### Commercial **Airplanes** 

# 747 Service Bulletin **ALERT Number: 747-53A2371**  Original Issue: July 29, 1993 Revision 2: December 11, 2012 ATA System: 5300 **SUBJECT:** FUSELAGE - Center Section - STA 780 to STA 940 Upper Deck Tension Tie Inspection, Repair, and Modification 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. 9E991 ECCN: 

## BOEING PROPRIETARY, CONFIDENTIAL AND/OR TRADE SECRET Copyright © 1993 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 Unpublished Work.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, DreamlinerTM, BBJ, DC-8, DC-9, DC-10, KC-10, KDC-10, MD-10, MD-11, MD-80, MD-88, MD-90, P-8A, 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. BOEING is a trademark of Boeing Management Company.

Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 1 of 59 4.0Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 2 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**

BLANK PAGE**Table of Contents** Revision Transmittal Sheet............................................ 5 Summary...................................................... 7 1. PLANNING INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 A. Effectivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1. Airplanes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2. Spares Affected. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 B. Concurrent Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 C. Reason. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 D. Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 E. Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 F. Approval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 G. Manpower. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 H. Weight and Balance Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 I. Electrical Load Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 J. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 1. Existing Data:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2. Data Supplied with this Service Bulletin:. . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3. Installation Drawings Used in the Preparation of this Service Bulletin:. . . . . . . . . . . 23 K. Publications Affected. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 L. Interchangeability and Intermixability of Parts. . . . . . . . . . . . . . . . . . . . . . . . . . . 23 M. Software Accomplishment Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2. MATERIAL INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 A. Material - Price and Availability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 B. Industry Support Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 C. Parts Necessary for Each Airplane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 1. Kits/Parts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2. Parts and Materials Supplied by the Operator. . . . . . . . . . . . . . . . . . . . . . . . 25 3. Parts Modified and Reidentified. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4. Parts Removed and Not Replaced. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 D. Parts Necessary to Change Spares. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 E. Special Tooling - Price and Availability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 F. Special Tooling Necessary to do this Service Bulletin. . . . . . . . . . . . . . . . . . . . . . . 26 3. ACCOMPLISHMENT INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 A. GENERAL INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 B. WORK INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 FIGURE 1: THIS FIGURE IS DELETED (REVISION 2). . . . . . . . . . . . . . . . . . . . . . . . . . 31 FIGURE 2: TENSION TIE DETAILED INSPECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . 32 FIGURE 3: REPAIR OR MODIFICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 FIGURE 4: THIS FIGURE IS DELETED (REVISION 2). . . . . . . . . . . . . . . . . . . . . . . . . . 48 FIGURE 5: THIS FIGURE IS DELETED (REVISION 2). . . . . . . . . . . . . . . . . . . . . . . . . . 49 FIGURE 6: AFTER MODIFICATION INSPECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 FIGURE 7: REPAIR STRAP FABRICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 FIGURE 8: TENSION TIE HIGH FREQUENCY EDDY CURRENT INSPECTION. . . . . . . . . . . . 55 APPENDIX A: FLIGHT SAFETY SECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 3 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 4 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**

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### Commercial **Airplanes** 

# 747 Service Bulletin **ALERT Revision Transmittal Sheet**  **Number: 747-53A2371** Original Issue: July 29, 1993 Revision 2: December 11, 2012 ATA System: 5300 **SUBJECT:** FUSELAGE - Center Section - STA 780 to STA 940 Upper Deck Tension Tie Inspection, Repair, and Modification This revision includes all pages of the service bulletin. **COMPLIANCE INFORMATION RELATED TO THIS REVISION** More work is necessary on airplanes changed as given in the original issue or Revision 1 of this of this service bulletin. If the modification given in this service bulletin has not previously been done on all affected tension ties, then Boeing recommends that the modification be done at the time given in Paragraph 1.E., Compliance. In addition, Boeing also recommends that operators do a surface high frequency eddy current (HFEC) inspection of the unmodified aft tension tie channels during the next inspection that is scheduled to be done as given in this service bulletin. Federal Aviation Administration (FAA) Airworthiness Directive AD 94-13-06 is related to this service bulletin. **REASON FOR REVISION** This revision is sent to recommend that operators accomplish the modification given in this service bulletin. These sections were changed: 1. In the Summary: Added new Background information related to the revision. Updated Action section to reflect new requirements. Added industry support information. Revised Summary illustration text to reflect changed actions. 2. In paragraph 1.C., Reason: Added new background information related to the revision. 3. In paragraph 1.D., Description: Updated the action descriptions to reflect new requirements, added "More work" statement, and added affected maintenance zones. 4. In paragraph 1.E., Compliance: Added compliance Tables 1, 2, and 3. In previous revisions of this service bulletin, compliance information was given in Figure 1 and Figure 5. 5. In paragraph 1.F., Approval: Updated standard approval paragraphs and added alternative method of compliance statement for AD 94-13-06. 6. In paragraph 1.J., References: Added new references related to this revision. 7. In paragraph 1.K., Publications Affected: Added statement for damage tolerance inspections.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 5 of 598. In paragraph 2.B., Added Industry Support Information. 9. In paragraph 3.A., General Information: Updated general notes to current requirements. 10. In paragraph 3.B., Work Instructions, PART 1 - Tension Tie Inspection: Added reference to paragraph 1.E. for compliance information. Deleted the option to defer repair of cracked tension tie aft channels if additional eddy current inspections find that parts are crack free in other areas. 11. In paragraph 3.B., Work Instructions, PART 2 - After Modification Inspection Program: Added reference to paragraph 1.E. for compliance information. 12. In paragraph 3.B., Work Instructions, PART 4 and PART 5: These new sections have been added. 13. Figure 1: This figure (logic diagram) has been deleted. Compliance information is now found in the compliance tables of paragraph 1.E., Compliance. 14. Figure 3: Added example fastener symbol illustration. 15. Figure 4: This figure has been deleted. In previous revisions of this service bulletin, Figure 4 was an inspection needed to defer repair of cracked tension tie aft channels. The option to defer repair of cracked tension ties is no longer allowed. 16. Figure 5: This figure (logic diagram) has been deleted. Compliance information is now found in the compliance tables of paragraph 1.E., Compliance. 17. Figure 8: This new figure is added for high frequency eddy current inspection. 18. Appendix A: This appendix has been updated to reflect revised compliance information. Vertical lines are put on the left edge of each page, except in Paragraph 1.A., Effectivity, to show the location of important changes. Pages with no vertical lines have no important changes. **REVISION HISTORY** July 29, 1993 Original Issue: April 27, 1995 Revision 1: December 11, 2012 Revision 2:

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 6 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**

### Commercial **Airplanes** 

# 747 Service Bulletin **ALERT Summary**  **Number: 747-53A2371** Original Issue: July 29, 1993 Revision 2: December 11, 2012 ATA System: 5300 **SUBJECT:** FUSELAGE - Center Section - STA 780 to STA 940 Upper Deck Tension Tie Inspection, Repair, and Modification THIS BULLETIN 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 SERVICE BULLETIN TO THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS SERVICE BULLETIN TO THE NEW OWNER. **CONCURRENT REQUIREMENTS** None. **BACKGROUND** This service bulletin gives instructions to do inspections, repairs, and modifications to upper deck tension ties. The affected tension ties are installed from STA 780 to STA 940 aft of the upper deck floor beams. The failure of more than one tension tie can result in rapid depressurization of the airplane. Six operators have reported 47 tension tie cracks on 13 airplanes. Forty-six of the cracks were in the aft channel of the tension tie. Only one crack was in the forward channel of the tension tie. Cracks usually occur in the upper flange of the aft channel of the tension tie. These fatigue cracks occur because the tension ties bend under cabin pressurization loads. Boeing Service Bulletin 747-53-2088 gives instructions to change the STA 760 tension tie on passenger airplanes. That service bulletin also gives instructions to change the STA 780 tension tie on 747-200F airplanes. At line number 204, the tension tie configuration was changed in production. A structural reassessment of the 747 airplane was conducted under the requirements of Federal Aviation Administration (FAA) Advisory Circular 91-56, in accordance with Federal Aviation Regulation (FAR) 25.571 as amended in 1978, to ensure safe operation of 747 airplanes throughout their operational life. From this requirement, the tension ties from STA 780 to 940 were determined to be significant, in that they are critical to airplane structural integrity. The failure of more than one tension tie can result in rapid depressurization of the airplane. Therefore, a flight safety inspection program which will continue throughout the operational life of the airplane is described in this service bulletin. Subsequent to the release of Revision 1 of this service bulletin, the upper deck tension ties have been determined to be structure that could develop Widespread Fatigue Damage (WFD). Due to the concern of WFD in the tension tie structure, Boeing now recommends that operators accomplish the modification given in this service bulletin. Previously, the modification was optional unless a crack was found during an inspection.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 7 of 59For more information about WFD, refer to Boeing Service Letter 747-SL-53-088. Boeing Service Related Problem (SRP) 747-SRP-53-0403 is related to this service bulletin. This table is provided to operators for planning purposes only. Refer to the applicable sections for more information.
**Reference Affected**  **Planning Data** Paragraph 1.A.2., Spares Affected No Spares Affected Paragraph 1.E., Compliance and Paragraph 1.F., Approval Yes AD Related Paragraph 1.H., Weight and Balance Changes Yes Weight and Balance Change Paragraph 1.I., Electrical Load Data No Electrical Load Changed Paragraph 1.K., Publications Affected No Publications Affected Paragraph 1.K., Publications Affected No Airplane Flight Operations Affected (Flight CrewOperations Manual and/or FAA Approved Airplane Flight Manual) Paragraph 2.C.1., Kits/Parts No Boeing supplied Kits/Parts Required Paragraph 2.C.2., Parts and Materials Supplied by the Operator Yes Operator Supplied Material Paragraph 2.F., Special Tooling Necessary to do this Service Bulletin No Special Tooling Required

**ACTION (PRR 85901-120RS)** Do detailed and surface high frequency eddy current (HFEC) inspections for cracks in the outboard ends of each affected tension tie. If cracks are found, repair before any more flights. At tension tie locations where no cracks are found, repeat the inspections until the tension tie is repaired or modified. At tension tie locations that have been repaired or modified, do detailed inspections as given in the After Modification Inspection Program. If cracks are found in a repaired or modified tension tie, contact Boeing for repair instructions. This service bulletin contains a flight safety inspection program. The flight safety inspection program is the minimum inspection program to maintain the structural integrity of the affected area of the airplane. An optional economics based inspection, to be done earlier than the flight safety inspection, would usually be included in this type of service bulletin. However, for this area there is no economics based inspection program. The repair necessary when a crack is found in the flight safety inspection is the same as the repair necessary if a crack is found earlier. **EFFECTIVITY** 747-100/-200B/-200F airplanes. Refer to Paragraph 1.A.1., Airplanes for the list of affected airplanes. **COMPLIANCE** Refer to Paragraph 1.E., Compliance. Federal Aviation Administration (FAA) Airworthiness Directive AD 94-13-06 is related to this service bulletin.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 8 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT INDUSTRY SUPPORT INFORMATION**  This service bulletin was first released before October of 1994. Thus industry support for affected airplanes depends upon whether you ever filed a warranty claim with Boeing on this service bulletin. **MANPOWER Elapsed Hours**  **Total Task Hours Airplanes**  30.5 113.5 Group 1 and 2 27.25 101.25 Group 3 and 7 24 89 Group 4 21 77 Group 5 and 6
**MATERIAL INFORMATION** Operator Supplied Parts/Materials. Refer to Paragraph 2.C., Parts Necessary for Each Airplane.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 9 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 10 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**

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### Commercial **Airplanes** 

# 747 Service Bulletin **ALERT Number: 747-53A2371**  Original Issue: July 29, 1993 Revision 2: December 11, 2012 ATA System: 5300 **SUBJECT:** FUSELAGE - Center Section - STA 780 to STA 940 Upper Deck Tension Tie Inspection, Repair, and Modification THIS BULLETIN 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 SERVICE BULLETIN TO THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS SERVICE BULLETIN TO THE NEW OWNER. **1. PLANNING INFORMATION A. Effectivity**  1. Airplanes This service bulletin is for the airplane(s) shown below. Refer to PRR 85901-120RS for data about this change. Refer to Service Bulletin Index D6-30300 Part 3 for Airplane Variable Number, Line Number, and Serial Number data. **NOTE:** Group 2 airplanes changed as given in Boeing Service Bulletin 747-25-2692, "Equipment/Furnishings - Upper Deck Passenger Compartment Conversion - Upper Deck Extension Station 710 - Station 780 Modification," should be considered Group 3 airplanes for the purposes of this service bulletin.
**DESCRIPTION CONFIGURATION**  **GROUP** 747 airplanes prior to line number 204 with affected tension ties installed from STA 780 to 940. The fasteners used to attach the STA 940 tension tie on Group 1 airplanes is different than on Group 2 airplanes. - 1

747 airplanes prior to line number 204 with affected tension ties installed from STA 780 to 940. The fasteners used to attach the STA 940 tension tie on Group 2 airplanes is different than on Group 1 airplanes. - 2

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 11 of 59**DESCRIPTION CONFIGURATION**  **GROUP** 747 airplanes prior to line number 204, except Group 7 airplanes, with affected tension ties installed only from STA 800 to 940. There is no tension tie at STA 780. - 3

747 airplanes prior to line number 204 with affected tension ties installed only from STA 820 to 940. The tension ties at STA 780 and 800 were removed during a modification at Boeing. - 4

747 airplanes prior to line number 204 with affected tension ties installed only from STA 840 to 940. The tension ties at STA 780, 800, and 820 were removed during a modification at Boeing. The fasteners used to attach the STA 940 tension tie on Group 5 airplanes is different than on Group 6 airplanes. - 5

747 airplanes prior to line number 204 with affected tension ties installed only from STA 840 to 940. The tension ties at STA 780, 800, and 820 were removed during a modification at Boeing. The fasteners used to attach the STA 940 tension tie on Group 6 airplanes is different than on Group 5 airplanes. - 6

747 airplanes prior to line number 204, except Group 3 airplanes, with affected tension ties installed only from STA 800 to STA 940. On 747-200F airplane line number 168, Service Bulletin 747-53-2088 gives instructions to change the STA 780 tension tie. On all other Group 7 airplanes, there is no tension tie at STA 780. - 7

Airplane Models: 747-100, 747-200B, 747-200F **Group Variable Number**  1 RA001 - RA034 1 RA101 - RA115 1 RA161 - RA162 2 RA163 - RA164 1 RA201 - RA203 1 RA216 2 RA217 4 RA245 - RA246 1 RA251 - RA255 2 RA256 - RA261 5 RA301 - RA306

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 12 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Group**  **Variable Number** 6 RA307 - RA308 2 RA309 6 RA310 2 RA311 6 RA312 1 RA351 - RA360 1 RA369 - RA371 2 RA372 - RA373 1 RA401 - RA412 2 RA413 3 RA414 1 RA501 - RA502 1 RA521 - RA523 2 RA524 - RA527 1 RA532 - RA534 2 RA535 - RA540 1 RA551 - RA552 1 RA559 7 RA560 2 RA561 1 RA581 - RA582 2 RA585 1 RA601 - RA602 1 RA631 - RA633 2 RA634 - RA635 1 RA651 - RA652 5 RA671 - RA674 6 RA675 2 RA676 6 RA677 1 RA701 2 RA702 1 RA721

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 13 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Group**  **Variable Number** 7 RA722 3 RA723 - RA724 1 RA741 7 RA742 - RA743 1 RA761 - RA762 1 RA781 3 RA782 1 RA901 - RA916 3 RB001 - RB005 3 RB013 1 RB041 - RB044 2 RB071 - RB075 1 RB101 - RB102 3 RD001 - RD002 7 RR201 2. Spares Affected None. **B. Concurrent Requirements** None. **C. Reason** This service bulletin gives instructions to do inspections, repairs, and modifications to upper deck tension ties. The affected tension ties are installed from STA 780 to STA 940 aft of the upper deck floor beams. The failure of more than one tension tie can result in rapid depressurization of the airplane. Six operators have reported 47 tension tie cracks on 13 airplanes. Forty-six of the cracks were in the aft channel of the tension tie. Only one crack was in the forward channel of the tension tie. Cracks usually occur in the upper flange of the aft channel of the tension tie. These fatigue cracks occur because the tension ties bend under cabin pressurization loads. Boeing Service Bulletin 747-53-2088 gives instructions to change the STA 760 tension tie on passenger airplanes. That service bulletin also gives instructions to change the STA 780 tension tie on 747-200F airplanes.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 14 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**A structural reassessment of the 747 airplane was conducted under the requirements of Federal Aviation Administration (FAA) Advisory Circular 91-56, in accordance with Federal Aviation Regulation (FAR) 25.571 as amended in 1978, to ensure safe operation of 747 airplanes throughout their operational life. From this requirement, the tension ties from STA 780 to 940 were determined to be significant, in that they are critical to airplane structural integrity. The failure of more than one tension tie can result in rapid depressurization of the airplane. Therefore, a flight safety inspection program which will continue throughout the operational life of the airplane is described in this service bulletin. Revision 1 is sent to add references to Federal Aviation Administration (FAA) Airworthiness Directive 94-13-06. Revision 1 is also sent to tell affected operators about airplane group changes. Airplanes RA560, RA742, RA743, and RA722 were moved from Group 1 to Group 7. Airplanes RA723 and RA724 were moved from Group 2 to Group 3. On these airplanes, the tension tie at Station 780 was removed as part of a Boeing modification and replaced with a floor beam. Revision 1 is also sent to add notes that explain the affect of the Boeing Extended Upper Deck conversion on airplane groups. Group 1 airplanes modified by Boeing to the Extended Upper Deck configuration should be considered Group 7 airplanes. Group 2 airplanes modified by Boeing to the Extended Upper Deck configuration should be considered Group 3 airplanes. Revision 1 is also sent to add references to Boeing Service Bulletin 747-25-2692, "Equipment / Furnishings - Upper Deck Passenger Compartment Conversion - Upper Deck Extension Station 710 - Station 780 Modification." As part of the change in Service Bulletin 747-25-2692, the tension tie at Station 780 is removed and replaced with a floor beam. Airplanes changed as given in Service Bulletin 747-25-2692 should be considered Group 3 airplanes. This data was in Notice of Status Change 747-53-2371 NSC 1. Subsequent to the release of Revision 1 of this service bulletin, the upper deck tension ties have been determined to be structure that could develop Widespread Fatigue Damage (WFD). Due to the concern of WFD in the tension tie structure, Boeing now recommends that operators accomplish the modification given in this service bulletin. Previously, the modification was optional unless a crack was found during an inspection. For more information about WFD, refer to Boeing Service Letter 747-SL-53-088. Boeing Service Related Problem (SRP) 747-SRP-53-0403 is related to this service bulletin. Revision 2 is sent to recommend that operators accomplish the modification given in this service bulletin. **D. Description** Do detailed and surface high frequency eddy current (HFEC) inspections for cracks in the outboard ends of each affected tension tie. If cracks are found, repair before any more flights. At tension tie locations where no cracks are found, repeat the inspections until the tension tie is repaired or modified. At tension tie locations that have been repaired or modified, do detailed inspections as given in the After Modification Inspection Program. If cracks are found in a repaired or modified tension tie, contact Boeing for repair instructions. This service bulletin contains a flight safety inspection program. The flight safety inspection program is the minimum inspection program to maintain the structural integrity of the affected area of the airplane. An optional economics based inspection, to be done earlier than the flight safety inspection, would usually be included in this type of service bulletin. However, for this area there is no economics based inspection program. The repair necessary when a crack is found in the flight safety inspection is the same as the repair necessary if a crack is found earlier. At line number 204, the tension tie configuration was changed in production.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 15 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**NOTES: 1. Inspection and maintenance alternatives are given in a diagram in Paragraph 3., ACCOMPLISHMENT INSTRUCTIONS. 2. It is not necessary to count flight-cycles where the cabin differential pressure was below 2.0 psi. 3. The changes specified in Boeing Service Bulletin 747-53-2088, "Frame To Tension Tie Joint Modification - Body Station 760 or 780," can be made on affected airplanes before or during the changes specified in this service bulletin. 4. The change given in Boeing Service Bulletin 747-25-2692, "Equipment/Furnishings - Upper Deck Passenger Compartment Conversion - Upper Deck Extension Station 710 - Station 780 Modification" should be done on affected airplanes before or during the change given in this service bulletin. Service Bulletin 747-25-2692 affects Group 2 airplanes RA526, RA527, RA538, and RA540. 5. If the damaged area is more than the specified limits, repair before any more flights. Contact Boeing for repair instructions. Give the size and location of the damage. When possible, send sketches and photographs. If the damage includes corrosion, send data on the length, width, and largest depth of clean up. SEND TO: BOEING COMMERCIAL AIRPLANE GROUP ATTENTION: MANAGER, AIRLINE SUPPORT Revision 2 - More work is necessary on airplanes changed as given in the original issue or Revision 1 of this of this service bulletin. If the modification given in this service bulletin has not previously been done on all affected airplanes, then Boeing recommends that the modification be done at the time given in Paragraph 1.E., Compliance. In addition, Boeing also recommends that operators do a surface high frequency eddy current (HFEC) inspection of the unmodified aft tension tie channels during the next inspection that is scheduled to be done as given in this service bulletin. The work in this service bulletin is done in the maintenance zone(s) given below. **Group 1-3, 5-6:**
**Affected Maintenance Zones Zone**  **Model** 243, 244 747-100, 747-200B **Group 4:**
**Affected Maintenance Zones Zone**  **Model** 243, 244 747-200B

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 16 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Group 7:** 
**Affected Maintenance Zones Zone**  **Model** 243, 244 747-100, 747-200B, 747-200F **E. Compliance** Federal Aviation Administration (FAA) Airworthiness Directive AD 94-13-06 is related to this service bulletin. For each affected tension tie, accomplish the inspections given in Tables 1 and 3 until modification is accomplished as given in Paragraph 3.B., Work Instructions, PART 5. After modification, accomplish inspections as given in Table 2.**Table 1: Tension Tie Detailed Inspection - (Tension Ties that have not had repair or modification accom plished in accordance with this service bulletin)**  **Repeat Interval (Not to Exceed)**  **Compliance Time (Whichever Occurs Later)**  **Action Condition** 

- - Before the accu- mulation of1,000 flight cycles after July 27, 1994. Do a detailed inspection for cracks in the tension ties as given in paragraph 3.B., Work Instructions, PART 1. (a) (b)Airplanes not previously inspected as given in this service bulletin.

- - Within 3,000 flight cyclesfrom last inspection as given inthis service bulletin.Repeat the detailed inspection for cracks in the tension ties as given inparagraph 3.B., Work Instructions, PART 1. (a) (b)Airplanes previously inspected as given in this service bulletin.

3,000 flight cycles.

- - Repeat the detailed in- spection for cracks in the tension ties as given inparagraph 3.B., Work Instructions, PART 1. (a) (b) No crack found.

- - Before further flight. Repair the tension tie aftchannel as given in paragraph 3.B., Work Instructions, PART 1. (a) (c) Crack found in a tension tie aft channel.

- - Before further flight. Contact Boeing for repair instructions, and do the repair. (c) Crack found in other than a tension tie aft channel.(a) Doing a repair or modification as given in this service bulletin terminates the initial and/or repetitive inspection requirements given in this compliance table.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 17 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Table 1: Tension Tie Detailed Inspection - (Tension Ties that have not had repair or modification accom**  **plished in accordance with this service bulletin) Repeat Interval**  **(Not to Exceed) Compliance Time (Whichever**  **Occurs Later) Action**  **Condition** (b) For Group 1 and 2 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 780 to 940. For Group 3 and 7 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 800 to 940. For Group 5 and 6 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 840 to 940. For Group 4 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 820 to 940. (c) Do repeat inspections at locations where no crack was found. Refer to Table 2 for inspection requirements after repair or modification has been done. **Table 2: Inspection After Repair or Modification Repeat Interval**  **(Not to Exceed) Compliance Time (Whichever**  **Occurs Later) Action**  **Condition**

- - Within 10,000flight cycles after the repair or modification was done asgiven in this service bulletin. Do a detailed inspection for cracks at repaired ormodified tension tie locations as given in paragraph 3.B., Work Instructions, PART 2. (a) (b) Repair or Modification has been done as given in this service bulletin.

- - Before further flight. Contact Boeing for repair instructions, and do the repair. Any crack found.

6,000 flight cycles.

- - Repeat the detailed in-spection for cracks at repaired or modified tension tie locations as given inparagraph 3.B., Work Instructions, PART 2. (a) (b) No crack found.

(a) Group 1 and 2 airplanes, do inspections from STA 780 to 940. Group 3 and 7 airplanes, do inspections from STA 800 to 940. Group 5 and 6 airplanes, do inspections from STA 840 to 940. Group 4 airplanes, do inspections from STA 820 to 940. (b) Additional tension tie inspection requirements are given in Service Bulletin 747-53A2502.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 18 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Table 3: Tension Tie High Frequency Eddy Current Inspection and Modification (Revision 2 - More Work)**  **- (Tension Ties that have not had repair or modification accomplished in accordance with this service bulletin)**  **Repeat Interval (Not to Exceed)**  **Compliance Time (Whichever Occurs Later)**  **Action Condition** 

- Within 3,000flight cycles after the Revision 2 date of this service bulletin. Concurrent withthe next scheduled detailed inspection as given in paragraph1.E., Compliance, Table 1.Do a surface high frequency eddy current (HFEC) inspection for cracks in the tension ties as given in paragraph 3.B., Work Instructions, PART 4. (a) (b) (d) All airplanes.

3,000 flight cycles.

- - Repeat the detailed in- spection for cracks in the tension ties as given inparagraph 3.B., Work Instructions, PART 4. (a) (b) (d) No crack found.

- - Before further flight. Repair the tension tie aftchannel as given in paragraph 3.B., Work Instructions, PART 4. (c) Crack found.

- Within 2,000flight cycles after the Revision 2 date of this service bulletin.Before the accumulation of 16,000 total flight cycles.Unless previously accomplished, do the tension tie modification as given inParagraph 3.B., Work Instructions, PART 5. All airplanes.

(a) Doing a repair or modification as given in this service bulletin terminates the initial and/or repetitive inspection requirements given in this compliance table. (b) For Group 1 and 2 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 780 to 940. For Group 3 and 7 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 800 to 940. For Group 5 and 6 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 840 to 940. For Group 4 airplanes, do inspections of any unmodified or unrepaired tension ties from STA 820 to 940. (c) Do repeat inspections at locations where no crack was found. Refer to Table 2 for inspection requirements after repair or modification has been done. (d) Additional tension tie inspection requirements are given in Service Bulletin 747-53A2502. **F. Approval** This service bulletin was examined by the Federal Aviation Administration (FAA). The changes specified in this service bulletin comply with the applicable regulations and are FAA approved, as well as European Aviation Safety Agency (EASA)/Joint Aviation Authorities (JAA) approved for all EASA/JAA approved airplanes listed in the service bulletin effectivity. This service bulletin and its approval were based on the airplane in its original Boeing delivery configuration or as modified by other approved Boeing changes.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 19 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**If an airplane has a non-Boeing modification or repair that affects a component or system also affected by this service bulletin, the operator is responsible for obtaining appropriate regulatory agency approval before incorporating this service bulletin. In addition, the Manager of the FAA Seattle Aircraft Certification Office (ACO) approves the accomplishment of the inspection, repair, and modification procedures with corresponding compliance times specified in Service Bulletin 747-53A2371, Revision 2, as an alternative method of compliance to the inspection, repair, and optional modification procedures with corresponding compliance times required by paragraphs (a) and (b) of AD 94-13-06. All provisions of AD 94-13-06 that are not specifically referenced in this paragraph remain fully applicable and must be complied with accordingly. **G. Manpower** The table below shows an estimate of the task hours necessary to do the inspection, repair, or modification for each airplane. This estimate is for direct labor only, done by an experienced crew. Adjust the estimate with operator task hour data if necessary. The estimate does not include lost time. These are some examples of lost time: • Time to adjust to the workplace • Time to schedule the work • Time to inspect the work • Time to cure the materials • Time to make the parts • Time to find the tools. **Table 1: Group 1 and 2 airplanes Elapsed Hours**  **Task Hours Number of Persons**  **Task** 1.0 2.0 2 Open Access 1.5 1.5 1 Inspect 27.0 108.0 4 Repair or Modify 1.0 2.0 2 Close Access TOTAL FOR EACH AIRPLANE 3.5 5.5 INSPECTION ONLY 30.5 113.5 INSPECTION AND REPAIR OR MODIFICA- TION **Table 2: Group 3 and 7 airplanes Elapsed Hours**  **Task Hours Number of Persons**  **Task** 1.0 2.0 2 Open Access 1.25 1.25 1 Inspect 24.0 96.0 4 Repair or Modify 1.0 2.0 2 Close Access TOTAL FOR EACH AIRPLANE

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 20 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Table 2: Group 3 and 7 airplanes**  **Elapsed Hours Task Hours**  **Number of Persons Task**  3.25 5.25 INSPECTION ONLY 27.25 101.25 INSPECTION AND REPAIR OR MODIFICA- TION **Table 3: Group 4 airplanes Elapsed Hours**  **Task Hours Number of Persons**  **Task** 1.0 2.0 2 Open Access 1.0 1.0 1 Inspect 21.0 84.0 4 Repair or Modify 1.0 2.0 2 Close Access TOTAL FOR EACH AIRPLANE 3.0 5.0 INSPECTION ONLY 24.0 89.0 INSPECTION AND REPAIR OR MODIFICA- TION **Table 4: Group 5 and 6 airplanes Elapsed Hours**  **Task Hours Number of Persons**  **Task** 1.0 2.0 2 Open Access 1.0 1.0 1 Inspect 18.0 72.0 4 Repair or Modify 1.0 2.0 2 Close Access TOTAL FOR EACH AIRPLANE 3.0 5.0 INSPECTION ONLY 21.0 77.0 INSPECTION AND REPAIR OR MODIFICA- TION **H. Weight and Balance Changes Group 1 and 2:**  **Change in Moment (Pound-Inches)**  **Change in Weight (Pounds)**  **Airplane** +2,322.0 (a) +2.7 (a) Repair or Modifica- tion (a) The weight and balance data is only for airplanes repaired or modified at all affected locations.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 21 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT Group 3 and 7:**  **Change in Moment (Pound-Inches)**  **Change in Weight (Pounds)**  **Airplane** +2,088.0 (a) +2.4 (a) Repair or Modifica- tion (a) The weight and balance data is only for airplanes repaired or modified at all affected locations. **Group 4: Change in Moment**  **(Pound-Inches) Change in Weight**  **(Pounds) Airplane**  +1,848.0 (a) +2.1 (a) Repair or Modifica- tion (a) The weight and balance data is only for airplanes repaired or modified at all affected locations. **Group 5 and 6: Change in Moment**  **(Pound-Inches) Change in Weight**  **(Pounds) Airplane**  +1,602.0 (a) +1.8 (a) Repair or Modifica- tion (a) The weight and balance data is only for airplanes repaired or modified at all affected locations.
**I. Electrical Load Data** Not changed. **J. References** 1. Existing Data: a. Engineering Change Memo PRR 85901-120RS b. Boeing Service Bulletin 747-25-2692, 747-53-2088, 747-53-2371 c. Boeing Service Letter 747-SL-53-088 d. Boeing Service Related Problem (SRP) 747-SRP-53-0403 e. Federal Aviation Administration (FAA) Airworthiness Directive (AD) 94-13-06 f. Service Bulletin Index D6-30300 g. 747 Non-Destructive Testing (NDT) Manual Part 6, 51-00-00

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 22 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**h. 747-100/200/300 Aircraft Maintenance Manual (AMM) 25-22-01 i. Supplemental Structural Inspection Document (SSID), Boeing Document D6-35022. 2. Data Supplied with this Service Bulletin: None. 3. Installation Drawings Used in the Preparation of this Service Bulletin:
**Title Drawing Number**  Tension Tie Installation - STA 760 to STA 940, STA 1040 to STA 1220 65B09631 Structures Instl - Condor (DF) (Modification Dwg) 65B23200 Structures Instl - Upper Deck Galley and Cart Lift, Mod Dwg (BA) 65B24437 Structures Instl - KLM Mod. Dwg. 65B24474 Tension Tie Installation STA 760 - STA 940 - Mod Dwg 65B24488 Tension Tie - STA 780 to STA 940, Aft Channel, Repair 691U0105 The table above lists applicable drawings used to prepare this service bulletin. The drawings are not necessary to make the specified changes, and are not supplied with this service bulletin. The drawings may not be applicable to all airplane configurations or operators. **K. Publications Affected** 1. Publications: None. 2. Damage Tolerance Based Structural Inspections: Boeing has evaluated the repairs and/or changes in this service bulletin for effects on Fatigue Critical Structure (FCS) and for changes to Damage Tolerance Inspections (DTI) required in the Maintenance Program. This service bulletin affects FCS. DTI requirements for the structure affected are contained in Paragraph 1.E., Compliance of this service bulletin. **L. Interchangeability and Intermixability of Parts** Accomplishment of this service bulletin does not affect interchangeability or intermixability of parts. **M. Software Accomplishment Summary** Not affected.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 23 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 24 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**

BLANK PAGE**2. MATERIAL INFORMATION A. Material - Price and Availability**  None. **B. Industry Support Information** This service bulletin was first released before October of 1994. Thus industry support for affected airplanes depends upon whether you ever filed a warranty claim with Boeing on this service bulletin. **C. Parts Necessary for Each Airplane** 1. Kits/Parts None. 2. Parts and Materials Supplied by the Operator The following parts or materials are necessary to do the change in this service bulletin. Parts and materials in the manuals shown in Paragraph 1.J., References, can also be necessary. Examine operator part and material supply to make sure all necessary parts and materials are available.

- - Airplane Group

- - 1 2 3 4 5 6 7 Name Part Number Quantity Strap A (a) 2 2

. . . . . Strap B (a) 2 2 2

. . . . Strap C (a) 2 2 2 2

. . 2 Strap D (a) 2 2 2 2 2 2 2 Strap E (a) 2 2 2 2 2 2 2 Strap F (a) 2 2 2 2 2 2 2 Strap G (a) 2 2 2 2 2 2 2 Strap H (a) 2 2 2 2 2 2 2 Strap I (a) 2

. . 2 2

. 2 Strap J (a)

. 2 2

. . 2

. Bolt BACB30MY6K3X 20 20 20 12 10 10 20 Bolt BACB30MY6K4X 88 88 80 70 58 58 80 Bolt BACB30MY6K4Y 72 72 64 56 48 48 64 Bolt BACB30MY6K5X 66 68 62 60 58 60 60 Bolt BACB30MY6K6X 64 60 60 64 46 42 64 Bolt BACB30MY6K7X 54 60 60 38 38 44 54

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 25 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Bolt BACB30MY6K8X 28 28 18 18 18 18 18 Bolt BACB30MY6K9X 10 10

. . . . . Bolt BACB30MY8K4 36 36 32 28 24 24 32 Collar BACC30M6 298 302 272 238 206 210 268 Collar BACC30M8 36 36 32 28 24 24 32 Collar BACC30R6 72 72 64 56 48 48 64 Sealant BMS 5-95 (b) 1 quart 1 quart 1 quart 1 quart 1 quart 1 quart 1 quart (a) Make as given in FIGURE 7. (b) Refer to the Qualified Products List at the end of the Boeing Material Specification (BMS) for supplier data.
3. Parts Modified and Reidentified None. 4. Parts Removed and Not Replaced None. **D. Parts Necessary to Change Spares** None. **E. Special Tooling - Price and Availability** None. **F. Special Tooling Necessary to do this Service Bulletin** No special tools or equipment are necessary to do the change in this service bulletin. But, maintenance and overhaul tools in the manuals shown in Paragraph 1.J., References, can be necessary. Examine operator tool supply to make sure all necessary tools are available.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 26 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT 3. ACCOMPLISHMENT INSTRUCTIONS**  **A. GENERAL INFORMATION CAUTION:**  KEEP THE WORK AREA, WIRES AND ELECTRICAL BUNDLES CLEAN OF METAL PARTICLES OR CONTAMINATION WHEN YOU USE TOOLS. UNWANTED MATERIAL, METAL PARTICLES OR CONTAMINATION CAUGHT IN WIRE BUNDLES CAN CAUSE DAMAGE TO THE BUNDLES. DAMAGED WIRE BUNDLES CAN CAUSE SPARKS OR OTHER ELECTRICAL DAMAGE. **NOTE:** 1. Manual titles are referred to by acronyms. Refer to Paragraph 1.J., References, for definition of the acronyms. 2. Obey all of the warnings and cautions given in the specified manual sections. 3. Unless shown differently, these dimensions and tolerances are used: – Linear dimensions are in inches – Tolerance on linear dimensions, other than rivet and bolt edge margins, is plus or minus 0.03 inch – Tolerance on rivet and bolt edge margin is plus or minus 0.05 inch – Angular tolerance is plus or minus 2 degrees – Hole dimensions for standard solid rivets and fasteners are in Structural Repair Manual (SRM) Chapter 51 – Torque limits to tighten nuts and bolts are in SRM Chapter 51 4. Use the approved fastener and process material substitutions as given in SRM Chapter 51. 5. If the length of any fastener specified in this service bulletin does not meet installation standards given in SRM Chapter 51, then a fastener of the same specification, or an approved substitute, with a length which meets the installation standards given in SRM Chapter 51 may be used. In addition, washers may be installed for fastener grip length as given in SRM Chapter 51. 6. There is no economics based inspection program for the area affected by this service bulletin. The repair necessary when a crack is found in the flight safety inspection is the same as the repair necessary if a crack is found earlier. 7. Report any STA 780 - 940 tension tie damage. Use the reporting system described in Appendix A of this service bulletin. 8. A Detailed Inspection is defined as: An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirrors, magnifying lenses, etc. may be necessary. Surface cleaning and elaborate procedures may be required. 9. Boeing Service Letter 747-SL-51-048, Damage Reporting and Repair Plan/Design Guidelines, is an acceptable procedure to request information from Boeing for additional structural repair instructions. The Service Letter describes what information must be provided to Boeing before a structural repair can be provided.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 27 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**10. The instructions in Paragraph 3.B., Work Instructions and the figures can include operation of tools or test equipment. Boeing Engineering Tool Drawings, the Illustrated Tool and Equipment Manual, and the Special Tool and Ground Handling Drawing Index contain data on versions of the tools or test equipment that you can use. It is permitted to use replaced tools. It is not permitted to use superseded tools. 11. If it is necessary to remove more parts for access, you can remove those parts. If you can get access without removing identified parts, it is not necessary to remove all of the identified parts. Jacking and shoring limitations must be observed. 12. Where the work instructions include installation of a kept part, a new or serviceable part with the same part number can be installed as an alternative to the kept part. 13. These work instructions refer to procedures included in other Boeing documents. When the words "refer to" are used and the operator has an accepted alternative procedure, the accepted alternative procedure can be used. When the words "as given in" are included in the instruction, the procedure in the Boeing document must be used. **B. WORK INSTRUCTIONS** NOTE: When possible, Boeing recommends accomplishment of PART 4 inspection to be done concurrently with PART 1 inspection. **PART 1 - TENSION TIE DETAILED INSPECTION** 1. Remove the ceiling access panels in the main passenger cabin from STA 780 to 940. Refer to 747-100/200/300 AMM 25-22-01. 2. Do a detailed inspection for cracks in the tension ties as given in FIGURE 2. The table that follows shows the affected tension tie locations.
Tension Ties Affected Airplane Group STA 940 STA 920 STA 900 STA 880 STA 860 STA 840 STA 820 STA 800 STA 780 X X X X X X X X X Groups 1 and 2 X X X X X X X X

- Groups 3 and 7 X X X X X X X

- - Group 4 X X X X X X

- - - Groups 5 and 6
**NOTE:** An X shows that inspection of the tension tie at that location is necessary. 3. If no cracks are found, continue to PART 3. Do the inspection given in FIGURE 2 again at the time given in Paragraph 1.E., Compliance. **NOTE:** As an alternative, modify all affected tension ties as given in FIGURE 3. Do inspections of the modified tension ties as given in PART 2.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 28 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**4. If cracks are found in the aft channel, repair as given in FIGURE 3 before any more flights. If cracks are found at other locations, repair before any more flights. Contact Boeing for repair instructions. Do inspections of the repaired tension ties as given in PART 2. **NOTE:** – Continue to do inspections of affected tension ties that have not been repaired or modified. Do the inspection given in FIGURE 2 again at the time given in Paragraph 1.E., Compliance . – If the repair given in FIGURE 3 does not completely remove cracks in the aft channel, contact Boeing for repair instructions and do the repair. 5. Continue to PART 3. **PART 2 - AFTER MODIFICATION INSPECTION PROGRAM** 1. Remove the ceiling access panels in the main passenger cabin from STA 780 to 940. Refer to 747-100/200/300 AMM 25-22-01. 2. Do inspections of the repaired or modified tension ties as given in FIGURE 6. The table that follows shows the affected tension tie locations.
Tension Ties Affected Airplane Group STA 940 STA 920 STA 900 STA 880 STA 860 STA 840 STA 820 STA 800 STA 780 X X X X X X X X X Groups 1 and 2 X X X X X X X X

- Groups 3 and 7 X X X X X X X

- - Group 4 X X X X X X

- - - Groups 5 and 6
**NOTE:** An X shows that inspection of the tension tie at that location is necessary. 3. If no cracks are found, continue to PART 3. Do the inspection given in FIGURE 6 again at the time given in Paragraph 1.E., Compliance . 4. If cracks are found, contact Boeing for repair instructions and do the repair. 5. Continue to PART 3. **PART 3 - RESTORATION** 1. Install the ceiling access panels in the main passenger cabin from STA 780 to STA 940. Refer to 747-100/200/300 AMM 25-22-01. 2. Put the airplane back to a serviceable condition. **PART 4 - TENSION TIE HIGH FREQUENCY EDDY CURRENT INSPECTION** 1. Remove the ceiling access panels in the main passenger cabin from STA 780 to 940. Refer to 747-100/200/300 AMM 25-22-01.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 29 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**2. Do a surface high frequency eddy current (HFEC) inspection for cracks in the tension ties as given in FIGURE 8. The table that follows shows the affected tension tie locations.
Tension Ties Affected Airplane Group STA 940 STA 920 STA 900 STA 880 STA 860 STA 840 STA 820 STA 800 STA 780 X X X X X X X X X Groups 1 and 2 X X X X X X X X

- Groups 3 and 7 X X X X X X X

- - Group 4 X X X X X X

- - - Groups 5 and 6
**NOTE:** An X shows that inspection of the tension tie at that location is necessary. 3. If no cracks are found, continue to PART 3. Do the inspection given in FIGURE 8 again at the time given in Paragraph 1.E., Compliance. **NOTE:** As an alternative, modify all affected tension ties as given in FIGURE 3. Do inspections of the modified tension ties as given in PART 2. 4. If cracks are found in the aft channel, repair as given in FIGURE 3 before any more flights. Do inspections of the repaired tension ties as given in PART 2, at the times given in Paragraph 1.E., Compliance. **NOTE:** – Continue to do inspections of affected tension ties that have not been repaired or modified. Do the inspection given in FIGURE 8 again at the time given in Paragraph 1.E., Compliance. – If the repair given in FIGURE 3 does not completely remove cracks in the aft channel, contact Boeing for repair instructions and do the repair. 5. Continue to PART 3. **PART 5 - MODIFICATION (More Work)** 1. Remove the ceiling access panels in the main passenger cabin from STA 780 to 940. Refer to 747-100/200/300 AMM 25-22-01. 2. For any tension tie locations that have not previously been repaired or modified as given in this service bulletin, do the modification as given in FIGURE 3. 3. Do inspections of the modified tension ties as given in PART 2 - AFTER MODIFICATION INSPECTION PROGRAM, at the times given in Paragraph 1.E., Compliance. 4. Restore the airplane as given in PART 3 - RESTORATION.

Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2: December 11, 2012 30 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 1: THIS FIGURE IS DELETED (REVISION 2)**  **(SHEET 1 OF 1)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 31 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 2: TENSION TIE DETAILED INSPECTION**  **(SHEET 1 OF 2)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 32 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**The step numbers shown below agree with the numbers shown in the circle symbols in the figure.
**More Data Qty**  **Identification Name**  **Task Step**  (a)

- - Tension Tie Inspect 1 (a) Do a detailed inspection for cracks in the outboard 30 inches of the tension tie. Do the inspection at both ends of the tension tie.

**FIGURE 2: TENSION TIE DETAILED INSPECTION (SHEET 2 OF 2)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 33 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 1 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 34 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 2 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 35 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 3 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 36 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 4 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 37 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 5 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 38 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 6 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 39 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 7 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 40 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 8 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 41 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 9 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 42 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 10 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 43 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 11 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 44 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 3: REPAIR OR MODIFICATION**  **(SHEET 12 OF 14)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 45 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**The step numbers shown below agree with the numbers shown in the circle symbols in the figure. The QTY numbers shown below are the number of parts necessary for one tension tie on one side of the airplane. **NOTE:** The figure shows two alternate aft channel trims. Any trim line that is between those shown in the figure is acceptable. At least five fasteners in each row are necessary inboard of the trim line.
**More Data Qty**  **Identification Name**  **Task Step**  (a) 21 - 28

- Fasteners Remove 1

- 1

- Plate Remove / Keep 2

- 1

- Aft Channel Trim 3

- 1

- Trimmed Section Remove 4 to match adjacent structure. 1

- Aft Channel Paint 5 at STA 780. 1 A Repair Strap Install (b) (c)

6 at STA 800. 1 B Repair Strap at STA 820. 1 C Repair Strap at STA 840. 1 D Repair Strap at STA 860. 1 E Repair Strap at STA 880. 1 F Repair Strap at STA 900. 1 G Repair Strap at STA 920. 1 H Repair Strap at STA 940 for Groups 1, 4, 5, and 7. 1 I Repair Strap

at STA 940 for Groups 2, 3, and 6. 1 J Repair Strap

1

- Plate (Kept) Install (b) 7 (a) Number of fasteners removed depends on trim line and tension tie location. (b) Install with BMS 5-95 sealant. (c) Trim the repair strap as necessary for installation.

**FIGURE 3: REPAIR OR MODIFICATION (SHEET 13 OF 14)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 46 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**The codes shown below agree with the letter shown in the upper left corner of the fastener symbols in the figure. A number in the lower right corner gives the grip length of the fastener. The QTY numbers shown below are the number of fasteners necessary for this figure. If the grip length shown is not available at Boeing, fasteners supplied in kits may be one grip length longer than indicated. Also, if any of the fastener part numbers are not available or have been superseded, substitute fasteners may be supplied in Boeing kits.
**NOTES HOLE DIA**  **PART NUMBER NAME**  **CODE** Install with BMS 5-95 sealant. 0.2026 - 0.2036 BACB30MY6K( )X Bolt A BACC30M6 Collar Install with BMS 5-95 sealant. 0.216 - 0.219 BACB30MY6K4Y Bolt B BACC30R6 Collar Install with BMS 5-95 sealant. 0.2495 - 0.2505 (a) BACB30MY8K4 Bolt C BACC30M8 Collar (a) Before the hole is made larger, do open hole HFEC inspections at these locations. Use 747 NDT Manual Part 6, 51-00-00, Procedure 1, 11, or 16. If no cracks are found, make the fastener holes the size given in the table.

**FIGURE 3: REPAIR OR MODIFICATION (SHEET 14 OF 14)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 47 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 4: THIS FIGURE IS DELETED (REVISION 2)**  **(SHEET 1 OF 1)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 48 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 5: THIS FIGURE IS DELETED (REVISION 2)**  **(SHEET 1 OF 1)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 49 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 6: AFTER MODIFICATION INSPECTION**  **(SHEET 1 OF 2)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 50 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**The step numbers shown below agree with the numbers shown in the circle symbols in the figure.
**More Data Qty**  **Identification Name**  **Task Step**  (a)

- - Tension Tie Inspect 1 (a) Do a detailed inspection for cracks in the outboard 30 inches of the tension tie. Do the inspection at both ends of the tension tie.

**FIGURE 6: AFTER MODIFICATION INSPECTION (SHEET 2 OF 2)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 51 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Dimension Repair Strap Z Y X W 10.6 9.8 11.8 1.4 A 10.6 11.5 12.2 1.0 B 10.6 11.1 12.1 1.1 C 10.0 11.7 13.1 1.3 F 13.3 12.5 14.6 1.7 H 13.6 12.4 14.1 1.3 I 14.3 13.1 14.4 1.4 J

**FIGURE 7: REPAIR STRAP FABRICATION (SHEET 1 OF 3)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 52 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Dimension Repair Strap Y X 12.8 11.1 D 13.5 11.6 E 14.3 12.0 G

**FIGURE 7: REPAIR STRAP FABRICATION (SHEET 2 OF 3)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 53 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**The step numbers shown below agree with the numbers shown in the circle symbols in the figure. The QTY numbers shown below are the number of parts necessary for the airplane..
**MORE DATA QTY**  **PART NUMBER NAME**  **TASK STEP**  0.071 thick 2024-T3 2 A Repair Strap Make 1 2 B 2 C 2 F 2 H 2 I 2 J 0.071 thick 2024-T3 2 D Repair Strap Make 2 2 E 2 G One coat BMS 10-11, Type I

- - Repair Strap Paint 3

**FIGURE 7: REPAIR STRAP FABRICATION (SHEET 3 OF 3)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 54 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 8: TENSION TIE HIGH FREQUENCY EDDY CURRENT INSPECTION**  **(SHEET 1 OF 3)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 55 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT FIGURE 8: TENSION TIE HIGH FREQUENCY EDDY CURRENT INSPECTION**  **(SHEET 2 OF 3)**
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 56 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**The step numbers shown below agree with the numbers shown in the circle symbols in the figure.
**More Data Qty**  **Identification Name**  **Task Step**  (a)

- - Tension Tie Inspect 1 (a) Do a surface high frequency eddy current (HFEC) inspection for cracks on the edge of the radius of the tension tie aft channel at the two locations shown. Do the inspection at both ends of the tension tie. Refer to 747 NDT Manual Part 6, 51-00-00, Procedure 4 or 23, as an accepted procedure.

**FIGURE 8: TENSION TIE HIGH FREQUENCY EDDY CURRENT INSPECTION (SHEET 3 OF 3)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 57 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**APPENDIX A: INSPECTION TO ENSURE STRUCTURAL INTEGRITY OF AIRFRAME A structural reassessment of the 747 airplane has been conducted under the requirements of Federal Aviation Administration (FAA) Advisory Circular 91-56, in accordance with Federal Aviation Regulation (FAR) 25.571 as amended in 1978, to ensure safe operation of 747 airplanes throughout their operational life. Table 1 is a summary of the inspection and modification actions specified in Paragraph 3.B., Work Instructions. These inspection and modification actions are recommended for the detection and prevention of cracks in the upper deck tension ties from STA 780 to 940. The failure of more than one tension tie can result in rapid depressurization of the airplane. Any cracks in the forward channel of an upper deck tension tie should be repaired before any more flights. Do this unless specifically approved by your cognizant regulatory agency. Please report any discrepancies using the reporting system described in this addendum. **TABLE 1: SUMMARY OF FLIGHT SAFETY INSPECTION PROGRAM Repeat Inspection Inter**  **val Inspection Threshold**  **Inspection Method Airplane Condition**  3,000 flight cycles. Before the accumulation of 1,000 flight cycles after July 27, 1994. Detailed Inspection Service Bulletin 747-53A2371 Repair or Modification Not Installed 3,000 flight cycles. Concurrent with the nextplanned detailed inspection. Surface High FrequencyEddy Current (HFEC) Inspection (a) 6,000 flight cycles. Within 10,000 flight cycles after Repair or Modification Detailed Inspection Service Bulletin 747-53A2371 Repair or Modification Installed (a) For airplanes that cannot incorporate the surface HFEC inspection at the next planned detailed inspection, do the first surface HFEC inspection within 3,000 flight cycles after the Revision 2 date of this service bulletin. Boeing requests that operators use the following Structural Significant Item (SSI) Reporting System to report any discrepancies that are found during accomplishment of a Flight Safety Inspection. 1. Upon recognition of a discrepancy, the following information should be sent to Boeing: Heading: ATTENTION - SSI DISCREPANCY - SERVICE BULLETIN RELATED – Service Bulletin Number – Airplane serial number upon which discrepancy was found – Identification of structural item found damaged – Flight-cycles and hours on damaged item – Location and description of damage including direction and size – When discovered and inspection method used.

**APPENDIX A: FLIGHT SAFETY SECTION (SHEET 1 OF 2)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 58 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**Send the report through Boeing Field Service Representative or directly to: 747 Airline Support 2. An Operator's Follow-up Report containing all available pertinent data relative to the structural discrepancy shall be sent to Boeing. A summary of the information that should be reported is shown in the SSI DISCREPANCY REPORT form in the Supplemental Structural Inspection Document (SSID), Boeing Document D6-35022. Operators may use this form or any suitable alternative which contains the same information. 3. All data and reports dealing with the Flight Safety Inspection Program shall be submitted either through a Boeing Field Service Representative or directly to: Boeing Commercial Airplane Group P.O. Box 3707 Seattle, Washington 98124 Attn: Manager, Airline Support 4. All reports will be reviewed immediately. 5. The Boeing Company will summarize the results of all reported significant data for distribution semiannually to operators and appropriate Airworthiness Authorities.

**APPENDIX A: FLIGHT SAFETY SECTION (SHEET 2 OF 2)** 
Export Controlled ECCN: 9E991 - BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: July 29, 1993 747-53A2371 Revision 2 December 11, 2012 59 of 59 **BOEING SERVICE BULLETIN 747-53A2371 ALERT**  **ALERT**