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.

ECCN: 9E991

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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Unpublished Work - All Rights Reserved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,

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4.0
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BOEING SERVICE BULLETIN 747-25A3588

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BLANK PAGE
Table of Contents

Revision Transmittal Sheet ............................................ 5

Summary ...................................................... 7

1. PLANNING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

A. Effectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1. Airplanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2. Spares Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

B. Concurrent Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

C. Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

D. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

E. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

F. Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

G. Manpower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

H. Weight and Balance Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

I. Electrical Load Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

J. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1. Existing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2. Data supplied with this Service Bulletin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3. Installation Drawings Used in the Preparation of this Service Bulletin . . . . . . . . . . . . 17

K. Publications Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

L. Interchangeability and Intermixability of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2. MATERIAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A. Material - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

B. Industry Support Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

C. Parts Necessary For Each Airplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

1. Kits/Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2. Parts and Materials Supplied by the Operator . . . . . . . . . . . . . . . . . . . . . . . . 20

3. Parts Modified and Reidentified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4. Parts Removed and Not Replaced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

D. Parts Necessary to Change Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

E. Special Tooling - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

F. Special Tooling Necessary to do this Service Bulletin . . . . . . . . . . . . . . . . . . . . . . . 21

3. ACCOMPLISHMENT INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

A. GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

B. WORK INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION . . . . . . . . . . . . . . . . . . . 25

FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD . . . . . . . . . . . . . . . . . . . . . . . . . 29

FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION [Group 1, 3] . . . . . . . . . . . 32

FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION . . . . . 36

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BLANK PAGE
Commercial 

Airplanes 747

Service Bulletin

ALERT

Revision Transmittal Sheet 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 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

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
Commercial 

Airplanes 747

Service Bulletin

ALERT

Summary 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.

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:

Airplanes Total Task Hours Elapsed Hours

Group 1, 3 20.50 12.75

Group 2:

Airplanes Total Task Hours Elapsed Hours

Group 2 16.75 9.00

MATERIAL INFORMATION

Boeing Supplied Kits/Parts.

Refer to Paragraph 2.A., Material - Price and Availability.

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BLANK PAGE
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.

GROUP CONFIGURATION DESCRIPTION

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

Variable Number Group

RL401 - RL402 2

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Variable Number Group

RL403 1

RL411 - RL418 2

RL419 - RL436 1

RL451 - RL456 1

RL461 - RL462 1

RL471 - RL481 1

RL491 - RL492 1

RL501 - RL502 1

RL511 - RL516 1

RL521 - RL522 1

RL531 - RL534 1

RL551 1

RL561 - RL568 1

RL571 - RL572 1

RL576 - RL577 1

RL579 1

RL581 - RL586 1

RL651 - RL654 2

RL655 1

RL671 - RL675 1

RL681 - RL684 1

RL751 - RL752 1

RM128 3

RM851 - RM858 2

RM859 1

RM861 2

RM862 - RM863 1

RM871 - RM876 2

RM877 - RM880 1

RM881 - RM886 2

RM887 - RM890 1

RM891 - RM899 2

RM901 - RM903 2

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ALERT ALERT
Variable Number Group

RM904 - RM906 1

RM911 2

RR701 2

RR721 - RR724 2

RR746 - RR748 2

RR851 - RR856 2

RR861 - RR862 2

RR951 - RR952 2

RT021 - RT022 3

RT031 - RT033 3

RT071 - RT072 3

RT075 3

RT161 3

RT164 3

RT456 3

RT461 3

RT501 3

RT506 - RT510 3

RT513 3

RT516 3

RT518 - RT520 3

RT524 3

RT526 3

RT528 3

RT530 3

RT572 - RT579 3

RT642 3

RT655 - RT657 3

RT751 - RT752 3

RT781 - RT782 3

RT837 3

RT967 3

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
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

Model Zone

747-400F 117, 118

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
Group 3:

Affected Maintenance Zones

Model Zone

747-400 117, 118

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

Number of Per- Task-Hours Elapsed Hours

sons

Task

Open Access 2 6.00 3.00

Figure 1 1 3.50 1.75

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
Group 1, 3:

MEC Drip Shield Reinforcing Fiberglass Overcoat

Number of Per- Task-Hours Elapsed Hours

sons

Task

Figure 2 1 0.50 (a) 0.50 (a)

Figure 3 1 3.75 3.75

Figure 4 1 1.25 1.25

Close Access 2 6.00 3.00

Total per airplane 19.75 12.00

(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

Number of Per- Task-Hours Elapsed Hours

sons

Task

Open Access 2 6.00 3.00

Figure 1 1 3.50 3.50

Figure 2 1 0.50 (a) 0.50 (a)

Figure 4 1 1.25 1.25

Close Access 2 6.00 3.00

Total per airplane 16.75 9.00

(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

Airplane (Pounds)

Group 1, 3 +3.3 +1485.0

Group 2:

Change in Moment

(Pound-Inches)

Change in Weight

Airplane (Pounds)

Group 2 +2.9 +1305.0

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
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:

Publication Chapter-Section

747 Illustrated Parts Catalog 25-51, 51-41

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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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT

BLANK PAGE
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 Service Bulletin (US

Dollars)

ROLT as of the

original issue

date of this Service Bulletin (Calendar Days)

Kit Number Name Date QTY

October 6, 39 150 $1,109.00

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 Service Bulletin (US

Dollars)

ROLT as of the

original issue

date of this Service Bulletin (Calendar Days)

Kit Number Name Date QTY

October 6, 12 150 $1,109.00

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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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
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

Top Kit 3

015U1895-1 1

015U1896-1 1

Group 1:

KIT 015U1895-1

NOTES

Existing Part

Name Number

Figure

New Part Number

3

QTY

HONEYCOMB (a)

CORE PANEL

284U1135-98 1

HONEYCOMB (a)

CORE PANEL

284U1135-99 2

(a) This part not used in production.

Group 3:

KIT 015U1896-1

NOTES

Existing Part

Name Number

Figure

New Part Number

3

QTY

HONEYCOMB (a)

CORE PANEL

284U1135-98 1

HONEYCOMB (a)

CORE PANEL

284U1135-99 2

(a) This part not used in production.

2. Parts and Materials Supplied by the Operator

Part Number / QTY Name Notes

Specification

BMS 5-92, Any 1 Qt ADHESIVE (a)

Type

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Part Number / QTY Name Notes

Specification

BMS 5-95, Type I, - SEALANT (a)

Class B

BMS 8-2, Type 13, - FIBERGLASS SHEET (a)

23, 26, or 35, Any

Class, Grade A

BMS 8-201, Type 1 Qt EPOXY RESIN (a)

III or Type IV

BMS 9-3, TYPE H, 1 Roll FIBERGLASS CLOTH (a)

H-2, or H-3,

CLASS 7

Phenoset Micro- 1 oz PHENOLIC MICROBALLOONS (b)

spheres, No. BJ0930

(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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BOEING SERVICE BULLETIN 747-25A3588

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

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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FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION

(SHEET 1 OF 4)

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FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION

(SHEET 2 OF 4)

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ALERT ALERT
The step numbers shown below agree with the numbers shown in the circle symbols in the figure. The QTY

numbers shown below are the number of parts necessary for this figure.

FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION

(SHEET 3 OF 4)

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STEP TASK NAME IDENTIFICATION QTY MORE DATA

Solvent clean, refer

to SOPM 20-30-03

as an accepted procedure.

1 Clean MEC DRIP SHIELD - -

Carefully remove

any loose old

sealant along BL49

and BL 0 seams and

around any fasteners without causing

further damage to

MEC drip shield.

2 Remove SEALANT - -

Solvent clean, refer

to SOPM 20-30-03

as an accepted procedure.

3 Clean MEC DRIP SHIELD - -

Abrasive clean, refer

to SOPM 20-30-03

as an accepted procedure.

4 Clean MEC DRIP SHIELD - -

Solvent clean, refer

to SOPM 20-30-03

as an accepted procedure.

5 Clean MEC DRIP SHIELD - -

Apply sealant to

area where old

sealant was removed along BL49

and BL 0 seams and

around any fasteners. Refer to SOPM

20-50-12 as an accepted procedure.

6 Apply SEALANT BMS 5-95 -

Do a general visual

inspection of the

MEC drip shield surface for cracks or

broken areas.

7 Inspect MEC DRIP SHIELD - -

FIGURE 1: MEC DRIP SHIELD CLEANING AND PREPARATION

(SHEET 4 OF 4)

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FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD

(SHEET 1 OF 3)

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
The step numbers shown below agree with the numbers shown in the circle symbols in the figure. The QTY

numbers shown below are the number of parts necessary for this figure.

FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD

(SHEET 2 OF 3)

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STEP TASK NAME IDENTIFICATION QTY MORE DATA

Cut MEC drip shield

to remove material

around broken area.

1 Cut MEC DRIP SHIELD - -

Cut a piece of BMS

8-2 FIBERGLASS

SHEET to cover the

removed section

with a minimum 2.0

inch overlap.

2 Cut FIBERGLASS SHEET BMS 8-2 1

Bond using BMS 5-

92. Refer to 747-400

SRM 51-70-06 as an

accepted procedure.

3 Bond FIBERGLASS SHEET BMS 8-2 1

FIGURE 2: REPAIR OF HOLES IN MEC DRIP SHIELD

(SHEET 3 OF 3)

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This Figure applies only to: Group 1, 3.

FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION

(SHEET 1 OF 4)

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BOEING SERVICE BULLETIN 747-25A3588

ALERT ALERT
The step numbers shown below agree with the numbers shown in the circle symbols in the figure. The QTY

numbers shown below are the number of parts necessary for this figure.

FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION

(SHEET 2 OF 4)

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ALERT ALERT
STEP TASK NAME IDENTIFICATION QTY MORE DATA

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

1 Install (New) FIBERGLASS CLOTH

Locate honeycomb

core panel between

molded stiffening

beads as shown.

HONEYCOMB CORE 284U1135-98 1

PANEL

2 Locate

Locate honeycomb

core panel between

molded stiffening

beads as shown.

HONEYCOMB CORE 284U1135-99 2

PANEL

3 Locate

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.

4 Drill HOLE - -

Install enough clecos to pull the top

surface flat against

the honeycomb core

panel.

Install (New) CLECO - -

Remove CLECO - -

FIGURE 3: MEC DRIP SHIELD PANEL STIFFENER INSTALLATION

(SHEET 3 OF 4)

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ALERT ALERT
STEP TASK NAME IDENTIFICATION QTY MORE DATA

Bond using BMS 5-

92. Refer to 747-400

SRM 51-70-06 as an

accepted procedure.

5 Apply ADHESIVE BMS 5-92 -

Bond using BMS 5-

92. Refer to 747-400

SRM 51-70-06 as an

accepted procedure.

HONEYCOMB CORE 284U1135-98 1

PANEL

Install (New)

Install (New) CLECO - -

Optional, a fillet may

be added around the

panel stiffener to reduce air bubbles

when fiberglass

cloth is overlaid. (a)

Apply ADHESIVE BMS 5-92 -

Bond using BMS 5-

92. Refer to 747-400

SRM 51-70-06 as an

accepted procedure.

6 Apply ADHESIVE BMS 5-92 -

Bond using BMS 5-

92. Refer to 747-400

SRM 51-70-06 as an

accepted procedure.

HONEYCOMB CORE 284U1135-99 2

PANEL

Install (New)

Install (New) CLECO - -

Optional, a fillet may

be added around the

panel stiffener to reduce air bubbles

when fiberglass

cloth is overlaid. (a)

Apply ADHESIVE BMS 5-92 -

Remove clecos after

panel has cured to

the top surface of

the MEC drip shield.

7 Remove CLECO - -

(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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ALERT ALERT
FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION

(SHEET 1 OF 3)

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ALERT ALERT
The step numbers shown below agree with the numbers shown in the circle symbols in the figure. The QTY

numbers shown below are the number of parts necessary for this figure.

STEP TASK NAME IDENTIFICATION QTY MORE DATA

BMS 9-3, TYPE H, H-2, - (a)

OR H-3, CLASS 7

1 Cut FIBERGLASS CLOTH

2 Prepare EPOXY RESIN BMS 8-201 - (b)

BMS 9-3, TYPE H, H-2, -

OR H-3, CLASS 7

3 Install (New) FIBERGLASS CLOTH

Bond using BMS 8-

201 Type III or Type

IV. Refer to 747-400

SRM 51-70-06 as an

accepted procedure.

Apply EPOXY RESIN BMS 8-201 -

FIGURE 4: MEC DRIP SHIELD FIBERGLASS REINFORCING OVERCOAT INSTALLATION

(SHEET 2 OF 3)

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ALERT ALERT
STEP TASK NAME IDENTIFICATION QTY MORE DATA

(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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ALERT ALERT