# Boeing Alert Service Bulletin 737-53A1346: No revision named - Rights: © The Boeing Company. Filed by the FAA in regulations.gov docket FAA-2020-0689; AD 2020-26-04 incorporates this document by reference. Not covered by OpenAirDocs’ CC0 dedication. - Document: [Boeing Alert Service Bulletin 737-53A1346](https://openairdocs.org/service-documents/boeing/737-53a1346.md) - Title as filed: SB-737-53A1346-00 - Pages: 801 - PDF: https://openairdocs.org/files/sha256/eb/58/eb58e2410e57cdd9e2941c1fdd641bf91e66e714ae7f7ed442c0e7def111a474 - Page: https://openairdocs.org/service-documents/boeing/737-53a1346/file/eb58e2410e57 ## 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: 737-53A1346 Original Issue: March 27, 2020 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Fuselage Skin Chem-Mill Step Crack Inspection and Repair 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 © 2020 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 Unpublished Work.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: March 27, 2020 737-53A1346 1 of 801 5.0 ### Page 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 2 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT BLANK PAGE ### Page 3 Table of Contents Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1. PLANNING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 A. Effectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1. Airplanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2. Spares Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 B. Concurrent Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 C. Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 D. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 E. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 F. Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 G. Manpower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 H. Weight and Balance Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 I. Electrical Load Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 J. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 1. Existing Data: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 2. Data Supplied with this Service Bulletin: . . . . . . . . . . . . . . . . . . . . . . . . . . 135 3. Installation Drawings Used in the Preparation of this Service Bulletin: . . . . . . . . . . 136 K. Publications Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 L. Interchangeability and Intermixability of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 M. Software Accomplishment Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 2. MATERIAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 A. Material - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 B. Industry Support Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 C. Parts Necessary for Each Airplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 1. Kits/Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 2. Parts and Materials Supplied by the Operator . . . . . . . . . . . . . . . . . . . . . . . 139 3. Parts Modified and Reidentified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 4. Parts Removed and Not Replaced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 D. Parts Necessary to Change Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 E. Special Tooling - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 F. Special Tooling Necessary to do this Service Bulletin . . . . . . . . . . . . . . . . . . . . . . 143 3. ACCOMPLISHMENT INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 A. GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 B. WORK INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 FIGURE 1: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 1, 22] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 FIGURE 2: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 2, 13, 24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 FIGURE 3: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 23] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 FIGURE 4: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 3, 9-10, 14-15, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 FIGURE 5: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 4, 11, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 FIGURE 6: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 5, 12, 17] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 3 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 4 FIGURE 7: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 18, 21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 FIGURE 8: FUSELAGE - SKIN AND TEAR STRAP INSPECTIONS AT CHEM-MILL STEPS COMMON TO LAP JOINTS [Group 19-20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 FIGURE 9: FUSELAGE - WINDOW BELT INSPECTION FOR ANY HORIZONTAL CHEM-MILL STEP CRACK [Group 3, 9-10, 14-15, 18, 21, 25] . . . . . . . . . . . . . . . . . . . . . . . . . 306 FIGURE 10: FUSELAGE - WINDOW BELT INSPECTION FOR ANY HORIZONTAL CHEM-MILL STEP CRACK [Group 4, 11, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 FIGURE 11: FUSELAGE - WINDOW BELT INSPECTION FOR ANY HORIZONTAL CHEM-MILL STEP CRACK [Group 5, 12, 17, 19-20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 FIGURE 12: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 1, 22] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 FIGURE 13: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 2, 13, 24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 FIGURE 14: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 23] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 FIGURE 15: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 3, 5, 14, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 FIGURE 16: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 9-10, 12, 15, 17] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 FIGURE 17: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 4] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 FIGURE 18: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 11, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 FIGURE 19: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 19, 21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366 FIGURE 20: FUSELAGE - SKIN CHEM-MILLED POCKETS VERTICAL CRACK INSPECTION [Group 18, 20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 FIGURE 21: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANEL INSPECTION FOR ANY CRACK [Group 1, 22] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380 FIGURE 22: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANEL INSPECTION FOR ANY CRACK [Group 2, 13, 23-24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 FIGURE 23: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANEL INSPECTION FOR ANY CRACK [Group 3, 6, 9-10, 14-15, 18, 21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 FIGURE 24: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANEL INSPECTION FOR ANY CRACK [Group 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 FIGURE 25: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANEL INSPECTION FOR ANY CRACK [Group 4, 7, 11, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 FIGURE 26: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANEL INSPECTION FOR ANY CRACK [Group 5, 8, 12, 17, 19-20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 FIGURE 27: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION FOR ANY CRACK [Group 1, 22] . 428 FIGURE 28: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION FOR ANY CRACK [Group 2-3, 24-25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 FIGURE 29: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION FOR ANY CRACK [Group 23] . 442 FIGURE 30: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION FOR ANY CRACK [Group 4-5, 13-14, 19, 21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 FIGURE 31: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION FOR ANY CRACK [Group 9-12, 15-18, 20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456 FIGURE 32: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION FOR ANY CRACK [Group 6-8] . 460 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 4 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 5 FIGURE 33: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION AT KNOWN CRACK LOCATIONS [Group 1, 3-5, 13-14, 19, 21-25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 FIGURE 34: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION AT KNOWN CRACK LOCATIONS [Group 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 FIGURE 35: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION AT KNOWN CRACK LOCATIONS [Group 3, 14, 21, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 FIGURE 36: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION AT KNOWN CRACK LOCATIONS [Group 3, 9-10, 14-15, 18, 21, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 FIGURE 37: FUSELAGE - SECTION 41 SKIN PANEL INSPECTION AT KNOWN CRACK LOCATIONS [Group 5, 12, 17, 19-20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 FIGURE 38: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 1, 22] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 FIGURE 39: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 2, 13, 24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486 FIGURE 40: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 23] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495 FIGURE 41: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 3, 9-10, 14-15, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504 FIGURE 42: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 18, 21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514 FIGURE 43: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 4, 11, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523 FIGURE 44: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 5, 12, 17] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 FIGURE 45: FUSELAGE - SECTION 43 AND SECTION 46 CROWN SKIN INSPECTION FOR ANY CRACK [Group 19-20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 FIGURE 46: FUSELAGE - MODIFICATION CATEGORY C REPAIR TO A SRM REPAIR AT A LAP JOINT LOCATION - LAP JOINT INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 FIGURE 47: FUSELAGE - MODIFICATION CATEGORY C REPAIR TO A SERVICE BULLETIN REPAIR AT A NON LAP JOINT - BONDED DOUBLER INSPECTION . . . . . . . . . . . . . . . 555 FIGURE 48: FUSELAGE - CATEGORY C SKIN REPAIR AT A LAP JOINT - EXTERNAL INSPECTION. 559 FIGURE 49: FUSELAGE - CATEGORY C SKIN REPAIR AT A LAP JOINT - FASTENER REMOVAL AND SKIN TRIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562 FIGURE 50: FUSELAGE - CATEGORY C SKIN REPAIR AT A LAP JOINT - FABRICATION . . . . . 565 FIGURE 51: FUSELAGE - CATEGORY C REPAIR AT A LAP JOINT - INSTALLATION . . . . . . . . 569 FIGURE 52: FUSELAGE - CATEGORY C SKIN REPAIR AT A NON LAP JOINT - INSPECTION . . . 573 FIGURE 53: FUSELAGE - CATEGORY C SKIN REPAIR AT A NON LAP JOINT - FASTENER REMOVAL AND SKIN TRIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 FIGURE 54: FUSELAGE - CATEGORY C SKIN REPAIR AT A NON LAP JOINT - FABRICATION . . 578 FIGURE 55: FUSELAGE - CATEGORY C SKIN REPAIR AT A NON LAP JOINT - INSTALLATION . 581 FIGURE 56: FUSELAGE - PREVENTIVE MODIFICATION FOR WINDOW BELT HORIZONTAL CHEM-MILL STEP CRACK - INSPECTION AND FASTENER REMOVAL [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 FIGURE 57: FUSELAGE - PREVENTIVE MODIFICATION FOR WINDOW BELT HORIZONTAL CHEM-MILL STEP CRACK - FABRICATION [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . . . . . . . . . 588 FIGURE 58: FUSELAGE - PREVENTIVE MODIFICATION FOR WINDOW BELT HORIZONTAL CHEM-MILL STEP CRACK - INSTALLATION [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . . . . . . . . . 592 FIGURE 59: FUSELAGE - SKIN CHEM-MILL STEP CRACK AT STRINGER 12 REPAIR - INSPECTION AND FASTENER REMOVAL AND CUT-OUT [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . . 598 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 5 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 6 FIGURE 60: FUSELAGE - SKIN CHEM-MILL STEP CRACK AT STRINGER 12 REPAIR - FABRICATION [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 FIGURE 61: FUSELAGE - SKIN CHEM-MILL STEP CRACK AT STRINGER 12 REPAIR - INSTALLATION [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . 607 FIGURE 62: FUSELAGE - POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF THE STRINGER 12 REPAIR FOR ANY CRACK [Group 3, 5, 9-10, 12, 14-15, 17-21, 25] . 614 FIGURE 63: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 2, 23] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617 FIGURE 64: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 13, 24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624 FIGURE 65: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 FIGURE 66: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 22] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 640 FIGURE 67: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 3, 6, 9-10, 14-15, 18, 21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647 FIGURE 68: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 25] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655 FIGURE 69: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 4, 7, 11, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662 FIGURE 70: FUSELAGE - SECTION 43 LOWER LOBE SKIN PANELS WFD INSPECTION FOR ANY CRACK [Group 5, 8, 12, 17, 19-20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671 FIGURE 71: CATEGORY C/TIME-LIMITED REPAIR AT A NON LAP JOINT CONVERSION INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678 FIGURE 72: OPTION 1 TO MAKE CATEGORY C REPAIR A SERVICE BULLETIN REPAIR WITH A DOUBLER, SOLID FASTENERS AND TEAR STRAP DOUBLERS . . . . . . . . . . . . 680 FIGURE 73: OPTION 2 TO MAKE CATEGORY C REPAIR A SERVICE BULLETIN REPAIR WITH A LARGER DOUBLER, SOLID FASTENERS AND TEAR STRAP DOUBLERS . . . . . . . . . . . . 686 FIGURE 74: POST REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF SERVICE BULLETIN REPAIR, OPTION 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692 FIGURE 75: POST REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF SERVICE BULLETIN REPAIR, OPTION 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694 APPENDIX A: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK [Group 1-5, 9-25, Configuration 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696 APPENDIX B: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 2: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK [Group 1-5, 9-25, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 APPENDIX C: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 3: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK [Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708 APPENDIX D: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 4: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK [Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713 APPENDIX E: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 5: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK [Group 4, 11, 16, Configuration 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718 APPENDIX F: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 6: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK [Group 4, 11, 16, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 6 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 7 APPENDIX G: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 7: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK [Group 1-2, 13, 22-24, Configuration 1] . . . . . 724 APPENDIX H: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 8: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK [Group 1-2, 13, 22-24, Configuration 2] . . . . . 728 APPENDIX I: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 9: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK [Group 3-5, 9-12, 14-21, 25, Configuration 1] . 732 APPENDIX J: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 10: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK [Group 3-5, 9-12, 14-21, 25, Configuration 2] . 738 APPENDIX K: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 11: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 LOWER LOBE FOR ANY CRACK [Group 1-25, Configuration 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744 APPENDIX L: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 12: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 LOWER LOBE FOR ANY CRACK [Group 1-25, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 748 APPENDIX M: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 13: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 41 FOR ANY CRACK [Group 1-25, Configuration 1] . 752 APPENDIX N: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 14: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 41 FOR ANY CRACK [Group 1-25, Configuration 2] . 757 APPENDIX O: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 15: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 AND SECTION 46 CROWN SKIN FOR ANY CRACK [Group 1-2, 13, 22-24, Configuration 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . 762 APPENDIX P: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 16: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 AND SECTION 46 CROWN SKIN FOR ANY CRACK [Group 1-2, 13, 22-24, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . 766 APPENDIX Q: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 17: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 AND SECTION 46 CROWN SKIN FOR ANY CRACK [Group 3-5, 9-12, 14-21, 25, Configuration 1] . . . . . . . . . . . . . . . . . . . . . . . . 771 APPENDIX R: LOGIC DIAGRAM FOR PARAGRAPH 1.E., TABLE 18: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 AND SECTION 46 CROWN SKIN FOR ANY CRACK [Group 3-5, 9-12, 14-21, 25, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . 777 APPENDIX S: LOGIC DIAGRAM FOR PARAGRAPH 1.E., COMPLIANCE TABLE 19: POST-REPAIR DETAILED INSPECTION OF CATEGORY C REPAIR INSTALLED IN ACCORDANCE WITH THIS SERVICE BULLETIN FOR ANY CRACK AND FOR ANY LOOSE, MISSING, OR DAMAGED FASTENERS [Group 1-25, Configuration 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783 APPENDIX T: LOGIC DIAGRAM FOR PARAGRAPH 1.E., COMPLIANCE TABLE 20: POST-REPAIR DETAILED INSPECTION OF TIME-LIMITED REPAIR INSTALLED IN ACCORDANCE WITH SERVICE BULLETIN 737-53A1210 REVISION 3 FOR ANY CRACK [Group 1-25, Configuration 1] . 788 APPENDIX U: LOGIC DIAGRAM FOR PARAGRAPH 1.E., COMPLIANCE TABLE 21: POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF THE STRINGER 12 CHEM-MILL CRACK REPAIR FOR ANY CRACK [Group 3-5, 9-12, 14-21, 25, Configuration 1] . . . 793 APPENDIX V: LOGIC DIAGRAM FOR PARAGRAPH 1.E., COMPLIANCE TABLE 22: WIDESPREAD FATIGUE DAMAGE (WFD) DETAILED AND NON-DESTRUCTIVE TEST (NDT) INSPECTIONS OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 LOWER LOBE S-19 TO S-26 FOR ANY CRACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 APPENDIX W: LOGIC DIAGRAM FOR PARAGRAPH 1.E., COMPLIANCE TABLE 23: POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF SERVICE BULLETIN REPAIRS INSTALLED IN ACCORDANCE WITH PART 16: MODIFICATION CATEGORY C REPAIR TO SERVICE BULLETIN REPAIR AT THE NON LAP JOINT LOCATION . . . . . . . . . . . 800 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 7 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 8 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 8 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT BLANK PAGE ### Page 9 Commercial Airplanes 737 Service Bulletin ALERT SummaryNumber: 737-53A1346Original Issue: March 27, 2020 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Fuselage Skin Chem-Mill Step Crack Inspection and Repair 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 and repair for cracking along the chem-mill steps on the fuselage skin from STA 259.5 to STA 1016. This service bulletin will supersede Service Bulletin (SB) 737-53A1210 Revision 3 and will contain all requirements of SB 737-53A1210 Revision 3 with the exception of lower lobe chem-mill cracking between STA 727 and STA 1016. The lower lobe chem-mill cracking between STA 727 and STA 1016 is the subject of Service Bulletins 737-53-1065 (737-200/-200C), 737-53-1168 (737-300), 737-53-1187 (737-400) and 737-53-1315 (737-500). In addition, this service bulletin was created to expand the Non-Destructive Test (NDT) inspection areas of the skin to all horizontal and vertical chem-mill step locations with a history of cracking between STA 259.5 to STA 1016 and to include the requirements to prevent Widespread Fatigue Damage (WFD) in the fuselage skin due to cracking in the chem-mill steps. Accomplishment of this service bulletin will allow early detection of cracks at the step of the chem-mill pockets and prevent WFD by reducing the chance of multiple adjacent chem-mill step cracks for linking with each other. Continued operation of the airplane with undetected chem-mill steps cracks could result in an uncontrolled decompression of the airplane and loss of structural integrity of the airplane. Boeing has received a large number of reports of horizontal and vertical chem-mill step cracks while accomplishing the inspections in accordance with Service Bulletin 737-53A1210. The service history table below provides further descriptions of operator findings. Cracks found at the step of the chem-mill pockets are caused by fatigue from hoop stress and higher than expected bending stresses across the chem-mill steps. Multiple site damage leading to simultaneous chem-mill step cracking in consecutive bays is the source for WFD. The fuselage skin panels with side-by-side chem-mill pockets have been identified to be structure that is susceptible to WFD. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 9 of 801 ### Page 10 Service History ReportTotal Flight Cycles Operators have reported horizontal cracks along the edges of the chem-milled pockets in the skin at S-12 in the bay forward of STA 520 and just above the S-4, S-10, and S-14 lap joints. Horizontal chem-mill line cracks have also been found in non-lap joint areas of the fuselage crown skin and at the tear strap attachments to the fuselage skin. The chem-mill line crack were up to 8 inches long, and multiple adjacent bays have been found cracked along the same stringer. 23,425 - 64,420 Operators have reported horizontal skin cracks along the edges of the chem-milled pockets in the skin below S-14 in Section 41. The cracks were up to 7.25 inches long. 22,786 - 80,113 Operators have reported circumferential cracks along the vertical chem-mill steps of the fuselage skin next to the STA 360, STA 727, and STA 908 butt joints from S-3R to S-7R. Cracks have been found in multiple adjacent bays and have varied in length from 0.75 inch to 4 inches. 45,100 - 67,400 Boeing Service Related Problems (SRP) 737-SRP-53-0503 and 737-SRP-53-0394 are related to this service bulletin. Boeing Fleet Team Digest (FTD) 737 FTD 53-14004 is 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 Parts/Material Paragraph 2.F., Special Tooling Necessary to do this Service Bulletin NoSpecial Tooling Required Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 10 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 11 ACTION Group 1-5, 9-25: 1. Do the following inspections of the fuselage skin for any crack: a. Do an external detailed and NDT inspection of the fuselage skin from S-10L to S-10R for any vertical crack along the chem-mill step lines just forward and aft of STA 360, STA 540, STA 727, and STA 908 for 737-200/200C/300/500 airplanes and STA 360, STA 500C, BS 540, STA 727, STA 727G and STA 908 for 737-400 airplanes and at known locations. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. b. Do an external detailed or external detailed and NDT inspection for any crack in the fuselage skin from STA 259.5 to STA 360 along the horizontal chem-mill step line. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. c. Do an external detailed or external detailed and NDT inspection for any crack in the fuselage skin from STA 360 to STA 1016 and S-10L to S-10R along the horizontal chem-mill step line. Skin inspection figures given in this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. d. Do an external detailed or external detailed and NDT inspection of the Section 43 lower lobe skin for any crack from S-14 to S-26 left and right from STA 360 to STA 540 along the horizontal chem-mill step line. Skin inspection figures given in this service bulletin show specific areas to inspect for any crack along the chem-mill step line at Section 43 lower lobe. e. Do an external detailed and NDT inspection of the window belt dummy bay locations along the horizontal chem-mill step lines of the fuselage skin from S-10 to S-14 left and right and STA 500D to STA 520 for 737-300 airplanes, STA 500E to STA 500F and STA 500G to STA 520 for 737-400 airplanes and STA 482B to STA 520 for 737-500 airplanes for any crack. f. Do an external detailed and NDT inspection for any horizontal crack along the chem-mill step lines of the fuselage skin from STA 360 to STA 1016 at the lap joints S-4, S-10 and S-14 left and right. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. g. Do an external High Frequency Eddy Current (HFEC) inspection for any crack in the fuselage skin at the tear strap attachments from STA 360 to STA 1016 at the lap joints S-4, S-10 and S-14 left and right. 2. If any crack is found, do the repair in accordance with this service bulletin or contact The Boeing Company for repair instructions and do the repair. 3. If no crack is found, repeat the detailed and NDT inspections at the intervals given in Paragraph 1.E., Compliance. Group 6-8: 1. Do the following inspections of the fuselage skin for any crack: Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 11 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 12 a. Do an external detailed inspection for any crack in the fuselage skin from STA 259.5 to STA 360 along the horizontal chem-mill step line. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. b. Do an external detailed or external detailed and NDT inspection of the Section 43 lower lobe skin for any crack from S-14 to S-26 left and right from STA 360 to STA 540 along the horizontal chem-mill step line. Skin inspection figures given in this service bulletin show specific areas to inspect for any crack along the chem-mill step line at Section 43 lower lobe. 2. If any crack is found, do the repair in accordance with this service bulletin or contact The Boeing Company for repair instructions and do the repair. 3. If no crack is found, repeat the detailed and NDT inspections at the intervals given in Paragraph 1.E., Compliance. Group 26: 1. The Boeing Company endorses the new 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 26 (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. EFFECTIVITY 737-100/-200/-200C/-300/-400/-500 Airplanes. Refer to Paragraph 1.A.1., Airplanes, for the list of affected airplanes. COMPLIANCE Federal Aviation Administration (FAA) Airworthiness Directives AD 2009-07-11, AD 2017-20-12, AD 2017-20-14 and AD 2013-18-08 are related to this service bulletin. 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. Refer to Paragraph 1.E., Compliance. INDUSTRY SUPPORT INFORMATION Boeing warranty remedies are not available for the inspection and repair procedures given in this service bulletin. MANPOWER Refer to Paragraph 1.G., Manpower. MATERIAL INFORMATION Operator Supplied Parts/Materials. Refer to Paragraph 2.A., Material - Price and Availability. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 12 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 13 (OCR) BOEING SERVICE BULLETIN 737-53A1346 ALERT ALERT DO AN EXTERNAL DETAILED AND NDT INSPECTION OF VERTICAL CRACK ALONG THE CHEM-MILL STEP LINES. THE FUSELAGE SKIN FROM S-10L TO S-10R FOR ANY STA 1016 STA 908 DO AN EXTERNAL DETAILED OR EXTERNAL DETAILED AND NDT STA INSPECTION FOR 727G ANY CRACK IN THE FUSELAGE SKIN STA FROM STA 259.5 TO 540 STA 360 ALONG THE STA HORIZONTAL 727 CHEM-MILL STEP LINE STA 000000 360 STA STA PR 259.5 500C • DO AN EXTERNAL DETAILED AND NDT INSPECTIONS FOR ANY HORIZONTAL CRACK ALONG THE CHEM-MILL STEP LINES OF THE FUSELAGE SKIN FROM STA 360 TO STA 1016 AT LAP JOINTS S-4, S-10 0000000000-0 AND S-14 LEFT AND RIGHT. DO AN EXTERNAL HIGH FREQUENCY S-4L EDDY CURRENT (HFEC) INSPECTION FOR ANY CRACK IN THE FUSELAGE SKIN AT THE TEAR STRAP ATTACHMENTS FROM S-10L* STA 360 TO STA 1016 AT THE LAP JOINTS S-14L S-15L S-4, S-10 AND S-14 LEFT AND RIGHT. DO AN EXTERNAL DETAILED OR EXTERNAL DETAILED AND NDT INSPECTION FOR ANY CRACK IN THE FUSELAGE SKIN FROM STA 360 TO STA 1016 AND S-10L TO S-10R ALONG THE HORIZONTAL CHEM-MILL STEP LINE. DO AN EXTERNAL DETAILED AND NDT INSPECTION OF THE WINDOW BELT DUMMY BAY LOCATIONS ALONG THE HORIZONTAL CHEM-MILL STEP LINES OF THE FUSELAGE SKIN FROM S-10 TO S-14 LEFT AND RIGHT DO AN EXTERNAL DETAILED OR EXTERNAL DETAILED AND NDT INSPECTION OF THE SECTION 43 LOWER LOBE SKIN FOR ANY CRACK FROM S-14 TO S-26 LEFT AND RIGHT FROM STA 360 TO STA 540 ALONG THE HORIZONTAL CHEM-MILL STEP LINE. SKIN INSPECTION FIGURES GIVEN IN THIS SERVICE BULLETIN SHOW SPECIFIC AREAS TO INSPECT FOR ANY CRACK ALONG THE CHEM-MILL STEP LINE OF THE FUSELAGE SKIN. F ANY CRACK IS FOUND IN ANY OF THE ABOVE INSPECTIONS, REPAIR THE SKIN DAMAGE IN ACCORDANCE WITH THIS SERVICE BULLETIN OR CONTACT THE BOEING COMPANY FOR REPAIR INSTRUCTIONS AND DO THE REPAIR. LEFT SIDE SHOWN, RIGHT SIDE SIMILAR 737-400 SHOWN, 2295783 OTHER MODELS ARE SIMILAR Original Issue: March 27, 2020 Export Controlled ECCN: 9E991 - BOEING 737-53A1346 PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. 13 of 801 ### Page 14 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 14 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT BLANK PAGE ### Page 15 Commercial Airplanes 737 Service Bulletin ALERT Number: 737-53A1346 Original Issue: March 27, 2020 ATA System: 5331 SUBJECT: FUSELAGE - Skin - Fuselage Skin Chem-Mill Step Crack Inspection and Repair 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 737-100, 737-200, 737-200C, 737-300, 737-400, 737-500 Airplane(s), line number(s) 1-2565 in 26 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 D6-19567 Part 3 for Airplane Variable Number, Line Number, and Serial Number data. DESCRIPTIONCONFIGURATIONGROUP 737-200C Airplanes that have a different Section 43 lower lobe skin configuration to Group 22. - 1 737-200C Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-200C Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 15 of 801 ### Page 16 DESCRIPTIONCONFIGURATIONGROUP 737-200 Airplanes that have a different Section 41 skin configuration to Group 13 and 23, a different Section 43 lower lobe skin configuration to Groups 13 and 24 and a different Crown skin configuration to Group 23. - 2 737-200 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-200 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-300 Airplanes that have a different Section 41 skin configuration to Groups 6, 9, 10, 14, 15, 18 and 21, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 6, 18 and 21. - 3 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-400 Airplanes that have a different Section 41 skin configuration to Groups 7, 11 and 16, and a different Crown skin configuration to Group 7. - 4 737-400 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-400 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-500 Airplanes that have a different Section 41 skin configuration to Groups 8, 12, 17 and 20, and a different Crown skin configuration to Groups 8, 19 and 20. - 5 737-500 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-500 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 16 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 17 DESCRIPTIONCONFIGURATIONGROUP 737-300 Airplanes that have a different Section 41 and crown skin configuration to Groups 3, 9, 10, 14, 15, 18, 21 and 25 and a different Section 43 lower lobe skin configuration to Group 25. - 6 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-400 Airplanes that have a different Section 41 and crown skin configuration to Groups 4, 11 and 16. - 7 737-400 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-400 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-500 Airplane that have a different Section 41 and crown skin configuration to Groups 5, 12, 17, 19 and 20. - 8 737-500 Airplane that have accomplished Service Bulletin 737-53A1210. 1 737-500 Airplane that have not accomplished Service Bulletin 737-53A1210. 2 737-300 Airplanes that have a different Section 41 skin configuration to Groups 3, 6, 14, 21 and 25, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 6, 18 and 21, and a different Section 46 skin configuration to Groups 10 and 15 between STA 727 and STA 907 at S-14. - 9 737-300 Airplane that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplane that have not accomplished Service Bulletin 737-53A1210. 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 17 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 18 DESCRIPTIONCONFIGURATIONGROUP 737-300 Airplanes that have a different Section 41 skin configuration to Groups 3, 6, 14, 21 and 25, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 6, 18 and 21, and a different Section 46 skin configuration to Groups 9 and 15 between STA 727 and STA 907 at S-14. - 10 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-400 Airplanes that have a different Section 41 skin configuration to Groups 4 and 7, a different crown skin configuration to Group 7, and a different Section 46 skin configuration to Group 16 between STA 727 and STA 907 at S-14. - 11 737-400 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-400 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-500 Airplanes that have a different Section 41 skin configuration to Groups 5, 8 and 19, and a different Crown skin configuration to Group 8, 19 and 20, and a different Section 46 skin configuration to Group 17 between STA 727 and STA 907 at S-14. - 12 737-500 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-500 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-200 Airplanes that have a different Section 41 skin configuration to Groups 2, 23 and 24, a different Section 43 lower lobe skin configuration to Groups 2 and 23 and a different Crown skin configuration to Group 23. - 13 737-200 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-200 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 18 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 19 DESCRIPTIONCONFIGURATIONGROUP 737-300 Airplanes that have a different Section 41 skin configuration to Groups 3, 6, 9, 10, 15, 18 and 25, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 6, 18 and 21. - 14 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-300 Airplanes that have a different Section 41 skin configuration to Groups 3, 6, 14, 21 and 25, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 6, 18 and 21, and a different Section 46 skin configuration to Groups 9 and 10 between STA 727 and STA 907 at S-14. - 15 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-400 Airplanes that have a different Section 41 skin configuration to Groups 4 and 7, and a different Crown skin configuration to Group 7, and a different Section 46 skin configuration to Group 11 between STA 727 and STA 907 at S-14. - 16 737-400 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-400 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-500 Airplanes that have a different Section 41 skin configuration to Groups 5, 8 and 19, and a different Crown skin configuration to Group 8, 19 and 20, and a different Section 46 skin configuration to Group 12 between STA 727 and STA 907 at S-14. - 17 737-500 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-500 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 19 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 20 DESCRIPTIONCONFIGURATIONGROUP 737-300 Airplanes that have a different Section 41 skin configuration to Groups 3, 6, 14, 21 and 25, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 3, 6, 9, 10, 14, 15 and 25. - 18 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-500 Airplanes that have a different Section 41 skin configuration to Groups 8, 12, 17 and 20, and a different Crown skin configuration to Group 5, 8, 12 and 17. - 19 737-500 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-500 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-500 Airplanes that have a different Section 41 skin configuration to Groups 5, 8, and 19, and a different Crown skin configuration to Group 5, 8, 12 and 17. - 20 737-500 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-500 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-300 Airplanes that have a different Section 41 skin configuration to Groups 3, 6, 9, 10, 15, 18 and 25, a different Section 43 lower lobe skin configuration to Group 25 and a different Crown skin configuration to Groups 3, 6, 9, 10, 14, 15 and 25. - 21 737-300 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 20 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 21 DESCRIPTIONCONFIGURATIONGROUP 737-200C Airplanes that have a different Section 43 lower lobe skin configuration to Group 1. - 22 737-200C Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-200C Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-200 Airplanes that have a different Section 41 skin configuration to Group 2,13 and 24, a different Section 43 lower lobe skin configuration to Groups 13 and 24, and a different Crown skin configuration to Groups 2, 13 and 24. - 23 737-200 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-200 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-200 Airplanes that have a different Section 41 skin configuration to Group 13 and 23, a different Section 43 lower lobe skin configuration to Groups 2 and 23, and a different Crown skin configuration to Group 23. - 24 737-200 Airplanes that have accomplished Service Bulletin 737-53A1210. 1 737-200 Airplanes that have not accomplished Service Bulletin 737-53A1210. 2 737-300 Airplane that have a different Section 41 skin configuration to Groups 6, 9, 10, 14, 15, 18 and 21, a different Section 43 lower lobe skin configuration to Groups 3, 6, 9, 10, 14, 15, 18 and 21, and a different Crown skin configuration to Groups 6, 18 and 21. - 25 737-300 Airplane that have accomplished Service Bulletin 737-53A1210. 1 737-300 Airplane that have not accomplished Service Bulletin 737-53A1210. 2 737-100/-200/-200C Airplanes, line numbers 1 to 291.- 26 Airplane Models: 737-100, 737-200, 737-200C, 737-300, 737-400, 737-500 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 21 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 22 GroupVariable Number 26PA001 - PA022 26PA099 26PA231 - PA232 26PC001 - PC005 26PG001 - PG075 26PG199 26PG201 - PG230 26PG251 - PG255 26PG271 - PG279 26PG301 - PG314 26PG331 - PG332 26PG351 - PG356 26PG375 26PG401 - PG403 26PG431 - PG442 26PG471 - PG475 26PG501 - PG505 26PG571 - PG583 2PG584 - PG586 26PG621 - PG630 26PG651 - PG652 26PG701 - PG705 2PH001 2PH011 - PH013 2PH021 - PH024 26PH701 - PH715 26PH731 - PH732 26PH741 - PH742 2PH743 26PJ001 - PJ002 2PJ003 - PJ009 26PJ031 - PJ032 26PJ071 - PJ072 GroupVariable Number 26PJ101 - PJ104 2PJ105 - PJ119 23PJ201 - PJ219 16PJ301 - PJ302 11PJ551 7PJ552 2PK026 - PK029 2PK041 - PK053 2PK061 - PK070 2PK081 - PK082 2PK091 - PK099 2PK101 - PK103 2PK111 - PK120 2PK141 - PK146 2PK201 - PK204 2PK211 - PK215 24PK216 - PK220 2PK221 - PK223 2PK231 - PK241 2PK251 - PK258 2PK271 - PK274 2PK281 - PK289 2PK291 2PK301 - PK318 2PK341 2PK351 - PK361 2PK391 2PK431 - PK433 2PK451 - PK452 2PK461 - PK469 2PK495 2PK501 - PK504 2PK511 - PK514 GroupVariable Number 24PK515 2PK519 2PK521 - PK525 24PK526 - PK527 13PK528 2PK541 - PK564 24PK565 2PK581 2PK591 - PK599 2PK601 - PK617 2PK621 - PK637 2PK641 - PK642 2PK661 - PK664 24PK665 - PK666 2PK671 - PK680 24PK681 2PK691 - PK697 2PK711 - PK716 2PK731 - PK749 24PK750 - PK765 2PK771 - PK779 2PK801 - PK804 2PK819 - PK827 2PK830 2PK861 - PK863 2PK871 - PK874 2PK881 - PK884 2PK901 - PK932 24PK933 - PK938 2PK971 - PK974 2PL001 - PL028 2PL061 2PL081 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 22 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 23 GroupVariable Number 2PL101 - PL113 2PL151 2PL171 - PL172 2PL201 - PL203 2PL221 2PL401 - PL417 2PL421 2PL441 2PL451 - PL454 24PL455 - PL456 2PL471 2PL491 2PL501 - PL506 2PL551 - PL562 2PL581 2PL601 - PL603 2PL611 2PL621 - PL623 24PL624 - PL625 13PL626 2PL631 - PL632 26PL711 - PL712 26PL716 2PL717 - PL745 24PL746 13PL747 2PL756 2PL758 2PL761 - PL770 2PL781 - PL788 2PL793 26PL801 - PL803 2PM001 - PM006 GroupVariable Number 2PM016 - PM017 2PM021 - PM023 2PM051 - PM062 24PM063 - PM066 2PM101 - PM119 2PM141 - PM142 24PM171 24PM181 24PM251 - PM255 24PM281 - PM283 14PM381 - PM392 15PM393 - PM395 9PM396 - PM399 9PM401 - PM417 9PM541 10PM542 6PM543 - PM547 16PM551 - PM564 2PN001 - PN002 2PN021 - PN035 24PN036 - PN043 2PN081 - PN086 2PN101 - PN112 24PN113 - PN117 24PN131 - PN163 24PN401 - PN420 24PN431 - PN433 24PN451 - PN456 24PN471 - PN472 13PN473 - PN474 24PN481 24PN491 - PN492 13PN493 GroupVariable Number 24PN501 13PN502 13PN511 - PN512 13PN521 3PP001 - PP031 14PP032 - PP054 3PP101 - PP126 21PP127 - PP148 18PP149 - PP160 3PP161 - PP168 14PP169 3PP181 - PP184 14PP185 - PP199 3PP201 - PP204 14PP205 25PP221 3PP231 - PP243 3PP281 - PP286 3PP301 - PP305 3PP351 - PP352 14PP353 3PP376 - PP384 14PP391 - PP393 3PP401 - PP424 14PP425 - PP440 3PP471 - PP475 3PP501 - PP504 14PP505 - PP510 9PP511 - PP517 3PP521 - PP522 3PP631 - PP634 3PP651 - PP652 3PP671 - PP699 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 23 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 24 GroupVariable Number 3PP701 - PP720 14PP721 - PP733 3PP771 - PP777 14PP778 - PP779 3PP801 - PP804 14PP805 - PP808 3PP821 - PP827 3PP831 - PP836 14PP837 - PP845 3PP846 - PP848 3PP851 14PP852 3PP861 - PP870 14PP871 - PP873 9PP874 - PP875 3PP891 - PP899 3PP901 - PP905 14PP906 - PP924 15PP925 9PP926 - PP930 3PP931 - PP934 14PP935 - PP936 3PP946 - PP948 14PP951 - PP952 3PP961 - PP965 14PP966 - PP967 3PP981 - PP982 14PP983 - PP987 15PP988 9PP989 - PP990 3PP991 14PP993 3PQ001 - PQ012 GroupVariable Number 14PQ013 - PQ016 3PQ026 - PQ037 14PQ038 - PQ041 3PQ051 - PQ061 14PQ062 - PQ073 9PQ074 - PQ085 3PQ086 14PQ087 - PQ092 3PQ101 - PQ110 14PQ111 - PQ198 15PQ199 15PQ201 - PQ202 14PQ221 - PQ229 9PQ230 14PQ231 - PQ236 9PQ237 14PQ241 - PQ243 14PQ251 - PQ255 15PQ256 - PQ257 9PQ258 - PQ267 14PQ281 - PQ286 15PQ287 9PQ288 - PQ296 14PQ301 - PQ305 9PQ306 - PQ307 14PQ331 - PQ332 9PQ341 - PQ344 9PQ361 - PQ369 9PQ401 - PQ406 10PQ407 6PQ408 9PQ411 - PQ413 9PQ421 GroupVariable Number 10PQ471 - PQ472 6PQ473 10PQ479 - PQ480 9PQ481 9PQ486 10PQ487 9PQ491 - PQ493 9PQ771 9PQ791 - PQ793 9PQ801 - PQ803 10PQ804 - PQ805 10PQ931 - PQ932 9PS601 - PS616 9PS631 9PS636 - PS638 14PS641 - PS642 9PS643 - PS644 9PS651 - PS657 14PS666 - PS668 9PS669 9PS691 - PS692 9PS701 - PS703 18PS751 - PS762 17PT001 - PT011 5PT021 - PT023 17PT024 - PT027 12PT028 17PT041 - PT059 12PT060 - PT063 8PT064 5PT101 17PT102 - PT105 5PT121 - PT123 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 24 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 25 GroupVariable Number 17PT124 - PT125 5PT146 17PT147 - PT148 17PT161 - PT170 5PT181 - PT182 17PT183 - PT187 5PT211 - PT214 17PT215 - PT220 5PT295 17PT301 - PT303 12PT304 - PT306 17PT331 - PT360 17PT381 - PT399 17PT401 - PT435 12PT436 - PT438 17PT501 - PT512 17PT561 - PT565 17PT581 - PT584 17PT611 - PT621 17PT641 - PT642 17PT651 - PT655 17PT671 - PT672 17PT701 - PT703 19PU001 - PU007 20PU008 - PU025 4PV001 - PV040 16PV041 - PV055 16PV201 - PV202 11PV203 16PV231 - PV237 16PV271 - PV272 16PV281 - PV282 11PV283 GroupVariable Number 4PW001 - PW036 16PW037 - PW050 4PW051 16PW052 - PW054 4PW061 - PW063 16PW064 - PW068 16PW072 4PW091 - PW093 16PW094 16PW101 - PW102 16PW106 4PW111 - PW117 16PW118 - PW120 16PW156 - PW157 4PW161 - PW162 16PW163 - PW167 16PW201 - PW223 11PW224 - PW230 16PW231 - PW240 11PW241 - PW244 7PW245 16PW261 16PW265 - PW268 11PW278 16PW281 7PW282 - PW284 16PW293 16PW296 16PW301 - PW323 11PW324 - PW327 11PW461 - PW467 4PW501 - PW503 16PW504 GroupVariable Number 4PW511 - PW518 16PW519 - PW520 16PW526 4PW531 - PW535 16PW536 - PW545 11PW546 16PW556 11PW557 4PW561 - PW563 16PW564 4PW571 - PW573 16PW574 - PW576 4PW591 - PW594 16PW595 - PW596 4PW611 - PW615 16PW616 - PW620 4PW631 - PW632 16PW633 - PW634 4PW661 16PW662 16PW681 - PW683 16PW701 - PW702 16PW711 - PW717 16PW741 - PW742 16PW761 16PW771 26PX071 26PX701 26PY001 - PY008 26PY021 1PY022 26PY031 1PY036 - PY037 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 25 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 26 GroupVariable Number 1PY046 - PY048 1PY051 - PY053 1PY056 - PY057 1PY101 - PY103 1PY111 - PY113 1PY131 - PY135 1PY141 - PY143 1PY151 - PY154 1PY156 - PY157 1PY161 - PY162 1PY166 1PY191 1PY201 1PY221 - PY222 GroupVariable Number 1PY231 1PY241 - PY244 1PY270 - PY275 1PY281 1PY286 26PY301 - PY304 26PY321 - PY323 26PY341 - PY346 26PY361 - PY362 26PY381 1PY401 22PY409 - PY410 1PY411 1PY421 - PY422 GroupVariable Number 1PY441 1PY451 1PY461 - PY462 22PY463 22PY591 - PY595 1PY611 - PY612 1PY621 1PY631 1PY651 1PY671 - PY672 22PY721 1PY741 -- -- 2. Spares Affected None. B. Concurrent Requirements None. C. Reason This service bulletin gives instructions for inspection and repair for cracking along the chem-mill steps on the fuselage skin from STA 259.5 to STA 1016. This service bulletin will supersede Service Bulletin (SB) 737-53A1210 Revision 3 and will contain all requirements of SB 737-53A1210 Revision 3 with the exception of lower lobe chem-mill cracking between STA 727 and STA 1016. The lower lobe chem-mill cracking between STA 727 and STA 1016 is the subject of Service Bulletins 737-53-1065 (737-200/-200C), 737-53-1168 (737-300), 737-53-1187 (737-400) and 737-53-1315 (737-500). In addition, this service bulletin was created to expand the Non-Destructive Test (NDT) inspection areas of the skin to all horizontal and vertical chem-mill step locations with a history of cracking between STA 259.5 to STA 1016 and to include the requirements to prevent Widespread Fatigue Damage (WFD) in the fuselage skin due to cracking in the chem-mill steps. Accomplishment of this service bulletin will allow early detection of cracks at the step of the chem-mill pockets and prevent WFD by reducing the chance of multiple adjacent chem-mill step cracks for linking with each other. Continued operation of the airplane with undetected chem-mill steps cracks could result in an uncontrolled decompression of the airplane and loss of structural integrity of the airplane. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 26 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 27 Boeing has received a large number of reports of horizontal and vertical chem-mill step cracks while accomplishing the inspections in accordance with Service Bulletin 737-53A1210. The service history table below provides further descriptions of operator findings. Cracks found at the step of the chem-mill pockets are caused by fatigue from hoop stress and higher than expected bending stresses across the chem-mill steps. Multiple site damage leading to simultaneous chem-mill step cracking in consecutive bays is the source for WFD. The fuselage skin panels with side-by-side chem-mill pockets have been identified to be structure that is susceptible to WFD. Service History ReportFlight Cycles Operators have reported horizontal cracks along the edges of the chem-milled pockets in the skin at S-12 in the bay forward of STA 520 and just above the S-4, S-10, and S-14 lap joints. Horizontal chem-mill line cracks have also been found in non-lap joint areas of the fuselage crown skin and at the tear strap attachments to the fuselage skin. The chem-mill line cracks were up to 8 inches long, and multiple adjacent bays have been found cracked along the same stringer. 23,425 - 64,420 Operators have reported horizontal skin cracks along the edges of the chem-milled pockets in the skin below S-14 in Section 41. The cracks were up to 7.25 inches long. 22,786 - 80,113 Operators have reported circumferential cracks along the vertical chem-mill steps of the fuselage skin next to the STA 360, STA 727, and STA 908 butt joints from S-3R to S-7R. Cracks have been found in multiple adjacent bays and have varied in length from 0.75 inch to 4 inches. 45,100 - 67,400 Boeing Service Related Problems (SRP) 737-SRP-53-0503 and 737-SRP-53-0394 are related to this service bulletin. Boeing Fleet Team Digests (FTD) 737 FTD 53-14004 is related to this service bulletin. D. Description Group 1-5, 9-25: 1. Do the following inspections of the fuselage skin for any crack: a. Do an external detailed and NDT inspection of the fuselage skin from S-10L to S-10R for any vertical crack along the chem-mill step lines just forward and aft of STA 360, STA 540, STA 727, and STA 908 for 737-200/200C/300/500 airplanes and STA 360, STA 500C, BS 540, STA 727, STA 727G and STA 908 for 737-400 airplanes and at known locations. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. b. Do an external detailed or external detailed and NDT inspection for any crack in the fuselage skin from STA 259.5 to STA 360 along the horizontal chem-mill step line. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 27 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 28 c. Do an external detailed or external detailed and NDT inspection for any crack in the fuselage skin from STA 360 to STA 1016 and S-10L to S-10R along the horizontal chem-mill step line. Skin inspection figures given in this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. d. Do an external detailed or external detailed and NDT inspection of the Section 43 lower lobe skin for any crack from S-14 to S-26 left and right from STA 360 to STA 540 along the horizontal chem-mill step line. Skin inspection figures given in this service bulletin show specific areas to inspect for any crack along the chem-mill step line at Section 43 lower lobe. e. Do an external detailed and NDT inspection of the window belt dummy bay locations along the horizontal chem-mill step lines of the fuselage skin from S-10 to S-14 left and right and STA 500D to STA 520 for 737-300 airplanes, STA 500E to STA 500F and STA 500G to STA 520 for 737-400 airplanes and STA 482B to STA 520 for 737-500 airplanes for any crack. f. Do an external detailed and NDT inspection for any horizontal crack along the chem-mill step lines of the fuselage skin from STA 360 to STA 1016 at the lap joints S-4, S-10 and S-14 left and right. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. g. Do an external High Frequency Eddy Current (HFEC) inspection for any crack in the fuselage skin at the tear strap attachments from STA 360 to STA 1016 at the lap joints S-4, S-10 and S-14 left and right. 2. If any crack is found, do the repair in accordance with this service bulletin or contact The Boeing Company for repair instructions and do the repair. 3. If no crack is found, repeat the detailed and NDT inspections at the intervals given in Paragraph 1.E., Compliance. Group 6-8: 1. Do the following inspections of the fuselage skin for any crack: a. Do an external detailed inspection for any crack in the fuselage skin from STA 259.5 to STA 360 along the horizontal chem-mill step line. Skin inspection figures given in the this service bulletin show specific areas to inspect for any crack along the chem-mill step line of the fuselage skin. b. Do an external detailed or external detailed and NDT inspection of the Section 43 lower lobe skin for any crack from S-14 to S-26 left and right from STA 360 to STA 540 along the horizontal chem-mill step line. Skin inspection figures given in this service bulletin show specific areas to inspect for any crack along the chem-mill step line at Section 43 lower lobe. 2. If any crack is found, do the repair in accordance with this service bulletin or contact The Boeing Company for repair instructions and do the repair. 3. If no crack is found, repeat the detailed and NDT inspections at the intervals given in Paragraph 1.E., Compliance. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 28 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 29 Group 26: 1. The Boeing Company endorses the new 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 26 (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. The work in this service bulletin is done in the maintenance zone(s) given below. Group 1, 22: Affected Maintenance Zones ZoneModel 1-1, 1-2, 1-7, 1-8, 2-2, 2-5, 2-8, 2-18737-200C Group 2, 13, 23-24: Affected Maintenance Zones ZoneModel 1-1, 1-2, 1-7, 1-8, 2-2, 2-5, 2-8, 2-18737-200 Group 3, 6, 9-10, 14-15, 18, 21, 25: Affected Maintenance Zones ZoneModel 101, 102, 107, 108, 202, 205, 208, 218737-300 Group 4, 7, 11, 16: Affected Maintenance Zones ZoneModel 101, 102, 107, 108, 202, 205, 208, 218737-400 Group 5, 8, 12, 17, 19-20: Affected Maintenance Zones ZoneModel 101, 102, 107, 108, 202, 205, 208, 218737-500 Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 29 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 30 Group 26: Affected Maintenance Zones ZoneModel 1-1, 1-2, 1-7, 1-8, 2-2, 2-5, 2-8, 2-18737-100, 737-200, 737-200C E. Compliance Federal Aviation Administration (FAA) Airworthiness Directives AD 2009-07-11, AD 2017-20-12, AD 2017-20-14 and AD 2013-18-08 are related to this service bulletin. The effective date of AD 2009-07-11 is May14, 2009, The effective date of AD 2017-20-12 is November 16, 2017, The effective date of AD 2017-20-14 is November 16, 2017, The effective date of AD 2013-18-08 is November 6, 2013. 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. 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. Group 26: The Boeing Company endorses the new 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 26 (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. A logic diagram showing compliance tasks and compliance times is included as an aid in APPENDIX A, APPENDIX B, APPENDIX C, APPENDIX D, APPENDIX E, APPENDIX F, APPENDIX G, APPENDIX H, APPENDIX I, APPENDIX J, APPENDIX K, APPENDIX L, APPENDIX M, APPENDIX N, APPENDIX O, APPENDIX P, APPENDIX Q, APPENDIX R, APPENDIX S, APPENDIX T, APPENDIX U, APPENDIX V and APPENDIX W. Accomplish the required action(s), based on the applicable conditions in Tables 1 through 24, in accordance with Paragraph 3. Accomplishment Instructions. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 30 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 31 Group 1-5, 9-25, Configuration 1: Table 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-10L and S-10R common to the inspection location after 46,999 total flight cycles and have a record of the skin panel re- placement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a window belt skin panel re- placed with a production skin panel common to the inspection location after 49,999 total flight cycles and have a record of the skin panel replacement. -Within 1,800 flight cycles after the accomplishment of the last inspec- tion in accordance with Service Bulletin 737-53A1210. Do PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. (a)(b)(h) All airplanes that have ac- complished at least one in- spection of the horizontal chem-mill steps at the lap joints in accordance with Service Bulletin 737- 53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 31 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 32 Group 1-5, 9-25, Configuration 1: Table 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 7: SRM RE- PAIR. (d) CONDITION 1: ANY CRACK FOUND DURING PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS. 1,800 flight cycles. (a)(b)(c)(g)(h) -OPTION 1 (ACTION 2): Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. -Before further flight.OPTION 2 (ACTION 1): Do PART 8: CATEGORY C REPAIR. (e)(f) 1,800 flight cycles. (a)(b)(c)(g)(h) -OPTION 2 (ACTION 2): Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. -Before further flight.OPTION 3 (ACTION 1): If the repair given in PART 7: SRM REPAIR or PART 8: CATEGORY C REPAIR is not applica- ble, contact The Boeing Company for repair in- structions and do the re- pair. 1,800 flight cycles. (a)(b)(c)(g)(h) -OPTION 3 (ACTION 2): Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 32 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 33 Group 1-5, 9-25, Configuration 1: Table 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition 1,800 flight cycles. (a)(b)(c)(g)(h) -Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. CONDITION 2: NO CRACK FOUND DURING PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS. (a) It is not required to accomplish the PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS under existing repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of either BACR15BB6D rivets, BACR15BB6AD rivets or a combination of the two, on each side of the chem-mill step in the circumferential direction with 5D to 6D fastener spacing; and – The repair or modification is similar to 737-100/200 SRM 53-30-03, Figure 48 or 737-300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53-00- 01, Repair 31 with regard to fastener layout and pitch, part thickness and material, and in- stallation. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 33 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 34 Group 1-5, 9-25, Configuration 1: Table 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition (b) It is not required to inspect the skin at the tear strap tabs under existing external repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners above and below the tear strap tab fasteners that require inspection; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of 3/16 inch diameter fasteners on each side of the inspected area of the tear strap with 5D to 6D fastener spacing; and – The repair or modification is similar to 737-100/200 SRM 53-30-03, Figure 48 or 737-300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53-00- 01, Repair 31 with regard to fastener type, size, layout and pitch, part thickness and mate- rial, and installation. (c) Accomplishment of a skin panel replacement with a production skin panel between S-10L and S-10R after 46,999 total flight cycles terminates the repeat PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS inspections at the replaced skin panel location only. (d) The applicability limitations and post-repair inspection requirements of PART 7: SRM REPAIR are in 737-100/200 SRM 53-30-03, Figure 48 and 737-300 SRM 53-00-01 Repair 31, 737-400 SRM 53-00-01 Repair 31, or 737-500 SRM 53-00-01 Repair 31. (e) The applicability limitations of the Category C repair are in PART 8: CATEGORY C REPAIR. (f) Compliance times for post-repair detailed inspection of the Category C repairs done in accordance with PART 8 are in Paragraph 1.E., Compliance, Table 19. (g) Airplanes that have a window belt skin panel replaced with a production window belt skin panel after 49,999 total flight cycles and have a record of the skin panel replacement, terminates PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS inspections at the replaced skin panel only. (h) Window belt solid skin panels replacement accomplished in accordance with SB 737-53A1177 terminate the PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINT inspections at the replaced skin panel only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 34 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 35 Group 1-5, 9-25, Configuration 2: Table 2: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-10L and S-10R common to the inspection location after 46,999 total flight cycles and have a record of the skin panel re- placement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a window belt skin panel re- placed with a production skin panel common to the inspection location after 49,999 total flight cycles and have a record of the skin panel replacement. -Within 1,800 flight cycles af- ter November 6, 2013 Before the times specified in Ta- ble 24: Inspec- tion Threshold for any crack at Chem-Mill Steps Common to Lap Joints. Do PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. (a)(b)(h) All airplanes that have not previously inspected the horizontal chem-mill steps at the lap joints in accor- dance with Service Bulletin 737-53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 35 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 36 Group 1-5, 9-25, Configuration 2: Table 2: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 7: SRM RE- PAIR. (d) CONDITION 1: ANY CRACK FOUND DURING PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS. 1,800 flight cycles. (a)(b)(c)(g)(h) -OPTION 1 (ACTION 2): Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. -Before further flight.OPTION 2 (ACTION 1): Do PART 8: CATEGORY C REPAIR. (e)(f) 1,800 flight cycles. (a)(b)(c)(g)(h) -OPTION 2 (ACTION 2): Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. -Before further flight.OPTION 3 (ACTION 1): If the repair given in PART 7: SRM REPAIR or PART 8: CATEGORY C REPAIR is not applica- ble, contact The Boeing Company for repair in- structions and do the re- pair. 1,800 flight cycles. (a)(b)(c)(g)(h) -OPTION 3 (ACTION 2): Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 36 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 37 Group 1-5, 9-25, Configuration 2: Table 2: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition 1,800 flight cycles. (a)(b)(c)(g)(h) -Repeat PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM- MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS for any crack. CONDITION 2: NO CRACK FOUND DURING PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS. (a) It is not required to accomplish the PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS under existing repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of either BACR15BB6D rivets, BACR15BB6AD rivets or a combination of the two, on each side of the chem-mill step in the circumferential direction with 5D to 6D fastener spacing; and – The repair or modification is similar to 737-100/200 SRM 53-30-03, Figure 48 or 737-300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53-00- 01, Repair 31 with regard to fastener layout and pitch, part thickness and material, and in- stallation. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 37 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 38 Group 1-5, 9-25, Configuration 2: Table 2: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition (b) It is not required to inspect the skin at the tear strap tabs under existing external repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners above and below the tear strap tab fasteners that require inspection; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of 3/16 inch diameter fasteners on each side of the inspected area of the tear strap with 5D to 6D fastener spacing; and – The repair or modification is similar to 737-100/200 SRM 53-30-03, Figure 48 or 737-300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53-00- 01, Repair 31 with regard to fastener type, size, layout and pitch, part thickness and mate- rial, and installation. (c) Accomplishment of a skin panel replacement with a production skin panel from S-10L to S-10R after 46,999 total flight cycles terminates the repeat PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS inspections at the replaced skin panel location only. (d) The applicability limitations and post-repair inspection requirements of PART 7: SRM REPAIR are in 737-100/200 SRM 53-30-03, Figure 48 and 737-300 SRM 53-00-01 Repair 31, 737-400 SRM 53-00-01 Repair 31, or 737-500 SRM 53-00-01 Repair 31. (e) The applicability limitations of the Category C repair are in PART 8: CATEGORY C REPAIR. (f) Compliance times for post-repair detailed inspection of the Category C repair done in accordance with PART 8 are in Paragraph 1.E., Compliance, Table 19. (g) Airplanes that have a window belt skin panel replaced with a production window belt skin panel after 49,999 total flight cycles and have a record of the skin panel replacement, terminates PART 1: INSPEC- TION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS inspections at the replaced skin panel only. (h) Window belt solid skin panels replacement accomplished in accordance with SB 737-53A1177 terminate the PART 1: INSPECTION OF THE SKIN HORIZONTAL CHEM-MILL STEPS AND THE TEAR STRAP TABS AT THE LAP JOINTS inspections at the replaced skin panel only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 38 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 39 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 1: Table 3: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a window belt skin panel re- placed with a production skin panel common to the inspection location after 49,999 total flight cycles and have a record of the skin panel replacement. -Within 1,800 flight cycles after the accomplishment of the last inspec- tion in accordance with Service Bulletin 737-53A1210. Do PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. (a)(c)(d)(f) All airplanes that have ac- complished at least one in- spection of the horizontal chem-mill step cracks in the window belt area from STA 500D to STA 520 for 737-300 or from STA 482B to STA 520 for 737-500 in accordance with Service Bulletin 737-53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 39 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 40 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 1: Table 3: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 12: REPAIR FOR STRINGER 12 CHEM-MILL CRACKS. (b) CONDITION 3: ANY CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 1 (ACTION 2): Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. -Within 43,000 flight cycles after the accomplishment of PART 12: REPAIR FOR STRINGER 12 CHEM MILL CRACKS. OPTION 1 (ACTION 3): Do PART 13: POST-RE- PAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF THE STRINGER 12 CHEM- MILL CRACK REPAIR for any crack. -Before further flight.OPTION 2 (ACTION 1): If the repair given in PART 12: REPAIR FOR STRINGER 12 CHEM- MILL CRACKS is not ap- plicable, contact The Boeing Company for re- pair instructions and do the repair. 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 2 (ACTION 2): Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. -Before further flightContact The Boeing Company for repair in- structions and do the re- pair. CONDITION 4: ANY CRACK FOUND DURING PART 13: POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) IN- SPECTION OF THE STRINGER 12 CHEM- MILL CRACK REPAIR. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 40 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 41 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 1: Table 3: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition 3,500 flight cycles.-Repeat PART 13: POST- REPAIR LOW FREQUEN- CY EDDY CURRENT (LFEC) INSPECTION OF THE STRINGER 12 CHEM-MILL CRACK RE- PAIR for any crack. CONDITION 5: NO CRACK FOUND DURING PART 13: POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) IN- SPECTION OF THE STRINGER 12 CHEM- MILL CRACK REPAIR. 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 1: Repeat PART 2: INSPECTION OF THE HORIZONTAL CHEM- MILL STEPS AT THE WINDOW BELT for any crack. CONDITION 6: NO CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. -Before further flightOPTION 2 (ACTION 1): Do PART 11: PREVEN- TIVE MODIFICATION TO THE STRINGER 12 CHEM-MILL STEPS. (g) 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 2 (ACTION 2): Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. (a) It is not required to accomplish the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT under the existing repair or modification doublers provided the installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step. (b) PART 12: REPAIR FOR STRINGER 12 CHEM-MILL CRACKS repair is only applicable for crack findings at chem-mill steps common to stringer 12. (c) Accomplishment of the skin chem-mill steps crack at stringer 12 repair in accordance with Service Bulletin 737-53A1210 or accomplishment of PART 12: REPAIR FOR STRINGER 12 CHEM-MILL CRACKS in accordance with this Service Bulletin terminates the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections of chem-mill steps common to stringer 12 only. (d) Accomplishment of preventive modification to the stringer 12 chem-mill steps in accordance with Service Bulletin 737-53A1210 or accomplishment of PART 11: PREVENTIVE MODIFICATION TO THE STRINGER 12 CHEM-MILL STEPS in accordance with this Service Bulletin terminates the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections common to stringer 12 only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 41 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 42 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 1: Table 3: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition (e) Accomplishment of the window belt skin panel replacement with a production skin panel after 49,999 total flight cycles terminates the repeat PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. (f) Window belt solid skin panels replacement accomplished in accordance with Service Bulletin 737-53A1177 terminate the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. (g) The applicability limitation of the preventive modification are in PART 11: PREVENTIVE MODIFICATION TO THE STRINGER 12 CHEM-MILL STEPS. Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 2: Table 4: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a window belt skin panel re- placed with a production skin panel common to the inspection location after 49,999 total flight cycles and have a record of the skin panel replacement. -Within 1,800 flight cycles af- ter November 6, 2013. Before 25,000 total flight cy- cles. Do PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. (a)(c)(d)(f) All airplanes that have not previously inspected the horizontal chem-mill step in the window belt area from STA 500D to STA 520 for 737-300 or from STA 482B to STA 520 for 737- 500 in accordance with Service Bulletin 737- 53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 42 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 43 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 2: Table 4: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 12: REPAIR FOR STRINGER 12 CHEM-MILL CRACKS for any crack (b) CONDITION 3: ANY CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 1 (ACTION 2): Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. -Within 43,000 flight cycles after the accomplishment of PART 12: REPAIR FOR STRINGER 12 CHEM MILL CRACKS. OPTION 1 (ACTION 3): Do PART 13: POST-RE- PAIR LOW FREQUENCY EDDY CURRENT (LFEC) INSPECTION OF THE STRINGER 12 CHEM- MILL CRACK REPAIR for any crack. -Before further flight.OPTION 2 (ACTION 1): If the repair given in PART 12: REPAIR FOR STRINGER 12 CHEM- MILL CRACKS is not ap- plicable, contact The Boeing Company for re- pair instructions and do the repair. 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 2 (ACTION 2): Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. -Before further flightContact The Boeing Company for repair in- structions and do the re- pair. CONDITION 4: ANY CRACK FOUND DURING PART 13: POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) IN- SPECTION OF THE STRINGER 12 CHEM- MILL CRACK REPAIR. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 43 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 44 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 2: Table 4: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition 3,500 flight cycles.-Repeat PART 13: POST- REPAIR LOW FREQUEN- CY EDDY CURRENT (LFEC) INSPECTION OF THE STRINGER 12 CHEM-MILL CRACK RE- PAIR for any crack. CONDITION 5: NO CRACK FOUND DURING PART 13: POST-REPAIR LOW FREQUENCY EDDY CURRENT (LFEC) IN- SPECTION OF THE STRINGER 12 CHEM- MILL CRACK REPAIR. 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 1: Repeat PART 2: INSPECTION OF THE HORIZONTAL CHEM- MILL STEPS AT THE WINDOW BELT for any crack. CONDITION 6: NO CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. -Before further flightOPTION 2 (ACTION 1): Do PART 11: PREVEN- TIVE MODIFICATION TO THE STRINGER 12 CHEM-MILL STEPS. (g) 1,800 flight cycles. (a)(c)(d)(e)(f) -OPTION 2 (ACTION 2): Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. (a) It is not required to accomplish the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT under the existing repair or modification doublers provided the installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step. (b) PART 12: REPAIR FOR STRINGER 12 CHEM-MILL CRACKS repair is only applicable for crack findings at chem-mill steps common to stringer 12. (c) Accomplishment of the skin chem-mill steps crack at stringer 12 repair in accordance with Service Bulletin 737-53A1210 or accomplishment of PART 12: REPAIR FOR STRINGER 12 CHEM-MILL CRACKS in accordance with this Service Bulletin terminates the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections of chem-mill steps common to stringer 12 only. (d) Accomplishment of preventive modification to the stringer 12 chem-mill steps in accordance with Service Bulletin 737-53A1210 or accomplishment of PART 11: PREVENTIVE MODIFICATION TO THE STRINGER 12 CHEM-MILL STEPS in accordance with this Service Bulletin terminates the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections common to stringer 12 only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 44 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 45 Group 3, 5, 9-10, 12, 14-15, 17-21, 25, Configuration 2: Table 4: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition (e) Accomplishment of the window belt skin panel replacement with a production skin panel after 49,999 total flight cycles terminates the repeat PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. (f) Window belt solid skin panels replacement accomplished in accordance with Service Bulletin 737-53A1177 terminate the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. (g) The applicability limitation of the preventive modification are in PART 11: PREVENTIVE MODIFICATION TO THE STRINGER 12 CHEM-MILL STEPS. Group 4, 11, 16, Configuration 1: Table 5: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a window belt skin panel re- placed with a production skin panel common to the inspection location after 49,999 total flight cycles and have a record of the skin panel replacement. -Within 1,800 flight cycles after the accomplishment of the last inspec- tion in accordance with Service Bulletin 737-53A1210. Do PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. (a) All airplanes that have ac- complished at least one in- spection of the horizontal chem-mill step cracks in the window belt area from STA 500E to STA 500F and STA 500G to STA 520 in accordance with Service Bulletin 737-53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 45 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 46 Group 4, 11, 16, Configuration 1: Table 5: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Before further flight.CONDITION 3 (ACTION 1): Contact The Boeing Company for repair in- structions and do the re- pair. CONDITION 3: ANY CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. 1,800 flight cycles. (a)(b) -CONDITION 3 (ACTION 2): Repeat PART 2: IN- SPECTION OF THE HORIZONTAL CHEM- MILL STEPS AT THE WINDOW BELT for any crack. 1,800 flight cycles. (a)(b) -Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. CONDITION 6: NO CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. (a) It is not required to accomplish the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT under the existing repair or modification doublers provided the installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step. (b) Accomplishment of the window belt skin panel replacement with a production skin panel after 49,999 total flight cycles terminates the repeat PART 2 : INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. Group 4, 11, 16, Configuration 2: Table 6: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a window belt skin panel re- placed with a production skin panel common to the inspection location after 49,999 total flight cycles and have a record of the skin panel replacement. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 46 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 47 Group 4, 11, 16, Configuration 2: Table 6: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Within 1,800 flight cycles af- ter November 6, 2013. Before 25,000 total flight cy- cles. Do PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. (a) All airplanes that have not previously inspected the horizontal chem-mill step in the window belt area from STA 500E to STA 500F and STA 500G to STA 520 in accordance with Service Bulletin 737- 53A1210. -Before further flight.CONDITION 3 (ACTION 1): Contact The Boeing Company for repair in- structions and do the re- pair. CONDITION 3: ANY CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. 1,800 flight cycles. (a)(b) -CONDITION 3 (ACTION 2): Repeat PART 2: IN- SPECTION OF THE HORIZONTAL CHEM- MILL STEPS AT THE WINDOW BELT for any crack. 1,800 flight cycles. (a)(b) -Repeat PART 2: INSPEC- TION OF THE HORIZON- TAL CHEM-MILL STEPS AT THE WINDOW BELT for any crack. CONDITION 6: NO CRACK FOUND DURING PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT. (a) It is not required to accomplish the PART 2: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT under the existing repair or modification doublers provided the installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step. (b) Accomplishment of the window belt skin panel replacement with a production skin panel after 49,999 total flight cycles terminates the repeat PART 2 : INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 47 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 48 Group 1-2, 13, 22-24, Configuration 1: Table 7: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-10L and S-10R common to the inspection location after 46,999 total flight cycles and have a record of the skin panel re- placement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel replacement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 41 skin panel S-19R to S- 24R and from STA 259.5 to STA 360 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel re- placement. -Within 1,800 flight cycles after the accomplishment of the last inspec- tion in accordance with Service Bulletin 737-53A1210. Do PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. (a)(e) All airplanes that have ac- complished at least one in- spection of the vertical chem-mill steps in accor- dance with Service Bulletin 737-53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 48 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 49 Group 1-2, 13, 22-24, Configuration 1: Table 7: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 7: SRM RE- PAIR. (d) CONDITION 7: ANY CRACK FOUND DURING PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. 1,800 flight cycles.(a)(b)(c)(e)(f)(g)-OPTION 1 (ACTION 2):Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. -Before further flight.OPTION 2 (ACTION 1): If the repair given in PART 7: SRM REPAIR is not applicable, contact The Boeing Company for repair instructions and do the repair. 1,800 flight cycles. (a)(b)(c)(e)(f)(g) -OPTION 2 (ACTION 2): Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. 1,800 flight cycles. (a)(b)(c)(e)(f)(g) -Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. CONDITION 8: NO CRACK FOUND DURING PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. (a) It is not required to accomplish PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS under existing repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of 3/16 inch diameter fasteners on each side of the chem-mill step in the longitudinal direction with 5D to 6D fastener spacing; and – The repair or modification is similar to 737-100/200 SRM 53-30-03, Figure 48 with regard to fastener type, size, layout and pitch, part thickness and material, and installation. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 49 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 50 Group 1-2, 13, 22-24, Configuration 1: Table 7: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition (b) Accomplishment of PART 7: SRM REPAIR terminates the repeat PART 3: INSPECTION OF THE VER- TICAL CHEM-MILL STEPS inspections under the SRM repair location only. (c) Accomplishment of a skin panel replacement with a production skin panel between S-10L and S-10R after 46,999 total flight cycles terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS inspections at the replaced skin panel location only. (d) The applicability limitations and post-repair inspection requirements of PART 7: SRM REPAIR are in 737-100/200 SRM 53-30-03, Figure 48. (e) Window belt solid skin panels replacement accomplished in accordance with Service Bulletin 737-53A1177 terminate the PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (f) Airplanes that have a Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (g) Airplanes that have a Section 41 skin panel S-19R to S-24R and from STA 259.5 to STA 360 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS requirement at the replaced skin panel only. Group 1-2, 13, 22-24, Configuration 2: Table 8: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-10L and S-10R common to the inspection location after 46,999 total flight cycles and have a record of the skin panel re- placement. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 50 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 51 Group 1-2, 13, 22-24, Configuration 2: Table 8: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel replacement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 41 skin panel S-19R to S- 24R and from STA 259.5 to STA 360 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel re- placement. -Within 1800 flight cycles af- ter November 6, 2013. Before 55,000 total flight cycles or 55,000 total flight hours whichever oc- curs first. Do PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. (a)(e) All airplanes that have not previously inspected the vertical chem-mill steps in accordance with Service Bulletin 737-53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 51 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 52 Group 1-2, 13, 22-24, Configuration 2: Table 8: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 7: SRM RE- PAIR. (d) CONDITION 7: ANY CRACK FOUND DURING PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. 1,800 flight cycles.(a)(b)(c)(e)(f)(g)-OPTION 1 (ACTION 2):Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. -Before further flight.OPTION 2 (ACTION 1): If the repair given in PART 7: SRM REPAIR is not applicable, contact The Boeing Company for repair instructions and do the repair. 1,800 flight cycles. (a)(b)(c)(e)(f)(g) -OPTION 2 (ACTION 2): Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. 1,800 flight cycles. (a)(b)(c)(e)(f)(g) -Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. CONDITION 8: NO CRACK FOUND DURING PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. (a) It is not required to accomplish PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS under existing repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of 3/16 inch diameter fasteners on each side of the chem-mill step in the longitudinal direction with 5D to 6D fastener spacing; and – The repair or modification is similar to 737-100/200 SRM 53-30-03, Figure 48 with regard to fastener type, size, layout and pitch, part thickness and material, and installation. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 52 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 53 Group 1-2, 13, 22-24, Configuration 2: Table 8: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition (b) Accomplishment of PART 7: SRM REPAIR terminates the repeat PART 3: INSPECTION OF THE VER- TICAL CHEM-MILL STEPS inspections under the SRM repair location only. (c) Accomplishment of a skin panel replacement with a production skin panel between S-10L and S-10R after 46,999 total flight cycles terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS at the replaced skin panel location only. (d) The applicability limitations and post-repair inspection requirements of PART 7: SRM REPAIR are in 737-100/200 SRM 53-30-03, Figure 48. (e) Window belt solid skin panels replacement accomplished in accordance with Service Bulletin 737-53A1177 terminate the PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (f) Airplanes that have a Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (g) Airplanes that have a Section 41 skin panel S-19R to S-24R and from STA 259.5 to STA 360 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. Group 3-5, 9-12, 14-21, 25, Configuration 1: Table 9: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-10L and S-10R common to the inspection location after 46,999 total flight cycles and have a record of the skin panel re- placement. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 53 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 54 Group 3-5, 9-12, 14-21, 25, Configuration 1: Table 9: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel replacement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 41 skin panel S-19R to S- 24R and from STA 259.5 to STA 360 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel re- placement. -Within 1,800 flight cycles after the accomplishment of the last inspec- tion in accordance with Service Bulletin 737-53A1210. Do PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. (a)(e) All airplanes that have ac- complished at least one in- spection of the vertical chem-mill steps in accor- dance with Service Bulletin 737-53A1210. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 54 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 55 Group 3-5, 9-12, 14-21, 25, Configuration 1: Table 9: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition -Before further flight.OPTION 1 (ACTION 1): Do PART 7: SRM RE- PAIR. (d) CONDITION 9: ANY CRACK FOUND DURING PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. 1,800 flight cycles.(a)(b)(c)(e)(f)(g)(h)-OPTION 1 (ACTION 2):Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. -Before further flight.OPTION 2 (ACTION 1): If the repair given in PART 7: SRM REPAIR is not applicable, contact The Boeing Company for repair instructions and do the repair. 1,800 flight cycles. (a)(b)(c)(e)(f)(g)(h) -OPTION 2 (ACTION 2): Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. -Before further flight.OPTION 1: Do PART 14: PREVENTIVE MODIFICA- TION UNDER THE DORSAL FIN. (i) CONDITION 10: NO CRACK FOUND AT A LO- CATION UNDER THE DORSAL FIN INSPECTED IN ACCORDANCE WITH PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. 1,800 flight cycles. (a)(b)(c)(h) -OPTION 2: Repeat PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS for any crack. 1,800 flight cycles. (a)(b)(c)(e)(f)(g)(h) -Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. CONDITION 11: NO CRACK FOUND AT A LO- CATION NOT UNDER THE DORSAL FIN IN- SPECTED IN ACCOR- DANCE WITH PART 3: IN- SPECTION OF THE VER- TICAL CHEM-MILL STEPS. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 55 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 56 Group 3-5, 9-12, 14-21, 25, Configuration 1: Table 9: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition (a) It is not required to accomplish PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS under existing repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of 3/16 inch diameter fasteners on each side of the chem-mill step in the longitudinal direction with 5D to 6D fastener spacing; and – For an area not common to the dorsal fin area, the repair or modification is similar to 737- 300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53- 00-01, Repair 31 with regard to fastener type, size, layout and pitch, part thickness and material, and installation. – For an area common to the dorsal fin area, the repair or modification is similar to 737-300 SRM 53-60-01, Repair 9, or Repair 14, or Repair 15 or 737-400 SRM 53-60-01, Repair 9, or Repair 14, or Repair 15 or 737-500 SRM 53-60-01, Repair 9, or Repair 14, or Repair 15 with regard to fastener type, size, layout and pitch, part thickness and material, and instal- lation. (b) Accomplishment of the PART 7: SRM REPAIR terminates the repeat PART 3 inspections under the SRM repair location only. (c) Accomplishment of a skin panel replacement with a production skin panel between S-10L and S-10R after 46,999 total flight cycles terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS inspections at the replaced skin panel location only. (d) The applicability limitations and post-repair inspection requirements of PART 7: SRM REPAIR are in PART 7: SRM REPAIR and 737-300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53-00-01, Repair 31, or 737-300 SRM 53-60-01, Repair 15 or 737-400 SRM 53-60-01, Repair 15 or 737-500 SRM 53-60-01, Repair 15. (e) Window belt solid skin panels replacement accomplished in accordance with Service Bulletin 737-53A1177 terminate the PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (f) Airplanes that have a Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 56 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 57 Group 3-5, 9-12, 14-21, 25, Configuration 1: Table 9: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition (g) Airplanes that have a Section 41 skin panel S-19R to S-24R and from STA 259.5 to STA 360 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (h) Accomplishment of PART 14: PREVENTIVE MODIFICATION UNDER THE DORSAL FIN terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections requirements under the modification location only. (i) The applicability limitations and post-repair inspection requirements of PART 14: PREVENTIVE MODIFI- CATION UNDER THE DORSAL FIN are in 737-300 SRM 53-60-01, Repair 14 and Repair 15 or 737-400 SRM 53-60-01, Repair 14 and Repair 15 or 737-500 SRM 53-60-01, Repair 14 and Repair 15. Group 3-5, 9-12, 14-21, 25, Configuration 2: Table 10: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-10L and S-10R common to the inspection location after 46,999 total flight cycles and have a record of the skin panel re- placement. --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel replacement. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 57 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 58 Group 3-5, 9-12, 14-21, 25, Configuration 2: Table 10: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have Section 41 skin panel S-19R to S- 24R and from STA 259.5 to STA 360 replaced with a production skin panel common to the inspection location after 39,999 total flight cycles and have a record of the skin panel re- placement. -Within 1,800 flight cycles af- ter November 6, 2013. Before 55,000 total flight cycles or 55,000 total flight hours whichever oc- curs first. Do PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. (a)(e) All airplanes that have not previously inspected the vertical chem-mill steps in accordance with Service Bulletin 737-53A1210. -Before further flight.OPTION 1 (ACTION 1): Do PART 7: SRM RE- PAIR. (d) CONDITION 9: ANY CRACK FOUND DURING PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. 1,800 flight cycles.(a)(b)(c)(e)(f)(g)(h)-OPTION 1 (ACTION 2):Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. -Before further flight.OPTION 2 (ACTION 1): If the repair given in PART 7: SRM REPAIR is not applicable, contact The Boeing Company for repair instructions and do the repair. 1,800 flight cycles. (a)(b)(c)(e)(f)(g)(h) -OPTION 2 (ACTION 2): Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 58 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 59 Group 3-5, 9-12, 14-21, 25, Configuration 2: Table 10: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition -Before further flight.OPTION 1: Do PART 14: PREVENTIVE MODIFICA- TION UNDER THE DORSAL FIN. (i) CONDITION 10: NO CRACK FOUND AT A LO- CATION UNDER THE DORSAL FIN INSPECTED IN ACCORDANCE WITH PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS. 1,800 flight cycles. (a)(b)(c)(h) -OPTION 2: Repeat PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS for any crack. 1,800 flight cycles. (a)(b)(c)(e)(f)(g)(h) -Repeat PART 3: INSPEC- TION OF THE VERTICAL CHEM-MILL STEPS for any crack. CONDITION 11: NO CRACK FOUND AT A LO- CATION NOT UNDER THE DORSAL FIN IN- SPECTED IN ACCOR- DANCE WITH PART 3: IN- SPECTION OF THE VER- TICAL CHEM-MILL STEPS. (a) It is not required to accomplish PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS under existing repair or modification doublers provided either: 1. The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings, and the installed repair or modification extends a minimum of three rows of fasteners on each side of the chem-mill step; or 2. The external repair or modification doubler satisfies the following: – The installed repair or modification was approved by the FAA or by a Boeing Company authorized representative who was authorized by the FAA to make such findings; and – The repair or modification extends a minimum of two rows of 3/16 inch diameter fasteners on each side of the chem-mill step in the longitudinal direction with 5D to 6D fastener spacing; and – For an area not common to the dorsal fin area, the repair or modification is similar to 737- 300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53- 00-01, Repair 31 with regard to fastener type, size, layout and pitch, part thickness and material, and installation. – For an area common to the dorsal fin area, the repair or modification is similar to 737-300 SRM 53-60-01, Repair 9, or Repair 14, or Repair 15 or 737-400 SRM 53-60-01, Repair 9, or Repair 14, or Repair 15 or 737-500 SRM 53-60-01, Repair 9, or Repair 14, or Repair 15 with regard to fastener type, size, layout and pitch, part thickness and material, and instal- lation. (b) Accomplishment of the PART 7: SRM REPAIR terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections under the SRM repair location only. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 59 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT ### Page 60 Group 3-5, 9-12, 14-21, 25, Configuration 2: Table 10: INSPECTION OF THE VERTICAL CHEM-MILL STEPS FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance Time (Whichever Occurs Later) ActionCondition (c) Accomplishment of a skin panel replacement with a production skin panel between S-10L and S-10R after 46,999 total flight cycles terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM- MILL STEPS inspections at the replaced skin panel location only. (d) The applicability limitations and post-repair inspection requirements of PART 7: SRM REPAIR are in PART 7: SRM REPAIR and 737-300 SRM 53-00-01, Repair 31 or 737-400 SRM 53-00-01, Repair 31 or 737-500 SRM 53-00-01, Repair 31, or 737-300 SRM 53-60-01, Repair 15 or 737-400 SRM 53-60-01, Repair 15 or 737-500 SRM 53-60-01, Repair 15. (e) Window belt solid skin panels replacement accomplished in accordance with Service Bulletin 737-53A1177 terminate the PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS AT THE WINDOW BELT inspections at the replaced skin panel only. (f) Airplanes that have a Section 43 lower lobe skin panel from S-14R to S-19R and from STA 360 to STA 540 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (g) Airplanes that have a Section 41 skin panel S-19R to S-24R and from STA 259.5 to STA 360 replaced with a production skin panel after 39,999 total flight cycles and have a record of the skin panel replacement, terminates PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections at the replaced skin panel only. (h) Accomplishment of PART 14: PREVENTIVE MODIFICATION UNDER THE DORSAL FIN terminates the repeat PART 3: INSPECTION OF THE VERTICAL CHEM-MILL STEPS inspections requirements under the modification location only. (i) The applicability limitations and post-repair inspection requirements of PART 14: PREVENTIVE MODIFI- CATION UNDER THE DORSAL FIN are in 737-300 SRM 53-60-01, Repair 9, Repair 14 and Repair 15 or 737-400 SRM 53-60-01, Repair 9, Repair 14 and Repair 15 or 737-500 SRM 53-60-01, Repair 9, Repair 14 and Repair 15. Group 1-25, Configuration 1: Table 11: INSPECTION OF THE HORIZONTAL CHEM-MILL STEPS IN SECTION 43 LOWER LOBE FOR ANY CRACK Repeat Interval (Not to Exceed) Compliance TimeActionCondition --No further action required in accordance with this service bulletin for the re- placed skin panel. Airplanes that have had a skin panel replaced with a production skin panel be- tween S-14 and S-26 com- mon to the inspection loca- tion after 39,999 total flight cycles and have a record of the skin panel replace- ment. Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: March 27, 2020 737-53A1346 60 of 801 BOEING SERVICE BULLETIN 737-53A1346 ALERTALERT The text continues at https://openairdocs.org/service-documents/boeing/737-53a1346/file/eb58e2410e57.md?from=61 --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain, except the copies of manufacturers’ service documents, which belong to their rights holders.