Boeing ASB 737-57A1269: Revision 2, text

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Commercial Airplanes 737 Service Bulletin ALERT Number: 737-57A1269 Original Issue: December 04, 2003 Revision 2: October 11, 2018 ATA System: 5712 SUBJECT: WINGS - Wing Center Section Rear Spar - Replacement of Stiffeners at Left and Right BBL 6.15 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:

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.

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Original Issue: December 04, 2003 737-57A1269Revision 2: October 11, 2018 2 of 241 BOEING SERVICE BULLETIN 737-57A1269

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Table of Contents

Revision Transmittal Sheet7

S u m m a r y ..................................................... 1 1

1. PLANNING INFORMATION ........................................ 1 5 A . E f f e c t i v i t y ............................................... 1 5

1. Airplanes ............................................ 1 5 2 . S p a r e s A f f e c t e d ........................................ 3 3 B. Concurrent Requirements ...................................... 3 3 C. Reason ................................................ 3 3 D. Description .............................................. 3 5 E. Compliance .............................................. 3 7 F . A p p r o v a l ............................................... 3 8 G. Manpower .............................................. 3 9 H. Weight and Balance Changes .................................... 4 0 I. Electrical Load Data ......................................... 4 0 J . R e f e r e n c e s .............................................. 4 0

1. Existing Data: ......................................... 4 0

2. Data Supplied with this Service Bulletin: ........................... 4 1

3. Installation Drawings Used in the Preparation of this Service Bulletin: ........... 4 1 K. Publications Affected ........................................ 4 1 L. Interchangeability and Intermixability of Parts ........................... 4 1 M. Software Accomplishment Summary ................................ 4 1

2. MATERIAL INFORMATION ........................................ 4 3 A. Material - Price and Availability ................................... 4 3 B. Industry Support Information .................................... 4 4 C. Parts Necessary for Each Airplane ................................. 4 5 1 . K i t s / P a r t s : ........................................... 4 5

2. Parts and Materials Supplied by the Operator: ........................ 5 3

3. Parts Modified and Reidentified: ............................... 5 4

4. Parts Removed and Not Replaced: .............................. 5 4 D. Parts Necessary to Change Spares ................................. 5 4 E. Special Tooling - Price and Availability ............................... 5 5 F. Special Tooling Necessary to do this Service Bulletin ....................... 5 5

3. ACCOMPLISHMENT INSTRUCTIONS .................................. 5 7 A. GENERAL INFORMATION ..................................... 5 7 B. WORK INSTRUCTIONS ....................................... 5 8 F I G U R E 1 : T H I S F I G U R E I S D E L E T E D .................................. 6 6 FIGURE 2: LEFT SIDE BRACKET REMOVALS [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3;

Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] .................. 6 7 FIGURE 3: RIGHT SIDE BRACKET REMOVALS [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] ................. 7 1 FIGURE 4: ANGLE REMOVAL [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .................. 7 6 FIGURE 5: LEFT SIDE BRACKET REMOVALS [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .......................... 7 8 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.

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FIGURE 6: RIGHT SIDE BRACKET REMOVALS [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .......................... 8 2 FIGURE 7: STIFFENER REMOVAL - LBL 6.15 [Group 1, Configuration 1, 3] .............. 8 7 FIGURE 8: STIFFENER REMOVAL - LBL 6.15 [Group 3, Configuration 1, 3; Group 5, Configuration 1, 3] .................................................. 8 9 FIGURE 9: STIFFENER REMOVAL - LBL 6.15 [Group 4, Configuration 1, 3] .............. 9 1 FIGURE 10: STIFFENER REMOVAL - LBL 6.15 [Group 6, Configuration 1, 3; Group 7, Configuration 1, 3;

Group 8, Configuration 1, 3] .................................. 9 3 FIGURE 11: GUSSET AND GROMMET REMOVAL - LBL 6.15 [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] . 95 FIGURE 12: NUTPLATE INSTALLATION - LBL 6.15 [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] ................. 9 7 FIGURE 13: HOLE LOCATIONS AND GROUND STUD INSTALLATION - LBL 6.15 [Group 6, Configuration 1 , 3 , 5 - 6 ] ............................................ 1 0 0 FIGURE 14: HOLE LOCATIONS AND GROUND STUD INSTALLATION - LBL 6.15 [Group 7, Configuration 1 , 3 , 5 - 6 ] ............................................ 1 0 3 FIGURE 15: HOLE LOCATIONS AND GROUND STUD INSTALLATION - LBL 6.15 [Group 8, Configuration 1 , 3 , 5 - 6 ] ............................................ 1 0 6 FIGURE 16: STIFFENER PRE-INSTALLATION - LBL 6.15 [Group 1, Configuration 1, 3] ....... 1 0 9 FIGURE 17: STIFFENER PRE-INSTALLATION - LBL 6.15 [Group 3, Configuration 1, 3; Group 5, Configuration 1 , 3 ] .............................................. 1 1 2 FIGURE 18: STIFFENER PRE-INSTALLATION - LBL 6.15 [Group 4, Configuration 1, 3] ....... 1 1 5 FIGURE 19: STIFFENER PRE-INSTALLATION - LBL 6.15 [Group 6, Configuration 1, 3; Group 7, Configuration 1, 3; Group 8, Configuration 1, 3] ............................... 1 1 8 FIGURE 20: STIFFENER INSTALLATION - LBL 6.15 [Group 1, Configuration 1, 3] .......... 1 2 1 F I G U R E 2 1 : T H I S F I G U R E I S D E L E T E D ................................. 1 2 4 FIGURE 22: STIFFENER INSTALLATION - LBL 6.15 [Group 3, Configuration 1, 3; Group 5, Configuration 1 , 3 ] .............................................. 1 2 5 FIGURE 23: STIFFENER INSTALLATION - LBL 6.15 [Group 4, Configuration 1, 3] .......... 1 2 8 FIGURE 24: STIFFENER INSTALLATION - LBL 6.15 [Group 6, Configuration 1, 3; Group 7, Configuration 1, 3; Group 8, Configuration 1, 3] ............................... 1 3 1 FIGURE 25: GUSSET AND GROMMET INSTALLATION - LBL 6.15 [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] . 134 FIGURE 26: STIFFENER REMOVAL - RBL 6.15 [Group 1, Configuration 1, 3] ............. 1 3 7 FIGURE 27: STIFFENER REMOVAL - RBL 6.15 [Group 3, Configuration 1, 3] ............. 1 3 9 FIGURE 28: STIFFENER REMOVAL - RBL 6.15 [Group 4, Configuration 1, 3] ............. 1 4 1 FIGURE 29: STIFFENER REMOVAL - RBL 6.15 [Group 5, Configuration 1, 3] ............. 1 4 3 FIGURE 30: STIFFENER REMOVAL - RBL 6.15 [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .......................... 1 4 5 FIGURE 31: GUSSET REMOVAL - RBL 6.15 [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .................. 1 4 7 FIGURE 32: HOLE LOCATIONS AND GROUND STUD INSTALLATION - RBL 6.15 [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] . 149 FIGURE 33: HOLE LOCATIONS - RBL 6.15 [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] ............................ 1 5 1 FIGURE 34: STIFFENER PRE-INSTALLATION - RBL 6.15 [Group 1, Configuration 1, 3] ....... 1 5 3 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.

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FIGURE 35: STIFFENER PRE-INSTALLATION - RBL 6.15 [Group 3, Configuration 1, 3] ....... 1 5 6 FIGURE 36: STIFFENER PRE-INSTALLATION - RBL 6.15 [Group 4, Configuration 1, 3] ....... 1 5 9 FIGURE 37: STIFFENER PRE-INSTALLATION - RBL 6.15 [Group 5, Configuration 1, 3] ....... 1 6 2 FIGURE 38: STIFFENER PRE-INSTALLATION - RBL 6.15 [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .................. 1 6 5 FIGURE 39: STIFFENER INSTALLATION - RBL 6.15 [Group 1, Configuration 1, 3] .......... 1 6 8 F I G U R E 4 0 : T H I S F I G U R E I S D E L E T E D ................................. 1 7 1 FIGURE 41: STIFFENER INSTALLATION - RBL 6.15 [Group 3, Configuration 1, 3] .......... 1 7 2 FIGURE 42: STIFFENER INSTALLATION - RBL 6.15 [Group 4, Configuration 1, 3] .......... 1 7 5 FIGURE 43: STIFFENER INSTALLATION - RBL 6.15 [Group 5, Configuration 1, 3] .......... 1 7 8 FIGURE 44: STIFFENER INSTALLATION - RBL 6.15 [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .......................... 1 8 1 FIGURE 45: GUSSET INSTALLATION - RBL 6.15 [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3, 5-6;

Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] ............. 1 8 4 FIGURE 46: LEFT SIDE BRACKET INSTALLATIONS [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] ............... 1 8 7 FIGURE 47: RIGHT SIDE BRACKET INSTALLATIONS [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] ............... 1 9 1 FIGURE 48: ANGLE INSTALLATION [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3; Group 7, Configuration 1, 3; Group 8, Configuration 1, 3] ....................... 1 9 7 FIGURE 49: LEFT SIDE BRACKET INSTALLATIONS [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .......................... 2 0 0 FIGURE 50: RIGHT SIDE BRACKET INSTALLATIONS [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .................. 2 0 4 FIGURE 51: SEALANT AND PAINT APPLICATION [Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3] ................ 2 1 0 FIGURE 52: SEALANT AND PAINT APPLICATION [Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6] .......................... 2 1 2 FIGURE 53: GROUNDING FASTENER INSTALLATION [Group 1, 3-8, Configuration 2] ....... 2 1 4 FIGURE 54: GROUND BRACKET INSTALLATION [Group 1, Configuration 1-3; Group 3, Configuration 1-3;

Group 4, Configuration 1-3; Group 5, Configuration 1-3; Group 6, Configuration 1-3, 5-6; Group 7, Configuration 1-3, 5-6; Group 8, Configuration 1-3, 5-6] ................. 2 1 8 FIGURE 56: APPLICATION OF SEALANT ON FASTENERS COMMON TO STIFFENERS [Group 1, Configuration 2] ........................................ 2 2 2 FIGURE 57: APPLICATION OF SEALANT ON FASTENERS COMMON TO STIFFENERS [Group 3, Configuration 2] ........................................ 2 2 4 FIGURE 58: APPLICATION OF SEALANT ON FASTENERS COMMON TO STIFFENERS [Group 4-5, Configuration 2] ........................................ 2 2 6 FIGURE 59: APPLICATION OF SEALANT TO FASTENERS ON STIFFENERS [Group 6-8, Configuration 2] ................................................. 2 2 8 FIGURE 60: STIFFENER REMOVAL - LBL 6.15 [Group 6, Configuration 5-6; Group 7, Configuration 5-6;

Group 8, Configuration 5-6] .................................. 2 3 0 FIGURE 61: STIFFENER PRE-INSTALLATION - LBL 6.15 [Group 6, Configuration 5-6; Group 7, Configuration 5-6; Group 8, Configuration 5-6] ............................... 2 3 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.

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FIGURE 62: STIFFENER INSTALLATION - LBL 6.15 [Group 6, Configuration 5-6; Group 7, Configuration 5-6; Group 8, Configuration 5-6] ............................... 2 3 5 FIGURE 63: ANGLE INSTALLATION [Group 6, Configuration 5-6; Group 7, Configuration 5-6; Group 8, Configuration 5-6] ....................................... 2 3 8 APPENDIX A: PART DEMAND INTENT ................................... 2 4 1 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: 737-57A1269Original Issue: December 04, 2003 Revision 2: October 11, 2018 ATA System: 5712 SUBJECT: WINGS - Wing Center Section Rear Spar - Replacement of Stiffeners at Left and Right BBL 6.15 This revision includes all pages of the service bulletin.

COMPLIANCE INFORMATION RELATED TO THIS REVISION Federal Aviation Administration (FAA) Airworthiness Directive AD 2005-20-01 is related to this service bulletin.

The effective date of AD 2005-20-01 is November 01, 2005.

Federal Aviation Administration (FAA) Airworthiness Directive AD 2018-10-12 is related to this service bulletin.

The effective date of AD 2018-10-12 is June 07, 2018.

The Federal Aviation Administration (FAA) will possibly release an 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 the Original Issue or Revision 1 was previously done:

See Paragraph 1.D., Description for more information.

Airplanes with line numbers 1-291 were moved from Groups 1, 3, 4, and 5 and moved into Group 2. Group 2 now contains all 737-100/200/200C airplanes with line numbers 1-291. These airplanes are beyond the Limit of Validity (LOV).

REASON FOR REVISION This revision is sent to remove the stiffener inspection requirement, which is given in Boeing Service Bulletin 737-57A1339. In addition, this revision is sent to give compliance time for the stiffener replacement, to give instructions to install different fasteners for the stiffener replacement, and to add new bonding jumpers to restore fault current bonding path.

The data given in Information Notices 737-57A1269 IN 01, IN 02, IN 03 and IN 04 are included in this revision.

Terminology defined in Paragraph 3.A., General Information - Notes, only applies to the Accomplishment Instructions added in Revision 2 of this Service Bulletin.

These sections were changed:

1. In Subject, changed the description due to removal of the inspection requirement.

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2. In Summary, Concurrent Requirements, added a sentence referring to Paragraph 1.B., Concurrent Requirements.

3. In Summary, Background, updated new background information and added references to related documents.

4. In Summary, Action, updated to give stiffener replacement information with applicable group-configuration.

5. In Summary, Effectivity, added a sentence referring to Paragraph 1.A.1., Airplanes.

6. In Summary, Compliance, updated to give information related to Airworthiness Directives.

7. In Summary Manpower, changed information to include a reference to Paragraph 1.G., Manpower.

8. In Summary, Material Information, added information to include reference to APPENDIX A, Operator Supplied Parts/Materials and Paragraph 2.A., Material - Price and Availability.

9. In Summary Illustration, changed summary text.

10. In Paragraph 1.A.1, Effectivity, created new configurations for Groups 1, 3-8 for airplanes that have done previous replacements of stiffeners, added nitrogen generation systems, or done other repairs.

Changed Group 2 to cover airplanes beyond Limit of Validity.

11. In Paragraph 1.B., Concurrent Requirements, added a new requirement.

12. In Paragraph 1.C., Reason, updated new background information, added references to related documents, and added reason for this revision.

13. In Paragraph 1.D., Description, updated to give stiffener replacement information with applicable group-configuration due to changes in the compliance information, added effects of this revision information, and added Affected Maintenance Zones tables

14. In Paragraph 1.E., Compliance, updated to give information related to Airworthiness Directives. Added new compliance information related to stiffener replacement and restoring fault current bonding path with applicable group-configuration information.

15. In Paragraph 1.F., Approval, added paragraphs for Alternate Method of Compliance approval, statement of applicability to EASA/JAA Aircraft and statement for AWL.

16. In Paragraph 1.G., Manpower, updated and added manpower tables to reflect new and changed configurations.

17. In Paragraph 1.H., Weight and Balance Changes, updated the table.

18. In Paragraph 1.J.1., Existing Data, updated the reference list.

19. In Paragraph 1.K., Publications Affected, added information for Damage Tolerance Inspections.

20. In Paragraph 1.L., Interchangeability and Intermixability of Parts: Updated statement.

21. In Paragraph 2.A., Material - Price and Availability, changed tables to reflect new kits.

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22. In Paragraph 2.C.1., Kits/Parts, changed parts tables to reflect new kits and added statements to clarify kits.

23. In Paragraph 2.C.2., Parts and Materials Supplied by the Operator, updated the parts list.

24. In Paragraph 3.A., General Information, added notes.

25. In Paragraph 3.B., Work Instructions,

a. Added information for airplanes beyond the Limit of Validity and airplanes that do not require further action.

b. Updated group-configuration information throughout the work instructions.

c. Renumbered affected PART due to installation of the bonding jumper instructions.

d. PART I - deleted information.

e. PART II - added step to remove the time limited repair.

f. PART III - added a caution note and step to remove the time limited repair.

g. PART IV and PART V - removed references to Group 2 airplanes.

h. PART VI and PART VII - changed the PART description and moved the angle installation to PART VIII.

i. Added PART VIII to give installation of angle and bonding jumpers.

j. PART IX - updated close access information with applicable group-configuration information.

k. Added PART XI through PART XIII to give instructions for more work on airplane that have replaced the stiffeners.

26. Figure 1 - deleted information.

27. In Figures 2, 3, and 6, updated illustration.

28. In Figures 7, 8, 9, 10, 11, 26, 27, 28, 29, 30, 31, updated footnote (a).

29. In Figure 12, updated a part number.

30. In Figures 13, 14, 15, 32 and 33, added a note reflecting that bonding stud placement being reference only.

31. In Figures 16, 17, 18, 19, 34, 35, 36, 37 and 38, added fastener codes for grounding fasteners, updated hole diameters due to updated A-code fasteners and updated illustrations.

32. In Figures 20, 22, 23, 24, 39, 41, 42, 43 and 44, added fastener codes for grounding fasteners, updated A-code fasteners, and added instructions to apply sealant to fasteners inside the fuel tank.

33. Removed Figures 21 and 40 related to Group 2 airplanes.

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34. In Figures 25 and 45, updated fasteners.

35. In Figures 46, 47, and 48, updated illustrations and fastener information.

36. In Figures 49 and 50, updated fastener information.

37. In Figure 51, updated application of sealant step.

38. In Figures 52, updated illustration and application of sealant step.

39. Added Figures 53 to give instructions for grounding fasteners installation on airplanes which have replaced stiffeners.

40. Added Figure 54 to provide instructions for installing a ground bracket.

41. Added Figure 55 to provide instructions for installing bonding jumpers.

42. Added Figures 56, 57, 58, and 59, to give instructions to apply sealant to fasteners inside the fuel tank on airplanes which have replaced stiffeners.

43. Added Figures 60, 61, and 62, to give instructions for stiffener replacement to address a different configuration.

44. Added Figure 63, to give instructions for angle installation to address a different configuration.

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 December 04, 2003Original Issue:

September 16, 2004Revision 1:

October 11, 2018Revision 2:

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Commercial Airplanes 737 Service Bulletin ALERT SummaryNumber: 737-57A1269Original Issue: December 04, 2003 Revision 2: October 11, 2018 ATA System: 5712 SUBJECT: WINGS - Wing Center Section Rear Spar - Replacement of Stiffeners at Left and Right BBL 6.15

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 Refer to Paragraph 1.B., Concurrent Requirements.

BACKGROUND This service bulletin gives the instructions to replace the stiffeners at Left Buttock Line (LBL) 6.15 and Right Buttock Line (RBL) 6.15 on the rear spar of the wing center section.

Boeing has reports of cracks in the stiffeners at LBL 6.15 and RBL 6.15 on the wing center section rear spar.

One of the reports show that a crack was fully through the stiffener at RBL 6.15, just below the lower spar chord on a 737-200 airplane. Other reports show that cracks were found in these stiffeners on seven 737-300 airplanes.

On two of the 737-300 airplanes the cracks were fully through the stiffeners at LBL and RBL 6.15, and damage was also found on the keel beam structure.

The 737-200 airplane had 39,383 flight hours and 40,888 flight cycles. The 737-300 airplanes had 39,821 to 52,139 flight hours, and 20,697 to 47,496 flight cycles.

Continued operation with cracks in the stiffeners could cause damage to the keel beam structure. Damage, sufficient to reduce the load capability of the keel beam structure, could be one result.

The new improved stiffeners are made from 2024-T351 aluminum alloy plate and replace the stiffeners made from 7075-T6511 aluminum extrusion. The new stiffeners have increased flange thickness and also have two flanges for attachment to the center section rear spar, as compared to the existing stiffeners that have one flange for attachment to the spar. The new stiffener configuration gives the strength necessary to prevent cracks at LBL and RBL 6.15 on the wing center section rear spar.

After the release of Revision 1 of this service bulletin, Boeing has found that the replacement stiffener installation had degraded fault current bonding because it replaced the existing rivets (which provide an inherent bond path for fault currents and ground returns) with non-conductive finish K-code fasteners in transition fit holes. The replacement fasteners are not adequate in maintaining required fault current bonding path and thus, do not satisfy Special Federal Aviation Regulation (SFAR) 88 requirements. This revision is sent to update the instructions Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details.

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for airplanes that have not previously replaced their stiffeners and also to provide instructions for restoring the fault current bonding on airplanes that have previously replaced the stiffeners. The fault current bonding will be restored through strategic replacement of K-coded fasteners with A-coded (cadmium plated steel) fasteners in interference fit holes. In addition, four electrical bonding jumpers will be installed to maintain adequate fault current bonding between the hydraulic pumps and the web structure.

In addition to the above described electrical bonding issues, Boeing has received a report of cracks in the left side and right side keel beam upper chords when replacing the aft vertical stiffeners. Boeing has determined that the actual stresses on aft vertical stiffeners at LBL and RBL 6.15 are more than those used to design the structure and can cause fatigue cracks in the stiffeners. If the aft vertical stiffeners have cracks or are severed, the fatigue damage may extend into the adjacent keel beam structure and could reduce the limit load capability of the keel beam structure. Boeing has determined the inspections given in the Original Issue and Revision 1 of this service bulletin do not provide sufficient inspection intervals for timely crack detection in the aft vertical stiffeners. As a result, Boeing has issued Service Bulletin 737-57A1339 to inspect the stiffeners and keel beam upper chord structures.

Accomplishment of the Stiffener Replacements at LBL 6.15 and RBL 6.15 given in this service bulletin terminates the inspection requirements in accordance with Boeing Service Bulletin 737-57A1339.

Airworthiness Limitation (AWL) 28-AWL-11 listed in the Certification Maintenance Requirements (CMRs) document, D6-38278-CMR, is related to this service bulletin.

Boeing Structural Item Interim Advisory (SIIA) 737-273 is related to this service bulletin.

Boeing Service Related Problems (SRP) 737-SRP-57-0135, 737-SRP-57-0293, and 737-SRP-57-0343 are related to this service bulletin.

ACTION (PRR 35005-239RS) Group 2:

The Boeing Company endorses the FAA rules related to Limit of Validity (LOV) and recommends immediate and permanent removal from service of any airplanes upon reaching the LOV, whether or not it is operated under FAA jurisdiction. As such, The Boeing Company no longer provides maintenance instructions for airplanes that have accumulated flight cycles beyond the LOV. Airplanes in Group 2 (line number 1-291) have accumulated flight cycles beyond the LOV of the maintenance program. 14 CFR 121.1115 and 129.115 prohibit operation of an airplane beyond its LOV.

Group 1, 3-8, Configuration 4:

No further action required.

Group 1, Configuration 1, 3; Group 3, Configuration 1, 3; Group 4, Configuration 1, 3; Group 5, Configuration 1, 3; Group 6, Configuration 1, 3, 5-6; Group 7, Configuration 1, 3, 5-6; Group 8, Configuration 1, 3, 5-6:

Get access. Replace the stiffeners at LBL 6.15 and RBL 6.15 on the wing center section rear spar with the new improved stiffeners and do the installation of angle and bonding jumpers and close access.

Group 1, 3-8, Configuration 2:

Get access and do the installation of bonding fasteners and bonding jumpers, and sealing of fasteners and close access.

Original Issue: December 04, 2003 737-57A1269Revision 2: October 11, 2018 12 of 241 BOEING SERVICE BULLETIN 737-57A1269

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