### Commercial **Airplanes** 

# 737 Service Bulletin **ALERT Number: 737-53A1319**  Original Issue: April 04, 2011 ATA System: 5331 **SUBJECT:** FUSELAGE - Skin - Crown Skin Lap Joint - Inspection for Lower Row Cracking at Stringer S-4, Between BS 360 and BS 908 Export of this technology is controlled under the United States Export Administration Regulations (EAR) (15 CFR 730-774). 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## BOEING PROPRIETARY, CONFIDENTIAL, AND/OR TRADE SECRET Copyright © 2011 The Boeing Company Unpublished Work - All Rights Reserved Boeing claims copyright in each page of this document only to the extent that the page contains copyrightable subject matter. Boeing also claims copyright in this document as a compilation and/or collective work. This document includes proprietary information owned by The Boeing Company and/or one or more third parties. Treatment of the document and the information it contains is governed by contract with Boeing. For more information, contact The Boeing Company, P.O. Box 3707, Seattle, Washington 98124. 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, KDC-10, MD-10, MD-11, MD-80, MD-88, MD-90, P-8A, Poseidon and the Boeing livery 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BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 1 of 33 2.0BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 2 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**

BLANK PAGE**Table of Contents** Summary...................................................... 5 1. PLANNING INFORMATION ........................................ 9 A. Effectivity................................................ 9 1. Airplanes............................................. 9 2. Spares Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 B. Concurrent Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 C. Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 D. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 E. Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 F. Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 G. Manpower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 H. Weight and Balance Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 I. Electrical Load Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 J. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1. Existing Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2. Data supplied with this Service Bulletin. . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3. Installation Drawings Used in the Preparation of this Service Bulletin. . . . . . . . . . . . 14 K. Publications Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 L. Interchangeability and Intermixability of Parts. . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2. MATERIAL INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 A. Material - Price and Availability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 B. Industry Support Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 C. Parts Necessary For Each Airplane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1. Kits/Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2. Parts and Materials Supplied by the Operator. . . . . . . . . . . . . . . . . . . . . . . . 17 3. Parts Modified and Reidentified. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4. Parts Removed and Not Replaced. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 D. Parts Necessary to Change Spares. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 E. Special Tooling - Price and Availability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 F. Special Tooling Necessary to do this Service Bulletin. . . . . . . . . . . . . . . . . . . . . . . 17 3. ACCOMPLISHMENT INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 A. GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 B. WORK INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 FIGURE 1: EXTERNAL INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 FIGURE 2: ALTERNATIVE INTERNAL INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . 23 FIGURE 3: CONFIRMING A CRACK INDICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 FIGURE 4: SECOND EXTERNAL INSPECTION - INSPECTION LOCATION. . . . . . . . . . . . . . 29 FIGURE 5: INSPECTION ZONES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 3 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 4 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**

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### Commercial **Airplanes** 

# 737 Service Bulletin **ALERT Summary**  **Number: 737-53A1319** Original Issue: April 04, 2011 ATA System: 5331 **SUBJECT:** FUSELAGE - Skin - Crown Skin Lap Joint - Inspection for Lower Row Cracking at Stringer S-4, Between BS 360 and BS 908 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** Recently, a 737-300 airplane, outside of the effectivity of Service Bulletin (SB) 737-53A1255, experienced a rapid decompression when the lap joint at stringer S-4L between BS 664 - BS 727 cracked and opened up. Investigation shows that the cracking was caused by fatigue cracking in the lower skin at the lower row of fasteners in the lap joint. The airplane had 39,781 total flight cycles and 48,740 total flight hours. This service bulletin gives instructions to inspect the lower row of fasteners at stringer S-4R and S-4L, from BS 360 to BS 908 for cracking in the lower skin of the lap joint. If cracking at this location goes undetected, the cracks could link up, resulting in an uncontrolled decompression. Airplanes prior to Line Number 2553 are covered by Service Bulletin (SB) 737-53A1255. This SB covers airplanes from Line Number 2553 to 3132. **ACTION** Do a Non Destructive Test (NDT) Dual Frequency Eddy Current (DFEC) external inspection of the lap joint at stringers S-4R and S-4L along the entire length from BS 360 to BS 908. As an option to doing the external DFEC inspection of the lap joint, you can get access to the interior fuselage and do NDT eddy current and Detailed Inspections. As an option, crack indications can be confirmed by doing internal eddy current inspections. If a crack is found, contact Boeing for a repair and do the repair. **EFFECTIVITY** 737-300, 737-400, and 737-500 Airplanes. Refer to Paragraph 1.A.1., Airplanes, for the list of affected airplanes.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 5 of 33**COMPLIANCE** 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** At the time of release of this service bulletin, warranty remedies have not been determined. A subsequent revision or Information Notice will address the warranty remedies available, if any. **MANPOWER** TBD **MATERIAL INFORMATION** None.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 6 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 7 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 8 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**

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### Commercial **Airplanes** 

# 737 Service Bulletin **ALERT Number: 737-53A1319**  Original Issue: April 04, 2011 ATA System: 5331 **SUBJECT:** FUSELAGE - Skin - Crown Skin Lap Joint - Inspection for Lower Row Cracking at Stringer S-4, Between BS 360 and BS 908 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

**DESCRIPTION CONFIGURATION**  **GROUP** 737-300, 737-400 and 737-500 Airplanes

- 1

Airplane Models: 737-300, 737-400, 737-500 **Group Variable Number**  1 PJ552 - PJ561 1 PJ601 - PJ615 1 PJ811 1 PJ816 - PJ817 1 PM543 - PM550 1 PP518 - PP520 1 PP876 - PP877 1 PQ297 - PQ299 1 PQ345 - PQ348

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 9 of 33**Group Variable Number**  1 PQ370 - PQ373 1 PQ391 - PQ395 1 PQ408 - PQ410 1 PQ414 - PQ418 1 PQ431 - PQ438 1 PQ447 - PQ448 1 PQ451 1 PQ454 1 PQ473 - PQ475 1 PQ772 1 PQ933 - PQ935 1 PQ951 1 PQ971 - PQ997 1 PR001 - PR017 1 PR021 - PR034 1 PR041 - PR045 1 PR061 - PR072 1 PR077 - PR082 1 PR091 - PR092 1 PR096 1 PR101 1 PR121 - PR122 1 PR131 - PR132 1 PR141 - PR143 1 PR161 - PR172 1 PR181 1 PS617 - PS630 1 PS704 - PS706 1 PS763 - PS799 1 PS811 1 PS836 - PS837 1 PS841 - PS846 1 PS851 - PS852

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 10 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT Group**  **Variable Number** 1 PS856 1 PS861 - PS863 1 PS866 - PS868 1 PS871 - PS874 1 PS896 - PS897 1 PS901 - PS941 1 PS956 - PS957 1 PS961 - PS963 1 PS971 - PS978 1 PT012 - PT015 1 PT029 - PT031 1 PT064 1 PT126 - PT138 1 PT188 1 PT307 - PT309 1 PT513 - PT517 1 PT585 - PT586 1 PT643 - PT644 1 PT656 1 PT681 - PT685 1 PT716 - PT717 1 PT721 - PT725 1 PT801 - PT834 1 PT851 - PT854 1 PT871 - PT886 1 PT901 - PT930 1 PT971 - PT973 1 PT981 - PT985 1 PT996 1 PU301 1 PU311 - PU313 1 PV204 - PV209 1 PV226 - PV229

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 11 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT Group**  **Variable Number** 1 PV284 - PV287 1 PV296 1 PV301 - PV302 1 PV351 1 PV356 - PV357 1 PW086 - PW088 1 PW168 - PW171 1 PW245 - PW252 1 PW262 - PW264 1 PW271 - PW276 1 PW282 - PW292 1 PW401 - PW408 1 PW411 - PW418 1 PW421 - PW424 1 PW431 - PW435 1 PW441 - PW450 1 PW521 - PW522 1 PW524 - PW525 1 PW527 - PW530 1 PW547 - PW550 1 PW621 - PW622 1 PW635 - PW637 1 PW831 1 PW851 - PW856 2. Spares Affected
**B. Concurrent Requirements** None.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 12 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT C. Reason**  Recently, a 737-300 airplane, outside of the effectivity of Service Bulletin (SB) 737-53A1255, experienced a rapid decompression when the lap joint at stringer S-4L between BS 664 - BS 727 cracked and opened up. Investigation shows that the cracking was caused by fatigue cracking in the lower skin at the lower row of fasteners in the lap joint. The airplane had 39,781 total flight cycles and 48,740 total flight hours. This service bulletin gives instructions to inspect the lower row of fasteners at stringer S-4R and S-4L, from BS 360 to BS 908 for cracking in the lower skin of the lap joint. If cracking at this location goes undetected, the cracks could link up, resulting in an uncontrolled decompression. Airplanes prior to Line Number 2553 are covered by Service Bulletin (SB) 737-53A1255. This SB covers airplanes from Line Number 2553 to 3132. **D. Description** Do a Non Destructive Test (NDT) Dual Frequency Eddy Current (DFEC) external inspection of the lap joint at stringers S-4R and S-4L along the entire length from BS 360 to BS 908. As an option to doing the external DFEC inspection of the lap joint, you can get access to the interior fuselage and do NDT eddy current and Detailed Inspections. As an option, crack indications can be confirmed by doing internal eddy current inspections. If a crack is found, contact Boeing for a repair and do the repair. The work in this service bulletin is done in the maintenance zone(s) given below.
**Affected Maintenance Zones Zone**  **Model** 107, 108 737-300, 737-400, 737-500 **E. Compliance** 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. Boeing recommends that the inspections be done before the airplane has 30,000 total flight cycles or within 20 days of the original issue date of this SB, whichever occurs later. For airplanes with 30,000 to 34,999 total flight cycles, do the inspections within 20 days of the original issue date of this SB. For airplanes that have 35,000 total flight cycles or more, do the inspections within 5 days of the original issue date of this SB. Repeat the inspections at intervals not to exceed 500 flight cycles. If a crack is found, contact Boeing for a repair and do the repair.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 13 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT 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. 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. **G. Manpower** TBD **H. Weight and Balance Changes** None. **I. Electrical Load Data** None. **J. References** 1. Existing Data a. Boeing Service Bulletin 737-53A1255 b. 737 NDT Part 6, 51-00-00 Figure 16, 53-30-00 Figure 9, 53-30-12, 53-30-16 c. Boeing Service Letter 737-SL-51-042 2. Data supplied with this Service Bulletin None. 3. Installation Drawings Used in the Preparation of this Service Bulletin None. **K. Publications Affected** 1. Publications: None. 2. Damage Tolerance Based Structural Inspections:

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 14 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**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 does not affect FCS, therefore DTIs are not necessary.
**L. Interchangeability and Intermixability of Parts** None.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 15 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 16 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**

BLANK PAGE**2. MATERIAL INFORMATION A. Material - Price and Availability**  None. **B. Industry Support Information** At the time of release of this service bulletin, warranty remedies have not been determined. A subsequent revision or Information Notice will address the warranty remedies available, if any. **C. Parts Necessary For Each Airplane** 1. Kits/Parts None. 2. Parts and Materials Supplied by the Operator None. 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 given in Paragraph 1.J., References, can be necessary. Examine operator tool supply to make sure all necessary tools are available.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 17 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 18 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**

BLANK PAGE**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. The instructions identified in Paragraph 3.B., Work Instructions and the Figure(s) give the recommended sequence of steps. The sequence of steps to do this service bulletin can be changed. 2. Manual titles are referred to by acronyms. Refer to Paragraph 1.J., References, for definition of the acronyms. 3. Obey all of the warnings and cautions given in the specified manual sections. 4. 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 5. Use the approved fastener and process material substitutions in accordance with SRM Chapter 51. 6. 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 in accordance with SRM Chapter 51. 7. 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. 8. 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 "in accordance with" are included in the instruction, the procedure in the Boeing document must be used.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 19 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**9. Boeing Service Letter, 737-SL-51-042, 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. 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. **B. WORK INSTRUCTIONS** NOTE: Inspection procedures 737 NDT Part 6, 53-30-16 and 737 NDT Part 6, 53-30-12 show limited effectivity. The inspections applicable to the lap joint lower rows in these procedures are applicable to the full effectivity in this service bulletin. 1. Do external eddy current inspections for cracks in the lower skin at the lap joint lower fastener row at stringer S-4L and S-4R at the locations shown in Figure 5 as follows: a. Do the first inspection for cracks along the centerline in accordance with Figure 1. b. Do a second inspection for cracks along the lower edge of the fastener countersunk heads in accordance with Figure 4. c. It is not required to inspect the lower skin at the lap joint lower fastener row under existing external repair doublers provided: (1) The installed repair was approved by the FAA or by a Boeing Authorized Representative who was authorized by the FAA to make such findings. (2) The installed repair extends a minimum of three rows of fasteners above the chem-mill step and three rows of fasteners below the lap joint lower row. If the repair does not meet the above conditions, then inspect the lower skin lap joint lower row internally in the area covered by the doubler in accordance with Figure 2. 2. As an alternative to doing the external eddy current inspection, you can get access to the interior fuselage and do eddy current inspection and Detailed Inspection for cracks in the lower skin at the lower row of fasteners at stringer S-4L and S-4R in accordance with Figure 2. 3. As an option, crack indications can be confirmed by gaining access to the interior fuselage, as required, and doing an internal eddy current inspection for cracking in the lower skin at the crack indication in accordance with Figure 3. 4. If any crack is found in the lap joint, contact Boeing for a repair and do the repair.

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 20 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 1: EXTERNAL INSPECTION**  **(SHEET 1 OF 2)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 21 of 33 **BOEING SERVICE BULLETIN 737-53A1319 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)

- - Crown Lap Joints Lower Skin Inspect 1 (a) Do an external eddy current inspection for cracking in the lap joint lower fastener row in accordance with 737 NDT Part 6, 53-30-00 Figure 9.

**FIGURE 1: EXTERNAL INSPECTION (SHEET 2 OF 2)** 

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 22 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 2: ALTERNATIVE INTERNAL INSPECTION**  **(SHEET 1 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 23 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 2: ALTERNATIVE INTERNAL INSPECTION**  **(SHEET 2 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 24 of 33 **BOEING SERVICE BULLETIN 737-53A1319 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**  Between tear straps (a)(b)

- - Crown Lap Joints Lower Skin Inspect 1 At tear straps (a)(c)

- - Crown Lap Joints Lower Skin Inspect 2
Where lower skin doubler is not chem-milled at the lap joint (a)(d) - - Crown Lap Joints Lower Skin Inspect 3

(a) Do a Detailed Inspection of the lap joint lower fastener row for cracking. (b) Do an internal Mid Frequency Eddy Current (MFEC) inspection for cracking in the lap joint lower fastener row between tear straps in accordance with 737 NDT Part 6, 53-30-16. (c) Do a Low Frequency Eddy Current (LFEC) inspection for cracking in the lap joint lower fastener row through the tear strap in accordance with 737 NDT Part 6, 53-30-12. (d) Do a Low Frequency Eddy Current (LFEC) inspection for cracking in the lap joint lower fastener row through the lower doubler in accordance with 737 NDT Part 6, 53-30-12.

**FIGURE 2: ALTERNATIVE INTERNAL INSPECTION (SHEET 3 OF 3)** 

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 25 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 3: CONFIRMING A CRACK INDICATION**  **(SHEET 1 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 26 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 3: CONFIRMING A CRACK INDICATION**  **(SHEET 2 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 27 of 33 **BOEING SERVICE BULLETIN 737-53A1319 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**  Between tear straps (a)

- - Crown Lap Joints Lower Skin Inspect 1 At tear straps (b)

- - Crown Lap Joints Lower Skin Inspect 2
Where lower skin doubler is not chem-milled at the lap joint (c) - - Crown Lap Joints Lower Skin Inspect 3

(a) If there was a crack indication at this location as a result of the external eddy current inspection: do an internal Mid Frequency Eddy Current (MFEC) inspection for cracking in the lap joint lower fastener row between tear straps in accordance with 737 NDT Part 6, 53-30-16. (b) If there was a crack indication at this location: do a Low Frequency Eddy Current (LFEC) inspection for cracking in the lap joint lower fastener row through the tear strap in accordance with 737 NDT Part 6, 53- 30-12 or do 737 NDT Part 6, 51-00-00 Figure 16 hole probe inspection. Use 0.03 inch notch standard for the 737 NDT Part 6, 51-00-00, Figure 16 inspection. (c) If there was a crack indication at this location: do a Low Frequency Eddy Current (LFEC) inspection for cracking in the lap joint lower fastener row through the lower doubler in accordance with 737 NDT Part 6, 53-30-12 or do 737 NDT Part 6, 51-00-00 Figure 16 hole probe inspection. Use 0.03 inch notch standard for the 737 NDT Part 6, 51-00-00, Figure 16 inspection.

**FIGURE 3: CONFIRMING A CRACK INDICATION (SHEET 3 OF 3)** 

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 28 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 4: SECOND EXTERNAL INSPECTION - INSPECTION LOCATION**  **(SHEET 1 OF 2)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 29 of 33 **BOEING SERVICE BULLETIN 737-53A1319 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)

- - Crown Lap Joints Lower Skin Inspect 1 (a) Do an external eddy current inspection for cracking in the lap joint lower fastener row in accordance with 737 NDT Part 6, 53-30-00 Figure 9. Move the centerline of the probe along the lower edge of the fastener countersunk heads.

**FIGURE 4: SECOND EXTERNAL INSPECTION - INSPECTION LOCATION (SHEET 2 OF 2)** 

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 30 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 5: INSPECTION ZONES**  **(SHEET 1 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 31 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 5: INSPECTION ZONES**  **(SHEET 2 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 32 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT FIGURE 5: INSPECTION ZONES**  **(SHEET 3 OF 3)**

BOEING PROPRIETARY - Copyright © Unpublished Work - See page 1 for details. Original Issue: April 04, 2011 737-53A1319 33 of 33 **BOEING SERVICE BULLETIN 737-53A1319 ALERT**  **ALERT**