# Boeing Alert Service Bulletin 747-25A3588: Revision 1

- Rights: © The Boeing Company. Filed by the FAA in regulations.gov docket FAA-2011-0041; AD 2011-16-06 incorporates this document by reference. Not covered by OpenAirDocs’ CC0 dedication.
- Document: [Boeing Alert Service Bulletin 747-25A3588](https://openairdocs.org/service-documents/boeing/747-25a3588.md)
- Title as filed: U.S. DOT/FAA - Service Bulletin
SB-747-25A3588-01
- Pages: 38
- PDF: https://openairdocs.org/files/sha256/ba/bd/babd69e29f41e6efd59fb4f3da94bf3505531a76d96e0930ddae2783785b0c7a
- Page: https://openairdocs.org/service-documents/boeing/747-25a3588/file/babd69e29f41

## Text

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### Page 1

Commercial 
Airplanes
747
Service Bulletin
ALERT
Number: 747-25A3588
Original Issue: July 19, 2010
Revision 1: April 07, 2011
ATA System: 2551
SUBJECT: EQUIPMENT/FURNISHINGS - Electrical/Electronic Equipment Centers - Main
Equipment Center Drip Shield Repair
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.
9E991ECCN:
BOEING PROPRIETARY, CONFIDENTIAL, AND/OR TRADE SECRET
Copyright © 2010 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Unpublished Work - All Rights Reserved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.
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Table of Contents
Revision Transmittal Sheet ............................................ 5
Summary ...................................................... 7
1. PLANNING INFORMATION ........................................ 1 1
A. Effectivity ............................................... 1 1
1. Airplanes ............................................ 1 1
2. Spares Affected ........................................ 1 4
B. Concurrent Requirements ...................................... 1 4
C. Reason ................................................ 1 4
D. Description .............................................. 1 4
E. Compliance .............................................. 1 5
F. Approval ............................................... 1 5
G. Manpower .............................................. 1 5
H. Weight and Balance Changes .................................... 1 6
I. Electrical Load Data ......................................... 1 7
J. References .............................................. 1 7
1. Existing Data .......................................... 1 7
2. Data supplied with this Service Bulletin ............................ 1 7
3. Installation Drawings Used in the Preparation of this Service Bulletin ............ 1 7
K. Publications Affected ........................................ 1 7
L. Interchangeability and Intermixability of Parts ........................... 1 7
2. MATERIAL INFORMATION ........................................ 1 9
A. Material - Price and Availability ................................... 1 9
B. Industry Support Information .................................... 1 9
C. Parts Necessary For Each Airplane ................................. 2 0
1. Kits/Parts ............................................ 2 0
2. Parts and Materials Supplied by the Operator ........................ 2 0
3. Parts Modified and Reidentified ................................ 2 1
4. Parts Removed and Not Replaced .............................. 2 1
D. Parts Necessary to Change Spares ................................. 2 1
E. Special Tooling - Price and Availability ............................... 2 1
F. Special Tooling Necessary to do this Service Bulletin ....................... 2 1
3. ACCOMPLISHMENT INSTRUCTIONS .................................. 2 3
A. GENERAL INFORMATION ..................................... 2 3
B. WORK INSTRUCTIONS ....................................... 2 3
FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION ................... 2 5
FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD ......................... 2 9
FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION [Group 1, 3] ........... 3 2
FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION ..... 3 6
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Commercial 
Airplanes
747
Service Bulletin
ALERT
Revision Transmittal SheetNumber: 747-25A3588Original Issue: July 19, 2010
Revision 1: April 07, 2011
ATA System: 2551
SUBJECT: EQUIPMENT/FURNISHINGS - Electrical/Electronic Equipment Centers - Main
Equipment Center Drip Shield Repair
This revision includes all pages of the service bulletin.
COMPLIANCE INFORMATION RELATED TO THIS REVISION
No more work is necessary on the airplane(s) changed in accordance with the original issue of this service
bulletin.
REASON FOR REVISION
This revision is sent to remove airplane RT101 and correct the Operator Supplied materials table.
These sections were changed:
1. Paragraph 1.A., Effectivity - removed airplane RT101. RT101 was modified from passenger to freighter
using non-Boeing engineering
2. Paragraph 2.C.2., Parts and Materials Supplied by the Operator - Added BMS 8-2, Type 13, Any Class,
Grade A.
3. Paragraph 2.C.2., Parts and Materials Supplied by the Operator - Changed the acceptable BMS 8-2 grade
from Grade B to Grade A.
4. Figure 3 - Added instructions to apply a fillet of BMS 5-92 around the perimeter of the panel stiffeners.
5. Figure 4 - Changed the outboard limits of the fiberglass cloth from LBL/RBL 60 to 2.00 minimum overlap
past the LBL/RBL 49 seams.
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.
The data given in Information Notice 747-25A3588 R00 IN01 is included in this revision.
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REVISION HISTORY
July 19, 2010Original Issue:
April 07, 2011Revision 1:
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Commercial 
Airplanes
747
Service Bulletin
ALERT
SummaryNumber: 747-25A3588Original Issue: July 19, 2010
Revision 1: April 07, 2011
ATA System: 2551
SUBJECT: EQUIPMENT/FURNISHINGS - Electrical/Electronic Equipment Centers - Main
Equipment Center Drip Shield Repair
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 will reduce the possibility of water penetration into the main equipment center (MEC).
Cracking of the MEC drip shield has allowed water to drip past the MEC drip shield and through the exhaust
plenum into the MEC. Water penetration into the MEC could result in loss of flight critical systems.
An operator experienced a loss of bus control unit (BCU) #1 and generator control units (GCU's) #1 and #2
while the airplane was still on the ground.
Cracking in the MEC drip shield and exhaust plenum have each been identified as part of the leak path into the
MEC. Multiple operators have reported cracked MEC drip shield. These cracks can allow water to penetrate the
MEC drip shield and enter the MEC.
This service bulletin will install a fiberglass reinforcing overcoat as a terminating action.
Boeing Service Related Problem (SRP) 747-SRP-25-0284 is related to this service bulletin.
ACTION (PRR 85901-102RS)
- Install honeycomb stiffening panels
- Install a fiberglass reinforcing overcoat
EFFECTIVITY
747-400F/-400 Airplanes. Refer to Paragraph 1.A.1., Airplanes for the list of affected airplanes.
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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 inspection, change and/or repair given in this service bulletin be done within 24
months after the original issue date of this service bulletin.
INDUSTRY SUPPORT INFORMATION
Boeing warranty remedies are available for airplanes in warranty as of January 14, 2009. Please refer to
Paragraph 2.B., Industry Support Information.
MANPOWER
Group 1, 3:
Elapsed HoursTotal Task HoursAirplanes
12.7520.50Group 1, 3
Group 2:
Elapsed HoursTotal Task HoursAirplanes
9.0016.75Group 2
MATERIAL INFORMATION
Boeing Supplied Kits/Parts.
Refer to Paragraph 2.A., Material - Price and Availability.
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BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
INSTALL HONEYCOMB  000
STIFFENING PANELS
INSTALL A FIBERGLASS
REINFORCING OVERCOAT
STA
460
STA
440
1971240
Original Issue: July 19, 2010
Revision 1: April 07, 2011  747-25A3588
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Commercial 
Airplanes
747
Service Bulletin
ALERT
Number: 747-25A3588
Original Issue: July 19, 2010
Revision 1: April 07, 2011
ATA System: 2551
SUBJECT: EQUIPMENT/FURNISHINGS - Electrical/Electronic Equipment Centers - Main
Equipment Center Drip Shield Repair
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
Refer to Service Bulletin Index Document D6-30300 Part 3 for Airplane Variable Number, Line
Number, and Serial Number data.
This service bulletin is for the airplanes shown below. Refer to PRR 85901-102RS for data about
this change.
DESCRIPTIONCONFIGURATIONGROUP
747-400 Freighter airplanes that have molded stiffening beads on
the MEC drip shield.
-1
747-400 Freighter airplanes that have aluminum stiffeners installed
on the top of the MEC drip shield by SB 747-25A3086 or in production.
-2
747-400 BCF airplanes that have molded stiffening beads on the
MEC drip shield.
-3
Airplane Models:
747-400, 747-400F
GroupVariable Number
2RL401 - RL402
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GroupVariable Number
1RL403
2RL411 - RL418
1RL419 - RL436
1RL451 - RL456
1RL461 - RL462
1RL471 - RL481
1RL491 - RL492
1RL501 - RL502
1RL511 - RL516
1RL521 - RL522
1RL531 - RL534
1RL551
1RL561 - RL568
1RL571 - RL572
1RL576 - RL577
1RL579
1RL581 - RL586
2RL651 - RL654
1RL655
1RL671 - RL675
1RL681 - RL684
1RL751 - RL752
3RM128
2RM851 - RM858
1RM859
2RM861
1RM862 - RM863
2RM871 - RM876
1RM877 - RM880
2RM881 - RM886
1RM887 - RM890
2RM891 - RM899
2RM901 - RM903
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GroupVariable Number
1RM904 - RM906
2RM911
2RR701
2RR721 - RR724
2RR746 - RR748
2RR851 - RR856
2RR861 - RR862
2RR951 - RR952
3RT021 - RT022
3RT031 - RT033
3RT071 - RT072
3RT075
3RT161
3RT164
3RT456
3RT461
3RT501
3RT506 - RT510
3RT513
3RT516
3RT518 - RT520
3RT524
3RT526
3RT528
3RT530
3RT572 - RT579
3RT642
3RT655 - RT657
3RT751 - RT752
3RT781 - RT782
3RT837
3RT967
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2. Spares Affected
None.
B. Concurrent Requirements
None.
C. Reason
This service bulletin will reduce the possibility of water penetration into the main equipment center
(MEC). Cracking of the MEC drip shield has allowed water to drip past the MEC drip shield and through
the exhaust plenum into the MEC. Water penetration into the MEC could result in loss of flight critical
systems.
An operator experienced a loss of bus control unit (BCU) #1 and generator control units (GCU's) #1
and #2 while the airplane was still on the ground.
Cracking in the MEC drip shield and exhaust plenum have each been identified as part of the leak path
into the MEC. Multiple operators have reported cracked MEC drip shield. These cracks can allow water
to penetrate the MEC drip shield and enter the MEC.
This service bulletin will install a fiberglass reinforcing overcoat as a terminating action.
Boeing Service Related Problem (SRP) 747-SRP-25-0284 is related to this service bulletin.
Revision 01 is sent to remove airplane RT101 and correct the Operator Supplied materials table.
D. Description
- Install honeycomb stiffening panels
- Install a fiberglass reinforcing overcoat
Revision 01 - No more work is necessary on airplanes changed in accordance with the original issue
of this service bulletin.
The work in this service bulletin is done in the maintenance zone(s) given below.
Group 1-2:
Affected Maintenance Zones
ZoneModel
117, 118747-400F
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Group 3:
Affected Maintenance Zones
ZoneModel
117, 118747-400
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 inspection, change and/or repair given in this service bulletin be done
within 24 months after the original issue date of this service bulletin.
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
The table below shows an estimate of the task hours necessary to do this change 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 1, 3:
MEC Drip Shield Reinforcing Fiberglass Overcoat
Elapsed HoursTask-HoursNumber of Per-
sons
Task
3.006.002Open Access
1.753.501Figure 1
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Group 1, 3:
MEC Drip Shield Reinforcing Fiberglass Overcoat
Elapsed HoursTask-HoursNumber of Per-
sons
Task
0.50 (a)0.50 (a)1Figure 2
3.753.751Figure 3
1.251.251Figure 4
3.006.002Close Access
12.0019.75Total per airplane
(a) Estimate is per hole to be repaired and is not included in total given.
Operator should multiply number of holes to be repaired by estimate
shown and add to total to arrive at revised total.
Group 2:
MEC Drip Shield Reinforcing Fiberglass Overcoat
Elapsed HoursTask-HoursNumber of Per-
sons
Task
3.006.002Open Access
3.503.501Figure 1
0.50 (a)0.50 (a)1Figure 2
1.251.251Figure 4
3.006.002Close Access
9.0016.75Total per airplane
(a) Estimate is per hole to be repaired and is not included in total given.
Operator should multiply number of holes to be repaired by estimate
shown and add to total to arrive at revised total.
H. Weight and Balance Changes
Group 1, 3:
Change in Moment
(Pound-Inches)
Change in Weight
(Pounds)Airplane
+1485.0+3.3Group 1, 3
Group 2:
Change in Moment
(Pound-Inches)
Change in Weight
(Pounds)Airplane
+1305.0+2.9Group 2
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I. Electrical Load Data
Not changed.
J. References
1. Existing Data
a. Engineering Change Memo PRR 85901-102RS
b. Boeing Service Related Problem (SRP) 747-SRP-25-0284
c. Standard Overhaul Practices Manual (SOPM) 20-30-03, 20-50-12
d. 747-400 Aircraft Maintenance Manual (AMM) 25-00-00, 25-57-01, 25-57-04, 25-57-06,
25-58-01, 25-58-02, 53-21-02
e. 747-400 Structural Repair Manual (SRM) 51-70-06
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:
Chapter-SectionPublication
25-51, 51-41747 Illustrated Parts Catalog
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 does not affect FCS, therefore DTIs are not necessary.
L. Interchangeability and Intermixability of Parts
Refer to Paragraph 2.C., Parts Necessary for Each Airplane, for interchangeability and intermixability
information.
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2.    MATERIAL INFORMATION
A. Material - Price and Availability
Boeing can supply the kits shown in Paragraph 2.C., Parts Necessary for Each Airplane. Operators
are encouraged to share schedule requirements with Boeing for incorporation of the service bulletin.
The kits are subject to the terms and conditions of the Boeing standard purchase order acknowledgment.
Prices are in United States Dollars. Terms: Net 30 days.
Reference this service bulletin and submit your purchase order by one of these methods:
1. Order on-line via ATA Spec 2000 or The Boeing PART Page
2. Fax to (206) 662-7145
Group 1:
REFER TO THE BOEING PART PAGE ON MYBOEINGFLEET.COM OR CONTACT FIRST RESPONDER
AT FR@BOEING.COM FOR THE LATEST REORDER LEAD TIME (ROLT) AND PRICE INFORMATION
Unit Price as of
the original issue
date of this Ser-
vice Bulletin (US
Dollars)
ROLT as of the
original issue
date of this Ser-
vice Bulletin (Cal-
endar Days)
QTYDateNameKit Number
$1,109.0015039October 6,
2010
TOP KIT - MEC DRIP
SHIELD REPAIR
015U1895-1
Group 3:
REFER TO THE BOEING PART PAGE ON MYBOEINGFLEET.COM OR CONTACT FIRST RESPONDER
AT FR@BOEING.COM FOR THE LATEST REORDER LEAD TIME (ROLT) AND PRICE INFORMATION
Unit Price as of
the original issue
date of this Ser-
vice Bulletin (US
Dollars)
ROLT as of the
original issue
date of this Ser-
vice Bulletin (Cal-
endar Days)
QTYDateNameKit Number
$1,109.0015012October 6,
2010
TOP KIT - MEC DRIP
SHIELD REPAIR
015U1896-1
B. Industry Support Information
Boeing warranty remedies are available for 747 airplanes in warranty as of January 14, 2009. For
inspection task hour reimbursement for airplanes in warranty as of that date, send a warranty claim to
Boeing Commercial Airplanes Group - Warranties. If the condition described in this service bulletin is
found during the inspection for airplanes in warranty as of that date and additional task hours and kits
are required, send a warranty claim to Boeing Commercial Airplanes Group - Warranties. Please refer
to this service bulletin number and reference the airplane variable numbers in your purchase order.
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C. Parts Necessary For Each Airplane
1. Kits/Parts
To get the kits/parts shown below, refer to Paragraph 2.A., Material - Price and Availability.
Figure Kit
3Top Kit
1015U1895-1
1015U1896-1
Group 1:
KIT 015U1895-1
NOTES
Existing Part
NumberName
Figure
New Part Number
3
QTY
(a)HONEYCOMB
CORE PANEL
1284U1135-98
(a)HONEYCOMB
CORE PANEL
2284U1135-99
(a) This part not used in production.
Group 3:
KIT 015U1896-1
NOTES
Existing Part
NumberName
Figure
New Part Number
3
QTY
(a)HONEYCOMB
CORE PANEL
1284U1135-98
(a)HONEYCOMB
CORE PANEL
2284U1135-99
(a) This part not used in production.
2. Parts and Materials Supplied by the Operator
NotesNameQTYPart Number /
Specification
(a)ADHESIVE1 QtBMS 5-92, Any
Type
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NotesNameQTYPart Number /
Specification
(a)SEALANT-BMS 5-95, Type I,
Class B
(a)FIBERGLASS SHEET-BMS 8-2, Type 13,
23, 26, or 35, Any
Class, Grade A
(a)EPOXY RESIN1 QtBMS 8-201, Type
III or Type IV
(a)FIBERGLASS CLOTH1 RollBMS 9-3, TYPE H,
H-2, or H-3,
CLASS 7
(b)PHENOLIC MICROBALLOONS1 ozPhenoset Micro-
spheres, No. BJ-
0930
(a) See the Qualified Products List at the end of the Boeing Material Specification (BMS) for
supplier data.
(b) Malayan Adhesives & Chemicals Sdn Bhd, No 9, Jalan Utas 15/7, P. O. BOX 7086, 40702
Shah Alam, Selangor Darul Ehsan, Malaysia. (603) 5566-1188
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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BLANK PAGE

### Page 23

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
5. A General Visual Inspection is defined as: A visual examination of an interior or
exterior area, installation or assembly to detect obvious damage, failure or irregularity.
This level of inspection is made from within touching distance unless otherwise
specified. A mirror may be necessary to enhance visual access to all exposed surfaces
in the inspection area. This level of inspection is made under normally available
lighting conditions such as daylight, hangar lighting, flashlight or drop-light and may
require removal or opening of access panels or doors. Stands, ladders or platforms
may be required to gain proximity to the area being checked.
6. 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.
B. WORK INSTRUCTIONS
1. Remove cargo handling equipment between STA 420 and STA 460 and LBL 55 and RBL 55. Refer
to 747-400 AMM 25-57-01, 747-400 AMM 25-57-04, 747-400 AMM 25-57-06, 747-400 AMM
25-58-01, 747-400 AMM 25-58-02 as an accepted procedure.
2. Remove main deck floor panels between STA 420 and STA 460 and LBL 55 and RBL 55. Refer
to 747-400 AMM 53-21-02 as an accepted procedure.
3. Clean the MEC drip shield and do a general visual inspection for cracks and holes on the top
surface of the MEC drip shield in accordance with Figure 1.
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a. If any crack is found, repair the crack. Refer to 747-400 AMM 25-00-00 as an accepted
procedure.
b. If any hole is found, repair the hole in accordance with Figure 2.
c. Group 1, 3:
If no cracks or holes are found, proceed to Work Instruction 4.
d. Group 2:
If no cracks or holes are found, proceed to Work Instruction 5.
4. Group 1, 3:
Install MEC drip shield panel stiffeners in accordance with Figure 3
5. Install fiberglass reinforcing overcoat to MEC drip shield in accordance with Figure 4.
6. Install main deck floor panels between STA 420 and STA 460 and LBL 55 and RBL 55. Refer to
747-400 AMM 53-21-02 as an accepted procedure.
7. Install cargo handling equipment between STA 420 and STA 460 and LBL 55 and RBL 55. Refer
to 747-400 AMM 25-57-01, 747-400 AMM 25-57-04, 747-400 AMM 25-57-06, 747-400 AMM
25-58-01, 747-400 AMM 25-58-02 as an accepted procedure.
8. Put the airplane back to a serviceable condition.
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BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
STA
440
STA
460
FWD
1971230
FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION
(SHEET 1 OF 4)
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### Page 26

FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION
(SHEET 2 OF 4)
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BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
MEC DRIP
SHIELD GUTTER
CRACK
MULTIPLE
CRACKS
MEC DRIP
SHIELD GUTTER
HOLE
1971626
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.
FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION
(SHEET 3 OF 4)
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### Page 28

MORE DATAQTYIDENTIFICATIONNAMETASKSTEP
Solvent clean, refer
to SOPM 20-30-03
as an accepted pro-
cedure.
--MEC DRIP SHIELDClean1
Carefully remove
any loose old
sealant along BL49
and BL 0 seams and
around any fasten-
ers without causing
further damage to
MEC drip shield.
--SEALANTRemove2
Solvent clean, refer
to SOPM 20-30-03
as an accepted pro-
cedure.
--MEC DRIP SHIELDClean3
Abrasive clean, refer
to SOPM 20-30-03
as an accepted pro-
cedure.
--MEC DRIP SHIELDClean4
Solvent clean, refer
to SOPM 20-30-03
as an accepted pro-
cedure.
--MEC DRIP SHIELDClean5
Apply sealant to
area where old
sealant was re-
moved along BL49
and BL 0 seams and
around any fasten-
ers. Refer to SOPM
20-50-12 as an ac-
cepted procedure.
-BMS 5-95SEALANTApply6
Do a general visual
inspection of the
MEC drip shield sur-
face for cracks or
broken areas.
--MEC DRIP SHIELDInspect7
FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION
(SHEET 4 OF 4)
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BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
STA
440
STA
460
A TYPICAL
1971631
FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD
(SHEET 1 OF 3)
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### Page 30 (OCR)

BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
CRACKS
MEC DRIP
SHIELD GUTTER
- 2.0 (TYPICAL)
AREA TO BE
REMOVED
1971629
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.
FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD
(SHEET 2 OF 3)
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### Page 31

MORE DATAQTYIDENTIFICATIONNAMETASKSTEP
Cut MEC drip shield
to remove material
around broken area.
--MEC DRIP SHIELDCut1
Cut a piece of BMS
8-2 FIBERGLASS
SHEET to cover the
removed section
with a minimum 2.0
inch overlap.
1BMS 8-2FIBERGLASS SHEETCut2
Bond using BMS 5-
92. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
1BMS 8-2FIBERGLASS SHEETBond3
FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD
(SHEET 3 OF 3)
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BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
This Figure applies only to: Group 1, 3.
000
STA
460
STA
440
AND
1971646
FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION
(SHEET 1 OF 4)
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### Page 33 (OCR)

BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
RBL
49
RIGHT SEAM -
LBL
CENTER SEAM  49
LEFT SEAM
LBL
24.5
RBL
23
1971720
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.
FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION
(SHEET 2 OF 4)
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### Page 34

MORE DATAQTYIDENTIFICATIONNAMETASKSTEP
Install fiberglass
strips along seams
at BL 0, LBL 49, and
RBL 49. Fiberglass
cloth should extend
3 inches on either
side of the seams.
Bond using BMS 8-
201 Type III or Type
IV. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
-BMS 9-3, TYPE H, H-2,
OR H-3, CLASS 7
FIBERGLASS CLOTHInstall (New)1
Locate honeycomb
core panel between
molded stiffening
beads as shown.
1284U1135-98HONEYCOMB CORE
PANEL
Locate2
Locate honeycomb
core panel between
molded stiffening
beads as shown.
2284U1135-99HONEYCOMB CORE
PANEL
Locate3
Drill .094 inch holes,
as required, thru
honeycomb core
panel and MEC drip
shield to install
enough clecos to
pull the top surface
of the MEC drip
shield flat.
--HOLEDrill4
Install enough cle-
cos to pull the top
surface flat against
the honeycomb core
panel.
--CLECOInstall (New)
--CLECORemove
FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION
(SHEET 3 OF 4)
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### Page 35

MORE DATAQTYIDENTIFICATIONNAMETASKSTEP
Bond using BMS 5-
92. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
-BMS 5-92ADHESIVEApply5
Bond using BMS 5-
92. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
1284U1135-98HONEYCOMB CORE
PANEL
Install (New)
--CLECOInstall (New)
Optional, a fillet may
be added around the
panel stiffener to re-
duce air bubbles
when fiberglass
cloth is overlaid. (a)
-BMS 5-92ADHESIVEApply
Bond using BMS 5-
92. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
-BMS 5-92ADHESIVEApply6
Bond using BMS 5-
92. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
2284U1135-99HONEYCOMB CORE
PANEL
Install (New)
--CLECOInstall (New)
Optional, a fillet may
be added around the
panel stiffener to re-
duce air bubbles
when fiberglass
cloth is overlaid. (a)
-BMS 5-92ADHESIVEApply
Remove clecos after
panel has cured to
the top surface of
the MEC drip shield.
--CLECORemove7
(a) As an option, phenolic microballoons may be added to BMS 5-92 to increase the viscosity of the adhesive
while building the fillet. Dry the microballoons at 125 to 350 F for 30 minutes +10/-0 minutes, until there
is no more than 0.2 percent weight loss on successive weighing. Blend the A and B components of BMS
5-92 in accordance with SOPM 20-50-12, Type 70, and then add fifteen parts by weight of microballoons
to one hundred parts by weight of blended BMS 5-92 and blend thoroughly.
FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION
(SHEET 4 OF 4)
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BOEING SERVICE BULLETIN 747-25A3588
ALERT  ALERT
000
STA
460
STA
440
1971653
FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION
(SHEET 1 OF 3)
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### Page 37

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)-BMS 9-3, TYPE H, H-2,
OR H-3, CLASS 7
FIBERGLASS CLOTHCut1
(b)-BMS 8-201EPOXY RESINPrepare2
-BMS 9-3, TYPE H, H-2,
OR H-3, CLASS 7
FIBERGLASS CLOTHInstall (New)3
Bond using BMS 8-
201 Type III or Type
IV. Refer to 747-400
SRM 51-70-06 as an
accepted procedure.
-BMS 8-201EPOXY RESINApply
FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION
(SHEET 2 OF 3)
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MORE DATAQTYIDENTIFICATIONNAMETASKSTEP
(a) Cut fiberglass cloth to overlay the MEC drip shield, in sections as required. Two plies will be required.
Cloth shall extend over sides to within 0.25 inch of bottom of the MEC drip shield. Cloth shall extend a
minimum of 2" outboard of the LBL/RBL 49 seams. All seams shall overlap 2 inch minimum, including
sheet-to-sheet and sheet-to-beam.
(b) Prepare epoxy laminating resin in sufficient quantity. Work in small batches consistent with working life
of resin. Apply mixed resin and cloth using squeegee or similar tool.
FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION
(SHEET 3 OF 3)
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