# Boeing Alert Service Bulletin 737-53A1409: Revision 1

- Rights: © The Boeing Company. Filed by the FAA in regulations.gov docket FAA-2026-1324; AD 2026-09-12 incorporates this document by reference. Not covered by OpenAirDocs’ CC0 dedication.
- Document: [Boeing Alert Service Bulletin 737-53A1409](https://openairdocs.org/service-documents/boeing/737-53a1409.md)
- Title as filed: SB_737-53A1409_Rev01
- Pages: 38
- PDF: https://openairdocs.org/files/sha256/12/a0/12a0f48bd15fcf5f03a69a11306994f7e1f57e86f96bd8d115b31bcb435b71bc
- Page: https://openairdocs.org/service-documents/boeing/737-53a1409/file/12a0f48bd15f

## Text

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### Page 1

Commercial 
Airplanes
737
Service Bulletin
ALERT
Number: 737-53A1409
Original Issue: May 04, 2023
Revision 1: October 27, 2023
ATA System: 5331
SUBJECT: FUSELAGE - Skin - Skin and Structure Common to the Aft Drain Mast - Inspection
EXPORT CONTROLLED - This technology or software is subject to the U.S. Export Administration Regulations
(EAR), (15 C.F.R. Parts 730-774). No authorization from the U.S. Department of Commerce is required for
export, re-export, in-country transfer, or access EXCEPT to country group E:1 or E:2 countries/persons per
Supp.1 to Part 740 of the EAR.
9E991ECCN:
BOEING PROPRIETARY
Copyright © 2023 The Boeing Company
Treatment of this document and its content is governed by contract with Boeing. Rights to use this document
are licensed on a per aircraft basis and such rights may not be transferable. For more information, contact The
Boeing Company.
Boeing, the Boeing signature, the Boeing symbol, 707, 717, 727, 737, 747, 757, 767, 777, 787, Dreamliner,
BBJ, DC-8, DC-9, DC-10, KC-10, KC-46, KDC-10, MD-10, MD-11, MD-80, MD-88, MD-90, P-8, Poseidon and
Boeing liveries are all trademarks owned by The Boeing Company; and no trademark license is granted in
connection with this document unless provided in writing by Boeing.
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
1 of 38
2.0

### Page 2

Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
2 of 38
BOEING SERVICE BULLETIN 737-53A1409
ALERTALERT
BLANK PAGE

### Page 3

Table of Contents
Revision Transmittal Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1. PLANNING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
A. Effectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Airplanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2. Spares Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
B. Concurrent Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
C. Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
D. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
E. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
F. Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
G. Manpower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
H. Weight and Balance Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
I. Electrical Load Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
J. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1. Existing Data: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2. Data Supplied with this Service Bulletin: . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3. Installation Drawings Used in the Preparation of this Service Bulletin: . . . . . . . . . . . 20
K. Publications Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
L. Interchangeability and Intermixability of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
M. Software Accomplishment Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2. MATERIAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
A. Material - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
B. Industry Support Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
C. Parts Necessary for Each Airplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Kits/Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2. Parts and Materials Supplied by the Operator . . . . . . . . . . . . . . . . . . . . . . . . 21
3. Parts Modified and Reidentified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4. Parts Removed and Not Replaced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
D. Parts Necessary to Change Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
E. Special Tooling - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
F. Special Tooling Necessary to do this Service Bulletin . . . . . . . . . . . . . . . . . . . . . . . 22
3. ACCOMPLISHMENT INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
A. GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
B. WORK INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
FIGURE 1: STRUCTURE COMMON TO THE AFT DRAIN MAST - INTERNAL DETAILED INSPECTION
[Group 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
FIGURE 2: FUSELAGE SKIN COMMON TO THE AFT DRAIN MAST - EXTERNAL DETAILED INSPECTION
AND EXTERNAL SURFACE HIGH FREQUENCY EDDY CURRENT INSPECTION [Group 2]
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS [Group 2] . . . . . . . . . . . . . . 31
APPENDIX A: SKIN AND STRUCTURE COMMON TO THE AFT DRAIN MAST INSPECTION [Group 2] . 37
Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
3 of 38
BOEING SERVICE BULLETIN 737-53A1409
ALERTALERT

### Page 4

Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
4 of 38
BOEING SERVICE BULLETIN 737-53A1409
ALERTALERT
BLANK PAGE

### Page 5

Commercial 
Airplanes
737
Service Bulletin
ALERT
Revision Transmittal SheetNumber: 737-53A1409Original Issue: May 04, 2023
Revision 1: October 27, 2023
ATA System: 5331
SUBJECT: FUSELAGE - Skin - Skin and Structure Common to the Aft Drain Mast - Inspection
This revision includes all pages of the service bulletin.
COMPLIANCE INFORMATION RELATED TO THIS REVISION
Effects of this Revision on airplanes on which Original Issue was previously done:
None.
Airplanes PA231-PA232, PC001-PC005, PG005, PG020-PG021, PG026, PG028-PG029, PG031, PG034-PG037,
PG041-PG043, PG046-PG050, PG055-PG056, PG058-PG059, PG064, PG073-PG074, PG199, PG201 -
PG230, PG251 - PG255, PG271 - PG279, PG301 - PG314, PG331 - PG332, PG351 - PG356, PG375, PG401
- PG403, PG431 - PG442, PG471 - PG475, PG501 - PG505, PG571 - PG583, PG584 - PG586, PG621 - PG630,
PG651 - PG652, PG701 - PG705, PH001, PH011 - PH013, PH021 - PH024, PH701 - PH715, PH731 - PH732,
PH741 - PH742, PH743, PJ001 - PJ002, PJ031 - PJ032, PJ071 - PJ072, PJ101 - PJ104, PJ105 - PJ113, PK026
- PK029, PK041 - PK053, PK061 - PK070, PK081 - PK082, PK091 - PK099, PK101 - PK103, PK111 - PK120,
PK141 - PK146, PK203 - PK204, PK211 - PK223, PK231 - PK241, PK251 - PK258, PK271 - PK274, PK291,
PK301 - PK318, PK341, PK361, PK431 - PK433, PK451 - PK452, PK511 - PK515, PK519, PK521 - PK528,
PK541 - PK565, PK581, PK591 - PK599, PK601 - PK610, PK641 - PK642, PK661 - PK666, PK691 - PK697,
PK711 - PK716, PK861 - PK863, PK881 - PK884, PL001, PL025 - PL028, PL061, PL101 - PL113, PL151, PL171
- PL172, PL201 - PL203, PL421, PL441, PL491, PL501 - PL506, PL581, PL601 - PL603, PL611, PL621 - PL623,
PL711 - PL712, PL716, PL717 - PL735, PL756, PL758, PL761, PL781 - PL782, PL793, PL801 - PL803, PM001
- PM006, PM016 - PM017, PM021 - PM023, PM051 - PM066, PM101 - PM119, PM181, PN131 - PN163, PN401
- PN420, PN431 - PN433, PN481, PN491 - PN493, PN511 - PN512, PP101 - PP169, PP181 - PP199, PP376
- PP383, PP521 - PP522, PP631 - PP634, PP651 - PP652, PP771 - PP779, PP891 - PP899, PP901 - PP903,
PP991, PQ221 - PQ237, PS651 - PS657, PS666 - PS668, PS751 - PS799, PS901 - PS941, PU001 - PU025,
PX071, PX701, PY001 - PY008, PY021, PY022, PY031, PY036 - PY037, PY046 - PY048, PY051 - PY053,
PY131 - PY135, PY141 - PY143, PY156 - PY157, PY161 - PY162, PY166, PY191, PY221 - PY222, PY241 -
PY244, PY270 - PY275, PY281, PY286, PY301 - PY304, PY321 - PY323, PY341 - PY346, PY361 - PY362,
PY381, PY401, PY409 - PY411, PY421 - PY422, PY441, PY451, PY591 - PY595, PY611 - PY612, PY621,
PY631, PY651, PY671 - PY672 and PY741 were removed from Group 1 and Group 2 of this service bulletin
effectivity.
REASON FOR REVISION
This revision is sent to remove airplanes from the effectivity that do not have an aft waste water drain mast
installed.
These sections were changed:
Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
5 of 38

### Page 6

1. In Summary, Effectivity, updated effectivity statement.
2. In Paragraph 1.A., Effectivity, removed airplanes and changed Group Configuration descriptions.
3. In Paragraph 1.C., Reason, added Revision 1 statement.
4. In Paragraph 1.D., Description, added Revision 1 statement.
5. In Paragraph 2.C.2., Parts and Materials Supplied by the Operator, added information.
Vertical lines are put on the left edge of each page, except in Paragraph 1.A., Effectivity and format changes,
to show the location of all content changes.
Pages with no vertical lines have no changes.
REVISION HISTORY
May 04, 2023Original Issue:
October 27, 2023Revision 1:
Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
6 of 38
BOEING SERVICE BULLETIN 737-53A1409
ALERTALERT

### Page 7

Commercial 
Airplanes
737
Service Bulletin
ALERT
SummaryNumber: 737-53A1409Original Issue: May 04, 2023
Revision 1: October 27, 2023
ATA System: 5331
SUBJECT: FUSELAGE - Skin - Skin and Structure Common to the Aft Drain Mast - Inspection
THIS DOCUMENT IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN
PARAGRAPH 1.A., EFFECTIVITY. IF AN AIRPLANE HAS BEEN LEASED OR SOLD, SEND THIS DOCUMENT
TO THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS DOCUMENT TO THE
NEW OWNER.
CONCURRENT REQUIREMENTS
None.
BACKGROUND
Accomplishment of this service bulletin will make sure that any crack and any corrosion in the fuselage skin or
structure common to the aft drain mast is found and repaired before it reaches a critical length. If the work given
in this service bulletin is not done, any undetected crack in the fuselage skin common to the aft drain mast could
result in the inability of the Principal Structural Element (PSE) to sustain limit loads, and may result in a rapid
decompression of the fuselage and the loss of structural integrity of the airplane.
An operator of a 737-400 airplane reported two cracks of 0.4 inches and 0.6 inches in length, located in the
fuselage skin underneath the aft drain mast. The cracks were found when an inspection was done in accordance
with Boeing Service Bulletin 737-53A1318, which provides inspection instructions to make sure the drain mast
is installed correctly. The reported cracks were found on an airplane that had the drain mast correctly installed
and had accumulated 30,684 flight hours and 30,735 flight cycles. Boeing has determined that cracks in this
location could be caused by local elevated skin stress from the elliptical cutout, aerodynamic loading effects
and minor skin defects.
This service bulletin gives instructions to inspect the skin and structure common to the aft drain mast for any
crack and any corrosion and to do on-condition actions.
Boeing Service Related Problem (SRP) 737-SRP-53-0646 is related to this service bulletin.
Boeing Fleet Team Digest (FTD) 737-FTD-53-21002 is related to this service bulletin.
Boeing Service Bulletin 737-53A1318 is related to this service bulletin.
This table is provided to operators for planning purposes only. Refer to the applicable sections for more
information.
Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
7 of 38

### Page 8

ReferenceAffectedPlanning Data
Paragraph 1.A.2., Spares AffectedNoSpares Affected
Paragraph 1.E., Compliance and Paragraph
1.F., Approval
NoAD Related
Paragraph 1.H., Weight and Balance ChangesNoWeight and Balance Change
Paragraph 1.I., Electrical Load DataNoElectrical Load Changed
Paragraph 1.K., Publications AffectedNoPublications Affected
Paragraph 1.K., Publications AffectedNoAirplane Flight Operations Affected (Flight Crew
Operations Manual and/or FAA Approved Air-
plane Flight Manual)
Paragraph 2.C.1., Kits/PartsNoKits/Parts Required
Paragraph 2.C.2., Parts and Materials Supplied
by the Operator
NoOperator Supplied Parts/Material
Paragraph 2.F., Special Tooling Necessary to
do this Service Bulletin
NoSpecial Tooling Required
ACTION
Group 1:
Boeing endorses the FAA rules related to Limit of Validity (LOV) and recommends immediate and permanent
removal from service of any airplanes upon reaching the LOV, whether or not it is operated under FAA jurisdiction.
As such, Boeing no longer provides maintenance instructions for airplanes that have accumulated flight cycles
beyond the LOV. Airplanes in Group 1 (line numbers 1-291) have accumulated flight cycles beyond the LOV of
the maintenance program. 14 CFR 121.1115 and 129.115 prohibit operation of an airplane beyond its LOV.
Group 2:
Do an internal detailed inspection around the fastener holes, cutout, channel, and fillers for any crack and any
corrosion. Do an external detailed inspection and external surface High Frequency Eddy Current (HFEC)
inspection on the fuselage skin around the fastener holes and cutout for any crack and any corrosion. If any
crack or any corrosion is found contact The Boeing Company for repair instructions and do the repair. If no crack
and no corrosion is found, repeat the internal and external detailed inspections and external surface High
Frequency Eddy Current (HFEC) inspection for any crack and corrosion.
EFFECTIVITY
737-100/200/200C/300/400/500 Airplanes. Refer to Paragraph 1.A.1., Airplanes, for the list of affected airplanes.
COMPLIANCE
Refer to Paragraph 1.E., Compliance.
INDUSTRY SUPPORT INFORMATION
Boeing warranty remedies are not available for the inspection and/or repairs given in this service bulletin.
Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
8 of 38
BOEING SERVICE BULLETIN 737-53A1409
ALERTALERT

### Page 9 (OCR)

BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
MANPOWER
Refer to Paragraph 1.G., Manpower.
MATERIAL INFORMATION
None.
DO AN INTERNAL DETAILED INSPECTION OF THE FASTENER HOLES, CUTOUT
CHANNEL, AND FILLERS FOR ANY CRACK AND ANY CORROSION. DO AN EXTERNAL
DETAILED INSPECTION AND EXTERNAL SURFACE HIGH FREQUENCY EDDY
CURRENT (HFEC) INSPECTION ON THE SKIN AROUND THE FASTENER HOLES AND
CUTOUT FOR ANY CRACK AND ANY CORROSION. IF ANY CRACK OR ANY
CORROSION IS FOUND CONTACT THE BOEING COMPANY FOR REPAIR
INSTRUCTIONS AND DO THE REPAIR.
3021215
Original Issue: May 04, 2023
Revision 1: October 27, 2023  Export Controlled ECCN: 9E991  737-53A1409
BOEING PROPRIETARY - See page 1 for details  9 of 38

### Page 10

Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
10 of 38
BOEING SERVICE BULLETIN 737-53A1409
ALERTALERT
BLANK PAGE

### Page 11

Commercial 
Airplanes
737
Service Bulletin
ALERT
Number: 737-53A1409
Original Issue: May 04, 2023
Revision 1: October 27, 2023
ATA System: 5331
SUBJECT: FUSELAGE - Skin - Skin and Structure Common to the Aft Drain Mast - Inspection
THIS DOCUMENT IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN
PARAGRAPH 1.A., EFFECTIVITY. IF AN AIRPLANE HAS BEEN LEASED OR SOLD, SEND THIS DOCUMENT
TO THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS DOCUMENT TO THE
NEW OWNER.
1.    PLANNING INFORMATION
A. Effectivity
1. Airplanes
This bulletin is applicable to 737-100, 737-200, 737-200C, 737-300, 737-400, 737-500 Airplane(s),
line number(s) 1-12, 14-15, 17, 19, 21-28, 30-32, 34-37, 42, 48, 52, 55, 58-59, 62, 65, 74, 76, 85,
98-99, 103, 106, 108, 113, 116-120, 127, 133, 135, 137-138, 150, 174-175, 179, 183, 186-187,
191, 197-198, 200-202, 211, 302-303, 305-308, 310, 315, 317, 320, 326, 329-330, 333-337,
339-340, 343, 345-350, 354-355, 357, 359, 362-363, 370, 372, 391, 395, 405, 408, 425, 427, 436,
440, 460, 462, 479-481, 483, 493, 496-498, 500, 506-507, 510, 512, 517-518, 521, 523, 525,
527-528, 530, 536-540, 549-552, 555-560, 563-564, 566, 569-570, 572, 574-575, 577, 581-582,
584, 595-596, 598-599, 601, 612, 614, 616, 620-621, 623-629, 631-633, 635-637, 641-650,
652-654, 656-662, 664, 666-670, 672-673, 677, 684, 686, 688, 690, 693-694, 696-705, 707-710,
712-718, 720-723, 726-727, 729-730, 734-735, 737, 740, 742-746, 749-757, 760-762, 764-765,
767-772, 774, 777-778, 781, 783-786, 788-791, 793, 795, 797, 801, 803-804, 806, 808, 810,
812-813, 815, 817-819, 822-825, 831-832, 838, 840, 847-850, 855-856, 858, 861-863, 866-867,
871-872, 874-876, 884-886, 888, 890, 893, 895, 897-898, 900-901, 904, 906, 908, 910-911, 915,
917, 919-922, 925-927, 930-931, 934-937, 939, 941, 943-946, 948, 950, 952-953, 956, 958-960,
962, 966-967, 971-974, 976, 978-979, 981, 983, 986, 988-990, 992, 997-999, 1001-1002, 1007,
1015, 1022, 1030, 1032, 1039, 1043-1044, 1047, 1049-1050, 1053-1058, 1060, 1064, 1067, 1069,
1073-1075, 1077-1083, 1085-1089, 1091-1093, 1097-1099, 1102-1112, 1114-1116, 1118-1124,
1126-1127, 1129-1133, 1135, 1137, 1140-1147, 1149-1155, 1157-1159, 1162, 1164-1165, 1167,
1169-1170, 1172-1174, 1176-1181, 1188, 1190-1192, 1195, 1198, 1200, 1202, 1204, 1206-1208,
1210, 1212-1214, 1216-1223, 1225-1228, 1230, 1233-1236, 1238-1239, 1242-1248, 1250-1251,
1253-1254, 1256, 1258-1260, 1262-1264, 1266-1282, 1285-1298, 1300-1301, 1303, 1306-1309,
1314-1317, 1319-1320, 1322-1328, 1330-1336, 1338-1341, 1343, 1345-1346, 1349, 1352-1360,
1362-1368, 1370, 1372-1376, 1380-1383, 1385-1386, 1388-1391, 1393-1397, 1401-1402, 1404,
1406, 1408, 1410-1414, 1416, 1418, 1420, 1425-1435, 1437, 1439-1454, 1458, 1460-1466,
1468-1481, 1483, 1485, 1487-1493, 1495, 1497-1520, 1522-1523, 1527-1528, 1530, 1532, 1534,
1538-1544, 1546, 1548, 1550-1552, 1554-1556, 1558-1564, 1566, 1568-1570, 1572-1575, 1577,
1579-1582, 1584-1590, 1592, 1594-1605, 1607, 1609-1611, 1613, 1615-1623, 1625, 1627, 1629,
Export Controlled ECCN: 9E991
BOEING PROPRIETARY - See page 1 for details
Original Issue: May 04, 2023
737-53A1409Revision 1: October 27, 2023
11 of 38

### Page 12

1631-1661, 1663-1674, 1676-1681, 1683-1685, 1687, 1691-1707, 1709, 1711-1716, 1720-1733,
1735-1743, 1745-1747, 1749-1765, 1767-1789, 1791-1803, 1805-1808, 1810-1822, 1824,
1827-1842, 1844-1851, 1853-1863, 1865-1868, 1870-1883, 1885-1894, 1896-1931, 1933,
1935-1939, 1941, 1943-1946, 1948-1990, 1992-2003, 2006, 2008-2016, 2018-2023, 2025-2028,
2030-2036, 2038, 2040-2052, 2054-2055, 2057, 2059-2077, 2079, 2081-2091, 2093-2102, 2104,
2106-2120, 2122-2133, 2135, 2137-2201, 2203, 2205-2223, 2225-2282, 2284, 2286, 2288-2291,
2293, 2296, 2298-2306, 2308, 2310-2321, 2323-2428, 2431-2432, 2434-2468, 2471-2472,
2474-2476, 2478-2496, 2498-2499, 2501-2503, 2505-2508, 2510-2514, 2516-2519, 2521-2569,
2571-2578, 2581-2609, 2614-2616, 2618-2625, 2630-2641, 2646-2666, 2669-2694, 2698,
2700-2701, 2703-2712, 2717-2739, 2743, 2746-2749, 2751-2752, 2756, 2760, 2763-2765,
2768-2778, 2782-2786, 2788, 2791-2794, 2800-2806, 2809-2812, 2815-2818, 2822-2839,
2844-2868, 2872-2891, 2895-2900, 2902-2914, 2919-2930, 2933-3132 in 2 Group(s). Where the
effectivity is presented with hyphens between line numbers, the airplane applicability means
"through" and "inclusive", e.g. line numbers 1-9 means line numbers 1 through 9 inclusive.
Refer to Service Bulletin Index D6-19567 Part 3 for Airplane Variable Number, Line Number, and
Serial Number data.
The Variable Numbers and Group Information for the applicable airplanes is given below.
DESCRIPTIONCONFIGURATIONGROUP
737-100/200/200C Airplanes with an aft waste water drain mast
installed, line numbers 1-291 beyond the Limit of Validity (LOV).
-1
737-200/200C/300/400/500 Airplanes with an aft waste water drain
mast installed, line numbers 292-3132.
-2
Airplane Models:
737-100, 737-200, 737-200C, 737-300, 737-400, 737-500
GroupVariable Number
1PA001 - PA022
1PA099
1PG001 - PG004
1PG006 - PG019
1PG022 - PG025
1PG027
1PG030
1PG032 - PG033
1PG038 - PG040
1PG044 - PG045
1PG051 - PG054
GroupVariable Number
1PG057
1PG060 - PG063
1PG065 - PG072
1PG075
2PJ003 - PJ009
2PJ114 - PJ119
2PJ201 - PJ219
2PJ301 - PJ302
2PJ551 - PJ561
2PJ601 - PJ615
2PJ811
GroupVariable Number
2PJ816 - PJ817
2PK201 - PK202
2PK281 - PK289
2PK351 - PK360
2PK391
2PK461 - PK469
2PK495
2PK501 - PK504
2PK611 - PK617
2PK621 - PK637
2PK671 - PK681
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GroupVariable Number
2PK731 - PK765
2PK771 - PK779
2PK801 - PK804
2PK819 - PK827
2PK830
2PK871 - PK874
2PK901 - PK938
2PK971 - PK974
2PL002 - PL024
2PL081
2PL221
2PL401 - PL417
2PL451 - PL456
2PL471
2PL551 - PL562
2PL624 - PL626
2PL631 - PL632
2PL736 - PL747
2PL762 - PL770
2PL783 - PL788
2PM141 - PM142
2PM171
2PM251 - PM255
2PM281 - PM283
2PM381 - PM399
2PM401 - PM417
2PM541 - PM564
2PN001 - PN002
2PN021 - PN043
2PN081 - PN086
2PN101 - PN117
2PN451 - PN456
2PN471 - PN474
GroupVariable Number
2PN501 - PN502
2PN521
2PP001 - PP054
2PP201 - PP205
2PP221
2PP231 - PP243
2PP281 - PP286
2PP301 - PP305
2PP351 - PP353
2PP384
2PP391 - PP393
2PP401 - PP440
2PP471 - PP475
2PP501 - PP520
2PP671 - PP699
2PP701 - PP733
2PP801 - PP808
2PP821 - PP827
2PP831 - PP848
2PP851 - PP852
2PP861 - PP877
2PP904 - PP936
2PP946 - PP948
2PP951 - PP952
2PP961 - PP967
2PP981 - PP990
2PP993
2PQ001 - PQ016
2PQ026 - PQ041
2PQ051 - PQ092
2PQ101 - PQ199
2PQ201 - PQ202
2PQ241 - PQ243
GroupVariable Number
2PQ251 - PQ267
2PQ281 - PQ299
2PQ301 - PQ307
2PQ331 - PQ332
2PQ341 - PQ348
2PQ361 - PQ373
2PQ391 - PQ395
2PQ401 - PQ418
2PQ421
2PQ431 - PQ438
2PQ447 - PQ448
2PQ451
2PQ454
2PQ471 - PQ475
2PQ479 - PQ481
2PQ486 - PQ487
2PQ491 - PQ493
2PQ771 - PQ772
2PQ791 - PQ793
2PQ801 - PQ805
2PQ931 - PQ935
2PQ951
2PQ971 - PQ997
2PR001 - PR017
2PR021 - PR034
2PR041 - PR045
2PR061 - PR072
2PR077 - PR082
2PR091 - PR092
2PR096
2PR101
2PR121 - PR122
2PR131 - PR132
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GroupVariable Number
2PR141 - PR143
2PR161 - PR172
2PR181
2PS601 - PS631
2PS636 - PS638
2PS641 - PS644
2PS669
2PS691 - PS692
2PS701 - PS706
2PS811
2PS836 - PS837
2PS841 - PS846
2PS851 - PS852
2PS856
2PS861 - PS863
2PS866 - PS868
2PS871 - PS874
2PS896 - PS897
2PS956 - PS957
2PS961 - PS963
2PS971 - PS978
2PT001 - PT015
2PT021 - PT031
2PT041 - PT064
2PT101 - PT105
2PT121 - PT138
2PT146 - PT148
2PT161 - PT170
2PT181 - PT188
2PT211 - PT220
2PT295
2PT301 - PT309
2PT331 - PT360
GroupVariable Number
2PT381 - PT399
2PT401 - PT438
2PT501 - PT517
2PT561 - PT565
2PT581 - PT586
2PT611 - PT621
2PT641 - PT644
2PT651 - PT656
2PT671 - PT672
2PT681 - PT685
2PT701 - PT703
2PT716 - PT717
2PT721 - PT725
2PT801 - PT834
2PT851 - PT854
2PT871 - PT886
2PT901 - PT930
2PT971 - PT973
2PT981 - PT985
2PT996
2PU301
2PU311 - PU313
2PV001 - PV055
2PV201 - PV209
2PV226 - PV229
2PV231 - PV237
2PV271 - PV272
2PV281 - PV287
2PV296
2PV301 - PV302
2PV351
2PV356 - PV357
2PW001 - PW054
GroupVariable Number
2PW061 - PW068
2PW072
2PW086 - PW088
2PW091 - PW094
2PW101 - PW102
2PW106
2PW111 - PW120
2PW156 - PW157
2PW161 - PW171
2PW201 - PW252
2PW261 - PW268
2PW271 - PW276
2PW278
2PW281 - PW293
2PW296
2PW301 - PW327
2PW401 - PW408
2PW411 - PW418
2PW421 - PW424
2PW431 - PW435
2PW441 - PW450
2PW461 - PW467
2PW501 - PW504
2PW511 - PW522
2PW524 - PW550
2PW556 - PW557
2PW561 - PW564
2PW571 - PW576
2PW591 - PW596
2PW611 - PW622
2PW631 - PW637
2PW661 - PW662
2PW681 - PW683
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GroupVariable Number
2PW701 - PW702
2PW711 - PW717
2PW741 - PW742
2PW761
2PW771
GroupVariable Number
2PW831
2PW851 - PW856
2PY056 - PY057
2PY101 - PY103
2PY111 - PY113
GroupVariable Number
2PY151 - PY154
2PY201
2PY231
2PY461 - PY463
2PY721
2. Spares Affected
None.
B. Concurrent Requirements
None.
C. Reason
Accomplishment of this service bulletin will make sure that any crack and any corrosion in the fuselage
skin or structure common to the aft drain mast is found and repaired before it reaches a critical length.
If the work given in this service bulletin is not done, any undetected crack in the fuselage skin common
to the aft drain mast could result in the inability of the Principal Structural Element (PSE) to sustain
limit loads, and may result in a rapid decompression of the fuselage and the loss of structural integrity
of the airplane.
An operator of a 737-400 airplane reported two cracks of 0.4 inches and 0.6 inches in length, located
in the fuselage skin underneath the aft drain mast. The cracks were found when an inspection was
done in accordance with Boeing Service Bulletin 737-53A1318, which provides inspection instructions
to make sure the drain mast is installed correctly. The reported cracks were found on an airplane that
had the drain mast correctly installed and had accumulated 30,684 flight hours and 30,735 flight cycles.
Boeing has determined that cracks in this location could be caused by local elevated skin stress from
the elliptical cutout, aerodynamic loading effects and minor skin defects.
This service bulletin gives instructions to inspect the skin and structure common to the aft drain mast
for any crack and any corrosion and to do on-condition actions.
Boeing Service Related Problem (SRP) 737-SRP-53-0646 is related to this service bulletin.
Boeing Fleet Team Digest (FTD) 737-FTD-53-21002 is related to this service bulletin.
Boeing Service Bulletin 737-53A1318 is related to this service bulletin.
Revision 1 is sent to remove airplanes from the effectivity that do not have an aft waste water drain
mast installed.
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D. Description
Group 1:
Boeing endorses the FAA rules related to Limit of Validity (LOV) and recommends immediate and
permanent removal from service of any airplanes upon reaching the LOV, whether or not it is operated
under FAA jurisdiction. As such, Boeing no longer provides maintenance instructions for airplanes that
have accumulated flight cycles beyond the LOV. Airplanes in Group 1 (line numbers 1-291) have
accumulated flight cycles beyond the LOV of the maintenance program. 14 CFR 121.1115 and 129.115
prohibit operation of an airplane beyond its LOV.
Group 2:
Do an internal detailed inspection around the fastener holes, cutout, channel, and fillers for any crack
and any corrosion. Do an external detailed inspection and external surface High Frequency Eddy
Current (HFEC) inspection on the fuselage skin around the fastener holes and cutout for any crack
and any corrosion. If any crack or any corrosion is found contact The Boeing Company for repair
instructions and do the repair. If no crack and no corrosion is found, repeat the internal and external
detailed inspections and external surface High Frequency Eddy Current (HFEC) inspection for any
crack and corrosion.
Effects of this Revision on airplanes on which Original Issue was previously done:
None.
The work in this service bulletin is done in the maintenance zone(s) given below.
Group 1:
Affected Maintenance Zones
ZoneModel
2-20737-100, 737-200
Group 2:
Affected Maintenance Zones
ZoneModel
2-20737-200, 737-200C
Group 2:
Affected Maintenance Zones
ZoneModel
220737-300, 737-400, 737-500
E. Compliance
Accomplish the required actions, based on the applicable conditions in Table 1, in accordance with
Paragraph 3. Accomplishment Instructions.
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When more than one OPTION is given for a CONDITION, do only one of the OPTION numbers. When
more than one ACTION is given for a CONDITION or an OPTION, do all of the ACTION numbers for
that CONDITION or OPTION.
Group 1:
Boeing endorses the FAA rules related to Limit of Validity (LOV) and recommends immediate and
permanent removal from service of any airplanes upon reaching the LOV, whether or not it is operated
under FAA jurisdiction. As such, Boeing no longer provides maintenance instructions for airplanes that
have accumulated flight cycles beyond the LOV. Airplanes in Group 1 (line numbers 1-291) have
accumulated flight cycles beyond the LOV of the maintenance program. 14 CFR 121.1115 and 129.115
prohibit operation of an airplane beyond its LOV.
Group 2:
Table 1: Skin and Structure Common to the Aft Drain Mast Inspection
Repeat Interval
(Not to Exceed)
Boeing Recommended
Compliance Time (Whichever
Occurs Later)
ActionCondition
-Within 2,500
flight cycles af-
ter the Original
Issue date of
Service Bulletin
SB 737-
53A1409.
Before 25,000
total flight cy-
cles.
ACTION 1: Do PART 2:
Internal detailed inspec-
tion around the fastener
holes, cutout, channel,
and fillers for any crack
and any corrosion.
All Airplanes.
ACTION 2: Do PART 3:
External detailed inspec-
tion and external surface
High Frequency Eddy
Current (HFEC) inspec-
tion on the fuselage skin
around the fastener holes
and cutout for any crack
and any corrosion.
-Before further flight.Contact The Boeing
Company for repair in-
structions and do the re-
pair.
CONDITION 1: ANY
CRACK OR ANY CORRO-
SION FOUND AS A RE-
SULT OF INTERNAL DE-
TAILED INSPECTION (a)
12,000 flight cycles
or 6 years,
whichever occurs
first.
-Repeat PART 2: Internal
detailed inspection
around the fastener
holes, cutout, channel,
and fillers for any crack
and any corrosion.
CONDITION 2: NO
CRACK AND NO CORRO-
SION FOUND AS A RE-
SULT OF INTERNAL DE-
TAILED INSPECTION (a)
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Group 2:
Table 1: Skin and Structure Common to the Aft Drain Mast Inspection
Repeat Interval
(Not to Exceed)
Boeing Recommended
Compliance Time (Whichever
Occurs Later)
ActionCondition
-Before further flight.Contact The Boeing
Company for repair in-
structions and do the re-
pair.
CONDITION 3: ANY
CRACK OR ANY CORRO-
SION FOUND AS A RE-
SULT OF EXTERNAL DE-
TAILED AND HFEC IN-
SPECTION (a)
12,000 flight cycles
or 6 years,
whichever occurs
first.
-Repeat PART 3: External
detailed inspection and
external surface High
Frequency Eddy Current
(HFEC) inspection on the
fuselage skin around the
fastener holes and cutout
for any crack and any
corrosion.
CONDITION 4: NO
CRACK AND NO CORRO-
SION FOUND AS A RE-
SULT OF EXTERNAL DE-
TAILED AND HFEC IN-
SPECTION (a)
(a) More than one CONDITION can be applicable on each airplane.
F. Approval
This service bulletin contains no information that changes the approved configuration of the airplane.
Therefore, you can use the information in this service bulletin without regulatory agency approval.
G. Manpower
The table below shows an estimate of the task hours necessary to do this inspection 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
Group 2:
Skin and Structure Common to the Aft Drain Mast Inspection
Elapsed HoursTask HoursNumber of PersonsTask
1.31.31Open Access
1.01.01FIGURE 1
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Group 2:
Skin and Structure Common to the Aft Drain Mast Inspection
Elapsed HoursTask HoursNumber of PersonsTask
2.02.01FIGURE 2
1.51.51FIGURE 3
0.80.81Close Access
6.66.6TOTAL FOR EACH AIRPLANE
H. Weight and Balance Changes
None.
I. Electrical Load Data
Not changed.
J. References
1. Existing Data:
a. Boeing Service Bulletin 737-53A1318
b. Boeing Service Letter 737-SL-51-042
c. Boeing Service Related Problem (SRP) 737-SRP-53-0646
d. Service Bulletin Index D6-19567
e. Standard Overhaul Practices Manual (SOPM) 20-11-03, 20-30-03, 20-41-02, 20-41-05,
20-43-03, 20-50-01, 20-50-19
f. 737 Non-Destructive Testing (NDT) Manual Part 6, 51-00-00 Procedure 4, 737 NDT Manual
Part 6, 51-00-00 Procedure 23.
g. 737-100/200/300/400/500 Fleet Team Digest (FTD) 737-FTD-53-21002
h. 737-100/200 Aircraft Maintenance Manual (AMM) 25-52-131, 25-52-141, 30-71-00, 38-31-21,
51-31-00
i. 737-300/400/500 Aircraft Maintenance Manual (AMM) 25-52-81, 25-52-91, 30-71-00, 38-31-21,
51-31-00
j. Standard Wiring Practices Manual (SWPM) 20-20-00, 20-20-10
2. Data Supplied with this Service Bulletin:
None.
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3. Installation Drawings Used in the Preparation of this Service Bulletin:
None.
K. Publications Affected
1. Publications:
None.
2. Damage Tolerance Based Structural Inspections:
This service bulletin affects Fatigue Critical Structure (FCS) but does not contain repairs or changes.
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.
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2.    MATERIAL INFORMATION
A. Material - Price and Availability
None.
B. Industry Support Information
Boeing warranty remedies are not available for the inspection and/or repairs given in 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 given 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.
NotesNameQTYPart Number /
Specification
(a)(c)(d)Chemical Conversion Coating5 OzType 2, Class A
(b)(c)(e)Primer5 OzBMS 10-11, Type I
(b)(c)Sealant10 OzBMS 5-95, Type 1,
Class B-1/2 or
Class B-2
(b)(c)Corrosion Inhibiting Compound15 OzBMS 3-29
(a) Refer to SOPM 20-43-03 for material sources.
(b) Refer to the Qualified Products List at the end of the Boeing Material Specification (BMS)
for supplier data.
(c) Can be purchased from: Boeing Distribution Services Inc (cage code: 2N935). 3760 W.
108th Street, Miami, FL 33018 USA. Website: https://www.boeingdistribution.com. Tele-
phone: +1-305-925-2600. Fax: +1-305-507-7191. AOG: +1-305-471-8888. Email: Your
BDSI customer representative or AOGdesk@Boeingdistribution.com.
(d) Some conversion coatings contain Chromium trioxide/Chromic acid and will not be
available in the European Union after September 2017 without an authorization. EU op-
erators are encouraged to ensure their suppliers are authorized to provide the material
after the sunset date and that downstream users comply with the risk mitigation measures
and operational conditions
(e) Some primers contain Strontium Chromate and will not be available in the European
Union after January 2019 without an authorization. EU operators are encouraged to ensure
their suppliers are authorized to provide the material after the sunset date and that
downstream users comply with the risk mitigation measures and operational conditions.
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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.
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3.    ACCOMPLISHMENT INSTRUCTIONS
A. GENERAL INFORMATION
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.
CAUTION
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 Values:
— Values for structural fasteners are given in 737 Structural Repair Manual,
Chapter 51.
— Values for airframe maintenance tasks are included in Chapter 20 of 737
Aircraft Maintenance Manual (AMM).
4. Use the approved fastener, process and material substitutions in accordance with
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 in accordance with SRM Chapter 51. Refer to SOPM 20-50-01 for alternate
full threaded fasteners (screws) needed for installation in this service bulletin.
6. A Detailed Inspection is defined as: An intensive examination of a specific item,
installation, or assembly to detect damage, failure, or irregularity. This could include
tactile assessment in which a component or assembly can be checked for
tightness/security. 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.
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7. 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.
8. 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.
9. Refer to APPENDIX A for logic diagram. Logic diagrams are provided as an aid only.
Information contained in Paragraph 1.E., Compliance is the primary source for
compliance times. Information in Paragraph 3.B., Work Instructions is the primary
source for tasks required for compliance.
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. Use of colors in Figures is based on guidance from the ATA e-Business Program
(ATA) iSpec 2200.
14. When more than one OPTION is given for a CONDITION, do only one of the OPTION
numbers. When more than one ACTION is given for a CONDITION or an OPTION,
do all of the ACTION numbers for that CONDITION or OPTION.
15. The compliance times for the actions in Paragraph 3.B., WORK INSTRUCTIONS
are in Paragraph 1.E., Compliance.
B. WORK INSTRUCTIONS
Group 1:
Boeing endorses the FAA rules related to Limit of Validity (LOV) and recommends immediate and
permanent removal from service of any airplanes upon reaching the LOV, whether or not it is operated
under FAA jurisdiction. As such, Boeing no longer provides maintenance instructions for airplanes that
have accumulated flight cycles beyond the LOV. Airplanes in Group 1 (line numbers 1-291) have
accumulated flight cycles beyond the LOV of the maintenance program. 14 CFR 121.1115 and 129.115
prohibit operation of an airplane beyond its LOV.
Group 2:
Skin and Structure Common to the Aft Drain Mast Inspection
1. Do PART 1: OPEN ACCESS.
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BOEING SERVICE BULLETIN 737-53A1409
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2. ACTION 1: Do PART 2: INTERNAL DETAILED INSPECTION AROUND THE FASTENER HOLES,
CUTOUT, CHANNEL, AND FILLERS FOR ANY CRACK AND ANY CORROSION.
a. CONDITION 1: ANY CRACK OR ANY CORROSION FOUND AS A RESULT OF INTERNAL
DETAILED INSPECTION
(1) Contact The Boeing Company for repair instructions and do the repair.
b. CONDITION 2: NO CRACK AND NO CORROSION FOUND AS A RESULT OF INTERNAL
DETAILED INSPECTION
(1) Repeat PART 2: INTERNAL DETAILED INSPECTION AROUND THE FASTENER
HOLES, CUTOUT, CHANNEL, AND FILLERS FOR ANY CRACK AND ANY CORROSION.
3. ACTION 2: Do PART 3: EXTERNAL DETAILED INSPECTION AND EXTERNAL SURFACE HIGH
FREQUENCY EDDY CURRENT (HFEC) INSPECTION ON THE FUSELAGE SKIN AROUND
THE FASTENER HOLES AND CUTOUT FOR ANY CRACK AND ANY CORROSION.
a. CONDITION 3: ANY CRACK OR ANY CORROSION FOUND AS A RESULT OF EXTERNAL
DETAILED AND HFEC INSPECTION
(1) Contact The Boeing Company for repair instructions and do the repair.
b. CONDITION 4: NO CRACK AND NO CORROSION FOUND AS A RESULT OF EXTERNAL
DETAILED AND HFEC INSPECTION
(1) Repeat PART 3: EXTERNAL DETAILED INSPECTION AND EXTERNAL SURFACE
HIGH FREQUENCY EDDY CURRENT (HFEC) INSPECTION ON THE FUSELAGE SKIN
AROUND THE FASTENER HOLES AND CUTOUT FOR ANY CRACK AND ANY
CORROSION.
4. Do PART 4: CLOSE ACCESS.
Group 2:
PART 1: OPEN ACCESS.
1. Get access to the aft cargo compartment aft bulkhead.
2. Remove and keep the center panel from the aft cargo compartment aft bulkhead. Refer to
737-100/200 AMM 25-52-131 and 737-300/400/500 AMM 25-52-81 as an accepted procedure.
3. If required, remove and keep insulation. Refer to 737-100/200 AMM 25-52-141 and 737-300/400/500
AMM 25-52-91 as an accepted procedure.
4. Remove and keep drain mast. Refer to 737-100/200 AMM 38-31-21 and 737-300/400/500 AMM
38-31-21 as an accepted procedure.
Group 2:
PART 2: INTERNAL DETAILED INSPECTION AROUND THE FASTENER HOLES, CUTOUT,
CHANNEL, AND FILLERS FOR ANY CRACK AND ANY CORROSION.
1. Do an internal detailed inspection around the fastener holes, cutout, channel, and fillers for any
crack and any corrosion in accordance with FIGURE 1.
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737-53A1409Revision 1: October 27, 2023
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BOEING SERVICE BULLETIN 737-53A1409
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Group 2:
PART 3: EXTERNAL DETAILED INSPECTION AND EXTERNAL SURFACE HIGH FREQUENCY
EDDY CURRENT (HFEC) INSPECTION ON THE FUSELAGE SKIN AROUND THE FASTENER
HOLES AND CUTOUT FOR ANY CRACK AND ANY CORROSION.
1. Do an external detailed and HFEC inspection on the fuselage skin around the fastener holes and
cutout for any crack and any corrosion in accordance with FIGURE 2.
Group 2:
PART 4: CLOSE ACCESS.
1. Close access to the aft waste water drain mast in accordance with FIGURE 3.
2. Put the airplane back to a serviceable condition.
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BOEING SERVICE BULLETIN 737-53A1409
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BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
This Figure applies only to: Group 2.
FWD
AFT DRAIN MAST
S-24L
VIEW LOOKING DOWN
A-A
CRACK IN CHANNEL
AND FILLER
(TYPICAL)
VIEW OF DRAIN MAST SUPPORT STRUCTURE
(SOME STRUCTURE NOT SHOWN FOR CLARITY)
INTERNAL DETAILED INSPECTION OF FILLER AND FASTENER HOLES  INTERNAL DETAILED INSPECTION OF CHANNEL AND CUTOUT  3023305
FIGURE 1: STRUCTURE COMMON TO THE AFT DRAIN MAST - INTERNAL DETAILED INSPECTION
(SHEET 1 OF 2)
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### Page 28

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 this figure.
More DataQtyIdentificationNameTaskStep
(a)(b)--CHANNELClean1
(a)(b)--CUTOUTClean
(a)(b)4-FILLERClean2
(a)(b)4-FASTENER HOLEClean
(c)--CHANNELInspect3
(c)--CUTOUTInspect
(d)4-FILLERInspect4
(d)4-FASTENER HOLEInspect
(a) Remove any dirt, grease, corrosion inhibiting compound, sealant, or other substances from the inspection
area. Refer to SOPM 20-30-03 as an accepted procedure.
(b) Make sure you only use approved compound removal tools. Refer to 737-100/200 AMM 51-31-00 or 737-
300/400/500 AMM 51-31-00 as an accepted procedure.
(c) Do an internal detailed inspection around the channel and around the cutout for any crack and any corro-
sion.
(d) Do an internal detailed inspection of the fillers and around the fastener holes for any crack and any corro-
sion.
FIGURE 1: STRUCTURE COMMON TO THE AFT DRAIN MAST - INTERNAL DETAILED INSPECTION
(SHEET 2 OF 2)
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BOEING SERVICE BULLETIN 737-53A1409
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BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
This Figure applies only to: Group 2.
AFT DRAIN MAST  SKIN CRACK
(TYPICAL)
STA
986.50
S-24L-
S-25L-
FWD
VIEW OF SKIN WITH THE AFT
DRAIN MAST REMOVED
EXTERNAL DETAIL INSPECTION AND  A-A  3023304
EXTERNAL SURFACE HFEC INSPECTION
FIGURE 2: FUSELAGE SKIN COMMON TO THE AFT DRAIN MAST - EXTERNAL DETAILED INSPECTION
AND EXTERNAL SURFACE HIGH FREQUENCY EDDY CURRENT INSPECTION
(SHEET 1 OF 2)
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### Page 30

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 this figure.
More DataQtyIdentificationNameTaskStep
(a)--SKINInspect1
(b)--SKINInspect2
(a) Do an external detailed inspection for any crack and any corrosion around the fastener holes and cutout.
(b) Do an external surface High Frequency Eddy Current (HFEC) inspection on the fuselage skin around the
fastener holes and cutout for any crack in accordance with 737 NDT Manual Part 6, 51-00-00 Procedure
4 or 737 NDT Manual Part 6, 51-00-00 Procedure 23.
FIGURE 2: FUSELAGE SKIN COMMON TO THE AFT DRAIN MAST - EXTERNAL DETAILED INSPECTION
AND EXTERNAL SURFACE HIGH FREQUENCY EDDY CURRENT INSPECTION
(SHEET 2 OF 2)
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BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
This Figure applies only to: Group 2.
FWD
AFT CARGO COMPARTMENT
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS
(SHEET 1 OF 6)
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BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
FWD
INSULATION 9
BOLT LOCATION 1
FWD
BOLT LOCATION 3
BOLT LOCATION 2  • BOLT LOCATION 4
S-24L
BONDING STRAP
9) INSULATION
VIEW OF DRAIN MAST SUPPORT STRUCTURE  3021396
(VIEW LOOKING DOWN)
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS
(SHEET 2 OF 6)
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### Page 33 (OCR)

BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
DRAIN MAST WIRE 6  (57) DRAIN MAST TUBE
6) DRAIN MAST WIRE
BOLT LOCATION 2
BOLT LOCATION 1 B  BOLT  LOCATION 3
BONDING
STRAP
BOLT
LOCATION 4
CHANNEL/FILLER
14 SKIN
DECO
AFT DRAIN MAST  FWD
A-A
FILLER
3) WASHER
CHANNEL  3 SEAL WASHER
SKIN  DRAIN MAST
BOLT LOCATIONS 1, 2 AND 3
3022525
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS
(SHEET 3 OF 6)
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### Page 34

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 this figure.
More DataQtyIdentificationNameTaskStep
(a)--SEALANTApply1
-1-DRAIN MASTInstall (Kept)2
(b)4-BOLTInstall (Kept)3
(b)4-WASHERInstall (Kept)
(b)4-SEAL WASHERInstall (Kept)
(c)--SEALANTApply4
(d)--DRAIN MAST TUBE /
CLAMP
Connect5
-2-DRAIN MAST WIREConnect6
(e)(f)--DRAIN MASTInspect7
(g)--CORROSION INHIBIT-
ING COMPOUND
Apply8
---INSULATIONInstall (Kept)9
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS
(SHEET 4 OF 6)
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More DataQtyIdentificationNameTaskStep
---ACCESS PANELInstall (Kept)10
(a) Apply sealant BMS 5-95, Type 1, Class B-1/2 or Class B-2 to the drain mast and the airplane faying sur-
faces. Make sure you do not damage the skin when you apply the sealant. Refer to SOPM 20-50-19, and
737-100/200 AMM 51-31-00 or 737-300/400/500 AMM 51-31-00 as accepted procedures.
(b) Install drain mast bolts and washers in accordance with Table 1. Make sure that you install the kept
bonding strap at Bolt Location 4 in accordance with Table 1.
(c) Make a fillet seal (aerodynamic smoother) around the drain mast with sealant BMS 5-95, Type 1, Class
B-1/2 or Class B-2. Make sure you do not damage the skin when you apply the sealant. Refer to SOPM
20-50-19, and 737-100/200 AMM 51-31-00 or 737-300/400/500 AMM 51-31-00 as accepted procedures.
(d) Connect the kept drain mast tube to the fitting on the drain mast with the kept clamp.
(e) Do a check for leaks on the drain mast in accordance with the instructions that follow: Plug the drain mast.
Let the water run from the sink of an adjacent lavatory. Check for leaks at the drain mast tube connection
to the drain mast. Remove the plug from the drain mast.
(f) Do a check for heating of the drain mast. Refer to 737-100/200 AMM 30-71-00 or 737-300/400/500 AMM
30-71-00 as accepted procedures.
(g) Apply Corrosion Inhibiting Compound BMS 3-29 to the area where corrosion inhibiting compound was
removed for inspection. Refer to SOPM 20-41-05 as an accepted procedure.
Table 1: Installation of the Drain Mast Bolts, Washers, and Bonding Strap
More DataQTYPART NUMBERNAMEBOLT LOCATION
(a)(b)1BACB30LM4-4BoltBolt Location 1
(b)1NAS1149D0416HWasher
(b)1NAS1523C4RSeal Washer
(a)(b)1BACB30LM4-4BoltBolt Location 2
(b)1NAS1149D0416HWasher
(b)1NAS1523C4RSeal Washer
(a)(b)1BACB30LM4-4BoltBolt Location 3
(b)1NAS1149D0416HWasher
(b)1NAS1523C4RSeal Washer
(a)(b)(c)(d)(e)1BACB30LM4-4BoltBolt Location 4
(b)(c)(d)(e)1NAS1149D0416HWasher
(b)(c)(d)(e)1NAS1523C4RSeal Washer
(b)(c)(d)(e)1Kept PartBonding Strap
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS
(SHEET 5 OF 6)
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Table 1: Installation of the Drain Mast Bolts, Washers, and Bonding Strap
More DataQTYPART NUMBERNAMEBOLT LOCATION
(a) Apply torque to the drain mast bolts in accordance with the instructions that follow: Apply a torque of 8 -
12 inch-pounds to bolt locations 1 and 4. Apply a torque of 8 - 12 inch-pounds to bolt locations 2 and 3.
Apply a torque of 38 - 42 inch-pounds to bolt locations 1 and 4. Apply a torque of 38 - 42 inch-pounds to
bolt locations 2 and 3. Apply a final torque of 78 - 82 inch-pounds to bolt locations 1 and 4. Apply a final
torque of 78 - 82 inch-pounds to bolt locations 2 and 3. Refer to SOPM 20-50-01 as an accepted procedure.
(b) Apply chemical conversion coating Type 2, Class A to the bare surfaces of the washers and bonding strap
lug after you install them. Refer to SOPM 20-43-03 as an accepted procedure. Apply one coat of primer
BMS 10-11, Type I to the drain mast bolts, washers, and bonding strap lug. Refer to SOPM 20-41-02 as
an accepted procedure.
(c) This is the forward drain mast bolt location.
(d) These are electrical bonding parts. Clean the drain mast bolt, the washers, and the bonding strap before
you install them. Refer to SOPM 20-11-03, Cleaning Method CM3, as an accepted procedure. Make sure
the bonding area meets electrical bonding requirements. The resistance between the bonding strap and
the airplane structure must be less than 0.001 ohm. Refer to SWPM 20-20-00 and SWPM 20-20-10 as
accepted procedures.
(e) Apply sealant BMS 5-95, Type 1, Class B-1/2 or B-2 to the drain mast bolt, washers, and bonding strap
lug. This gives corrosion protection at the electrical bonding location. Refer to SOPM 20-50-19, 737-
100/200 AMM 51-31-00 or 737-300/400/500 AMM 51-31-00 as accepted procedures.
FIGURE 3: AFT WASTE WATER DRAIN MAST CLOSE ACCESS
(SHEET 6 OF 6)
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This Appendix applies only to: Group 2.
Logic diagrams are provided as an aid only. Information contained in Paragraph 1.E., Compliance is the primary
source for compliance times. Information contained in Paragraph 3.B., Work Instructions is the primary source
for tasks required for compliance.
1. The table below gives the description for the parts and conditions called out in the logic diagrams.
DescriptionTitle
ANY CRACK OR ANY CORROSION FOUND AS A RESULT OF INTERNAL
DETAILED INSPECTION
CONDITION 1
NO CRACK AND NO CORROSION FOUND AS A RESULT OF INTERNAL
DETAILED INSPECTION
CONDITION 2
ANY CRACK OR ANY CORROSION FOUND AS A RESULT OF EXTERNAL
DETAILED AND HFEC INSPECTION
CONDITION 3
NO CRACK AND NO CORROSION FOUND AS A RESULT OF EXTERNAL
DETAILED AND HFEC INSPECTION
CONDITION 4
2. The table below gives the description for the flag notes called out in the logic diagram.
DescriptionFlag Note Letter
More than one CONDITION can be applicable on each airplane.(a)
APPENDIX A: SKIN AND STRUCTURE COMMON TO THE AFT DRAIN MAST INSPECTION
(SHEET 1 OF 2)
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BOEING SERVICE BULLETIN 737-53A1409
ALERT  ALERT
WHICHEVER OCCURS LATER
WITHIN 2,500 FLIGHT CYCLES
BEFORE 25,000 TOTAL  AFTER THE ORIGINAL ISSUE
FLIGHT CYCLES  DATE OF SERVICE BULLETIN
SB 737-53A1409
ACTION 1: DO PART 2: INTERNAL DETAILED
INSPECTION AROUND THE FASTENER HOLES,
CUTOUT, CHANNEL, AND FILLERS FOR ANY
CRACK AND ANY CORROSION
ACTION 2: DO PART 3: EXTERNAL DETAILED
INSPECTION AND EXTERNAL SURFACE HIGH
FREQUENCY EDDY CURRENT (HFEC)
INSPECTION ON THE FUSELAGE SKIN AROUND
THE FASTENER HOLES AND CUTOUT FOR ANY
CRACK AND ANY CORROSION
CONDITION 1  CONDITION 2  CONDITION 3  CONDITION 4
a)  (a)
12,000 FLIGHT  12,000 FLIGHT
BEFORE FURTHER  CYCLES OR 6  BEFORE FURTHER  CYCLES OR 6
FLIGHT  YEARS,  FLIGHT  YEARS,
WHICHEVER  WHICHEVER
OCCURS FIRST  OCCURS FIRST
REPEAT PART 3:
CONTACT THE  REPEAT PART 2:  CONTACT THE  EXTERNAL
BOEING  INTERNAL  BOEING  DETAILED
COMPANY FOR  DETAILED  COMPANY FOR  INSPECTION AND
REPAIR  INSPECTION  REPAIR  EXTERNAL
INSTRUCTIONS  AROUND THE  INSTRUCTIONS  SURFACE HIGH
AND DO THE  FASTENER HOLES,  AND DO THE  FREQUENCY EDDY
REPAIR  CUTOUT,  REPAIR  CURRENT (HFEC)
CHANNEL, AND  INSPECTION ON
FILLERS FOR ANY  THE FUSELAGE
CRACK AND ANY  SKIN AROUND THE
CORROSION  FASTENER HOLES
AND CUTOUT FOR
ANY CRACK AND
ANY CORROSION
3021397
APPENDIX A: SKIN AND STRUCTURE COMMON TO THE AFT DRAIN MAST INSPECTION
(SHEET 2 OF 2)
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