Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.
Original Issue: April 27, 2017 737-53A1358Revision 1: February 26, 2021 10 of 282 BOEING SERVICE BULLETIN 737-53A1358
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Commercial Airplanes 737 Service Bulletin ALERT SummaryNumber: 737-53A1358Original Issue: April 27, 2017 Revision 1: February 26, 2021 ATA System: 5331 SUBJECT: FUSELAGE - Skin - 0.036 Inch Crown Skin Panels Between S-10L and S-10R, STA 360 to STA 540 and STA 727 to STA 908 - Inspection, Repair and Replacement
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 This service bulletin gives instructions for inspection, repair, and replacement of 0.036 inch fuselage crown skin panels where cracking at the chem-mill steps can occur between stringer (S)-10L and S-10R from station (STA) 360 to STA 540 and from STA 727 to STA 908 for 737-200/200C/300/500 airplanes and from STA 360 to STA 500C and from STA 727G to STA 908 for 737-400 airplanes. On these skin panels, the bonded doubler is chemically milled to create pockets. At these locations, the loads could cause a condition where cracks could form along the longitudinal edges of the doubler at the step of the chem-mill pockets. The inspection, in accordance with this service bulletin, will allow early detection of cracks in the crown skin panels and prevent Widespread Fatigue Damage (WFD) by reducing the chance of multiple adjacent chem-mill step cracks from linking with each other. The repair of cracks in accordance with this service bulletin will restore the structural integrity of the skin panel. If the skin cracks propagate without detection, they could adversely affect the structural integrity of the airplane.
An operator of a 737-300 airplane reported multiple chem-mill step cracks in adjacent bays of the fuselage crown skin. These cracks were discovered by visual inspection only 855 flight cycles after the last detailed inspection in accordance with Boeing Alert Service Bulletin (SB) 737-53A1210. The initial visual inspection revealed three cracks varying in length from 1.8 inches to 8.5 inches. Further inspection using Ultrasonic Phased Array revealed nine additional sub-surface cracks. The airplane had 55,232 flight cycles.
Boeing Service Related Problem (SRP) 737-SRP-53-0517 and 737-SRP-53-0607 are related to this service bulletin.
Boeing Fleet Team Digest (FTD) 737 FTD 53-15007 and 737 FTD 53-19002 are related to this service bulletin.
The fuselage crown skin has been determined to be structure that is susceptible to WFD.
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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 AffectedNoPublications 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/PartsYesKits/Parts Required Paragraph 2.C.2., Parts and Materials Supplied by the Operator YesOperator Supplied Parts/Material Paragraph 2.F., Special Tooling Necessary to do this Service Bulletin NoSpecial Tooling Required ACTION Classification of repairs in this service bulletin
DESCRIPTIONREPAIR TYPE A Category B repair for which supplemental inspections are necessary at the specified threshold and repeat intervals in accordance with the Structural Repair Manual (SRM).
SRM Repair A Category C repair that has been changed to a Category B repair for which supplemental inspections are necessary at the specified threshold and repeat intervals in accordance with this Service Bulletin (SB).
Service Bulletin Repair A time-limited repair which must be replaced or reworked within a specified time limit. Also supplemental inspections are necessary at a specified threshold and repeat interval in accordance with this service bulletin.
Category C Group 1-21, 29-41:
Do a Non-Destructive Inspection (NDI) for any crack of the crown skin adjacent to the chem-mill steps in the area from S-10L to S-10R, from STA 360 to STA 540 and from STA 727 to STA 908. If any crack is found, install a SRM Repair or install a Category C Repair and repeat the external NDI of the crown skin for any crack. If no crack is found, repeat the NDI inspections for any crack.
Group 22-28, 42:
Do a Non-Destructive Inspection (NDI) for any crack of the crown skin adjacent to the chem-mill steps in the area from S-10L to S-10R, from STA 360 to STA 500C and from STA 727G to STA 908. If any crack is found, install a SRM Repair or install a Category C Repair and repeat the external NDI of the crown skin for any crack.
If no crack is found, repeat the NDI inspections for any crack.
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Original Issue: April 27, 2017 737-53A1358Revision 1: February 26, 2021 12 of 282 BOEING SERVICE BULLETIN 737-53A1358