Boeing Alert Requirements Bulletin 747-28A2373 RB: No revision named, text

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Commercial Airplanes 747 Requirements Bulletin ALERT Number: 747-28A2373 RB Original Issue: November 06, 2025 ATA System: 2817 SUBJECT: FUEL - Horizontal Stabilizer Tank Fuel Transfer System - Transfer Pump Housing Inlet Check Valve and Transfer Pump Motor Impeller Inlet Adapter Inspection and Replacement 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:

Copyright © 2025 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: November 06, 2025 747-28A2373 RB 1 of 29

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Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 2 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Table of Contents

1. EFFECTIVITY5

A. Airplanes5

B. Spares Affected7

2. CONCURRENT REQUIREMENTS7

3. COMPLIANCE7

4. APPROVAL12

5. ACCOMPLISHMENT INSTRUCTIONS13

A. General Information13

B. Work Instructions14

FIGURE 1: HORIZONTAL STABILIZER FUEL TANK - LEFT TRANSFER PUMP HOUSING - INLET CHECK

VALVE (ICV) INSPECTION [Group 1, Configuration 1]19

FIGURE 2: HORIZONTAL STABILIZER FUEL TANK - RIGHT TRANSFER PUMP HOUSING - INLET

CHECK VALVE (ICV) INSPECTION [Group 1, Configuration 1]23

FIGURE 7: HORIZONTAL STABILIZER FUEL TANK - TRANSFER PUMP - MOTOR IMPELLER INLET

ADAPTER (IA) INSPECTION [Group 1, Configuration 1]27

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 3 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 4 of 29 REQUIREMENTS BULLETIN 747-28A2373

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THIS DOCUMENT IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN 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.

THIS IS AN ENHANCED REQUIRED FOR COMPLIANCE DOCUMENT. THE BOEING PROCESSES USED

TO CREATE THE SERVICE BULLETIN (SB) AND THE REQUIREMENTS BULLETIN (RB) ENSURE THAT THE INFORMATION BETWEEN "RC START" AND "RC END" IN THE SB ARE IDENTICAL TO THE INFORMATION IN THE SAME SECTIONS (COMPLIANCE, WORK INSTRUCTIONS…) OF THE RB WHICH THE SB REFERS TO AS THE RELATED DOCUMENT.

1. Effectivity A. Airplanes This bulletin is applicable to 747-8, 747-400 Airplane(s), line number(s) 696, 700, 705, 708, 715, 717, 721-723, 725-749, 751, 753-771, 773-775, 777-809, 811-813, 815-817, 819-821, 823-843, 845-877, 880-885, 887-890, 892-906, 908-913, 915-919, 921-926, 928-934, 936-940, 942-947, 949-951, 953-962, 964-967, 969-971, 973-974, 976-977, 979-990, 992-995, 997-1001, 1003-1007, 1009-1019, 1021-1035, 1037-1041, 1043, 1045-1051, 1053-1059, 1061-1063, 1067-1068, 1070-1086, 1088-1093, 1095, 1097-1104, 1106-1122, 1124, 1126-1138, 1140-1162, 1164, 1166-1168, 1170-1172, 1174-1178, 1180-1183, 1185-1188, 1190-1191, 1193-1202, 1204-1209, 1211-1212, 1214-1216, 1218-1219, 1221, 1223, 1225-1226, 1228-1230, 1232-1234, 1236-1237, 1239, 1241, 1243, 1245, 1247, 1250, 1253, 1258, 1261-1262, 1264-1266, 1268, 1270, 1272-1278, 1280, 1284, 1287, 1289-1290, 1292-1293, 1296-1297, 1299, 1301-1303, 1308, 1313, 1320-1321, 1324-1325, 1327, 1330-1331, 1335-1337, 1343, 1353-1354, 1357-1358, 1434-1435, 1439-1440, 1443, 1446, 1449, 1451, 1453, 1456, 1459, 1466, 1468, 1470, 1472, 1475, 1477, 1480, 1492, 1494-1495, 1497-1500, 1503, 1506-1515, 1517-1518, 1524-1525, 1527, 1529, 1531, 1537-1539 in 1 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.

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 5 of 29

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NOTE: A horizontal stabilizer tank is considered to be "activated" if it has not been deactivated in production or deactivated by an approved alteration.

DESCRIPTIONCONFIGURATIONGROUP 747-400 and 747-8 airplanes.-1 747-400 and 747-8 airplanes equipped with activated Horizontal Stabilizer Fuel Tank with Crane Aerospace Hydro-Aire horizontal stabilizer fuel Transfer Pump Housings and Transfer Pump Motor Impellers.

1 747-400 and 747-8 airplanes not equipped with activated Horizontal Stabilizer Fuel Tank with Crane Aerospace Hydro-Aire horizontal stabilizer fuel Transfer Pump Housings and Transfer Pump Motor Impellers.

2 Airplane Models:

747-400, 747-8 GroupVariable Number 1RC001 - RC009 1RC021 - RC040 1RC051 - RC060 1RC066 - RC072 1RF001 - RF006 1RM001 - RM007 1RM010 - RM013 1RM021 - RM024 1RM026 - RM030 1RM036 - RM045 1RM051 - RM053 1RM071 1RM081 - RM084 1RM091 1RM096 - RM097 1RM116 - RM117 1RM126 - RM132 1RM136 - RM147 GroupVariable Number 1RM156 - RM158 1RM166 - RM177 1RM191 - RM192 1RM231 - RM233 1RM241 - RM246 1RM261 - RM264 1RM316 - RM318 1RM331 - RM333 1RM341 1RM351 - RM355 1RM366 - RM367 1RM401 - RM403 1RM426 1RM431 1RM441 - RM443 1RM445 1RM801 - RM803 1RM811 - RM813 GroupVariable Number 1RT001 - RT014 1RT021 - RT022 1RT031 - RT035 1RT041 - RT047 1RT061 1RT071 - RT075 1RT101 - RT103 1RT121 1RT131 - RT137 1RT151 - RT152 1RT161 - RT168 1RT401 - RT412 1RT431 - RT447 1RT451 - RT469 1RT471 - RT499 1RT501 - RT535 1RT551 - RT568 1RT571 - RT591 Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 6 of 29 REQUIREMENTS BULLETIN 747-28A2373

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GroupVariable Number 1RT601 - RT657 1RT671 - RT673 1RT681 - RT682 1RT691 - RT699 1RT701 - RT704 1RT711 - RT717 1RT741 - RT757 1RT776 - RT777 1RT781 - RT784 GroupVariable Number 1RT801 - RT803 1RT811 - RT814 1RT831 - RT837 1RT861 - RT864 1RT876 - RT880 1RT931 - RT932 1RT945 - RT949 1RT951 - RT955 1RT966 - RT967 GroupVariable Number 1RU001 - RU006 1RU016 - RU017 1RU031 - RU032 1RU051 - RU052 1RU059 - RU062 1RU081 - RU083 1RU101 - RU102 1RU121 - RU132 1RU809 B. Spares Affected None.

2. CONCURRENT REQUIREMENTS None.

3. COMPLIANCE The Federal Aviation Administration (FAA) will possibly release an Airworthiness Directive related to Requirements Bulletin 747-28A2373 RB. The Airworthiness Directive will make the compliance tasks and times given in Requirements Bulletin 747-28A2373 RB mandatory.

Accomplish the required action(s), based on the applicable condition(s) in Table 1 and Table 2, in accordance with Accomplishment Instructions.

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, Configuration 2:

No action required.

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 7 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Group 1, Configuration 1:

Table 1: Left Transfer Pump Housing Inlet Check Valve (ICV) and Transfer Pump Motor Impeller Inlet Adapter (IA) Detailed Inspection Repeat Interval (Not to Exceed) Boeing Recommended Compliance Time ActionCondition -Within 20,000 flight hours after the Original Issue date of Requirements Bulletin 747-28A2373 RB.

ACTION 1: Do a Detailed Inspection (DET) of the left Transfer Pump Housing Inlet Check Valve (ICV) for any damage. (a) All Airplanes.

-Whichever occurs first;ACTION 2: Do a DET of the left Transfer Pump Motor Impeller Inlet Adapter (IA) for any damage. (c)

1. Within 5,000 flight hours after the Original Issue date of Requirements Bulletin 747- 28A2373 RB.

2. Within 1 year after the Original Issue date of Requirements Bulletin 747-28A2373 RB.

20,000 flight hours.-Repeat the DET of the left Transfer Pump Housing ICV for any damage.

(a) CONDITION 1: NO DAM-

AGE FOUND IN THE LEFT

TRANSFER PUMP HOUSING ICV.

-Before further flight.OPTION 1 (ACTION 1):

Replace the left Transfer Pump Housing ICV with a new or serviceable Transfer Pump Housing ICV. (b) CONDITION 2: ANY DAM-

AGE FOUND IN THE LEFT

TRANSFER PUMP HOUSING ICV.

20,000 flight hours.-OPTION 1 (ACTION 2):

Repeat the DET of the left Transfer Pump Housing ICV for any damage.

(a) -Before further flight.OPTION 2 (ACTION 1):

Replace the left Transfer Pump Housing with a Transfer Pump Housing containing a new or serviceable transfer pump housing ICV. (b) 20,000 flight hours.-OPTION 2 (ACTION 2):

Repeat the DET of the left Transfer Pump Housing ICV for any damage.

(a) Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 8 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Group 1, Configuration 1:

Table 1: Left Transfer Pump Housing Inlet Check Valve (ICV) and Transfer Pump Motor Impeller Inlet Adapter (IA) Detailed Inspection Repeat Interval (Not to Exceed) Boeing Recommended Compliance Time ActionCondition 20,000 flight hours.-Repeat the DET of the left Transfer Pump Motor Impeller IA for any damage. (c) CONDITION 3: NO DAM-

AGE FOUND IN THE LEFT

TRANSFER PUMP MO- TOR IMPELLER IA.

-Before further flight.CONDITION 4 (ACTION

1): Replace the left Transfer Pump Motor Impeller with a new or serviceable Transfer Pump Motor Impeller. (d) CONDITION 4: ANY DAM-

AGE FOUND IN THE LEFT

TRANSFER PUMP MO- TOR IMPELLER IA.

20,000 flight hours.-CONDITION 4 (ACTION

2): Repeat the DET of the left Transfer Pump Motor Impeller IA for any damage. (c)

(a) Damage is defined as an ICV for which the hinge pin protrudes past the flapper arm on only one side or there is any metal disk gouging, missing material, corrosion, burrs or raised material found.

(b) A serviceable Transfer Pump Housing ICV is an ICV for which the hinge pin protrudes past the flapper arm on both sides and there is no metal disk gouging, missing material, corrosion, burrs, or raised material.

(c) Damage is defined as a transfer pump motor impeller IA where the Stellite 6 thermal spray coating is scratched or worn to base metal or there is deformation or wear on the inner diameter or outer rim from contact with the inlet check valve.

(d) A serviceable Transfer Pump Motor Impeller is a transfer pump motor impeller that has a transfer pump motor impeller IA where the Stellite 6 thermal spray coating is not scratched or worn to base metal, and there is no deformation or wear on the inner diameter or outer rim from contact with the inlet check valve.

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 9 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Group 1, Configuration 1:

Table 2: Right Transfer Pump Housing Inlet Check Valve (ICV) and Transfer Pump Motor Impeller Inlet Adapter (IA) Detailed Inspection Repeat Interval (Not to Exceed) Boeing Recommended Compliance Time ActionCondition -Within 20,000 flight hours after the Original Issue date of Requirements Bulletin 747-28A2373 RB.

ACTION 1: Do a Detailed Inspection (DET) of the right Transfer Pump Housing Inlet Check Valve (ICV) for any damage. (a) All Airplanes.

-Whichever occurs first;ACTION 2: Do a DET of the right Transfer Pump Motor Impeller Inlet Adapter (IA) for any damage. (c)

1. Within 5,000 flight hours after the Original Issue date of Requirements Bulletin 747- 28A2373 RB.

2. Within 1 year after the Original Issue date of Requirements Bulletin 747-28A2373 RB.

20,000 flight hours.-Repeat the DET of the right Transfer Pump Housing ICV for any damage. (a) CONDITION 5: NO DAM-

AGE FOUND IN THE

RIGHT TRANSFER PUMP HOUSING ICV.

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 10 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Group 1, Configuration 1:

Replace the right Transfer Pump Housing ICV with a new or serviceable Transfer Pump Housing ICV. (b) CONDITION 6: ANY DAM-

AGE FOUND IN THE

RIGHT TRANSFER PUMP HOUSING ICV.

20,000 flight hours.-OPTION 1 (ACTION 2):

Repeat the DET of the right Transfer Pump Housing ICV for any damage. (a) -Before further flight.OPTION 2 (ACTION 1):

Replace the right Transfer Pump Housing with a Transfer Pump Housing containing a new or serviceable transfer pump housing ICV. (b) 20,000 flight hours.-OPTION 2 (ACTION 2):

Repeat the DET of the right Transfer Pump Housing ICV for any damage. (a) 20,000 flight hours.-Repeat the DET of the right Transfer Pump Motor Impeller IA for any damage. (c) CONDITION 7: NO DAM-

AGE FOUND IN THE

RIGHT TRANSFER PUMP MOTOR IMPELLER IA.

-Before further flight.CONDITION 8 (ACTION

1): Replace the right Transfer Pump Motor Impeller with a new or serviceable Transfer Pump Motor Impeller. (d) CONDITION 8: ANY DAM-

AGE FOUND IN THE

RIGHT TRANSFER PUMP MOTOR IMPELLER IA.

20,000 flight hours.-CONDITION 8 (ACTION

2): Repeat the DET of the right Transfer Pump Motor Impeller IA for any damage. (c)

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 11 of 29 REQUIREMENTS BULLETIN 747-28A2373

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Group 1, Configuration 1:

4. APPROVAL This Requirements Bulletin was examined by the Federal Aviation Administration (FAA). The changes specified in this document comply with the applicable regulations and are FAA approved, as well as European Union Aviation Safety Agency (EASA) approved for all EASA approved airplanes listed in this Requirements Bulletin effectivity. This document and its approval were based on the airplane in its original Boeing delivery configuration or as modified by other Boeing changes.

If an airplane has a non-Boeing modification or repair that affects a component or system also affected by this Requirements Bulletin, the operator is responsible for obtaining appropriate regulatory agency approval before incorporating this Requirements Bulletin.

Export Controlled ECCN: 9E991 See page 1 for details Original Issue: November 06, 2025 747-28A2373 RB 12 of 29 REQUIREMENTS BULLETIN 747-28A2373

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