About AAR Circular Letters
Circular letter summaries are produced monthly by Greenbrier Management Services Group.
AAR circular letters provide information of general applicability to the railroad industry, including proposed and final rules, revisions, standards and recommended practices, and calls for comments. These summaries provide the main points of circular letters issued in the prior month, as well as important implementation deadlines.
For access to the complete circular letter, please go to my.aar.org/circulars. Circular letters are a fee-based service provided by the AAR’s Transportation Technology Center Incorporated (TTCI). You may subscribe online at publications@aar.com or call 719.584.0538.
Implementation Circulars
C-14531
MSRP, Section M, LOCOMOTIVES AND LOCOMOTIVE INTERCHANGE EQUIPMENT: Recommended Practice RP-509 – BRAKING RATIOS FOR LOCOMOTIVES
Issued: April 8, 2025
Effective: April 8, 2025
On February 28, 2025, Circular Letter C-14512 was issued to solicit comments on the proposed revisions with clarifying language to replace the word ‘series‘ with the term ‘locomotive model‘ (along with a definition) within paragraph 2.1. No comments were received. The revised RP-509 is hereby implemented and effective immediately. A copy is attached to this circular for your reference.
The revised RP-509 will be reflected in the next issue of Section M. In the interim, please insert this circular into your copy of MSRP Section M and be governed accordingly.
C-14533
Additions to MSRP F, Sensors, S-6101 –Detector Calibration & Validation Requirements / WILD Validation Standards
Issued: April 10, 2025
Effective: April 10, 2025
On February 26, 2025, AAR’s Equipment Health Monitoring Committee (EHMC) issued a comment circular (C-14511) seeking comments on its proposal to implement two new publications that outline the requirements for instrumentation and measurement of wheel/rail vertical loads and impact loads as a means of quantifying the accuracy and repeatability of wheel impact load detectors systems (WILD). The publications are:
- S-6101B Industry Data Validation: Wheel Impact Load Detector (WILD)
- M-6101 Specification for Instrumented Wheel Sets for Measuring Vertical Impact Loads
EHMC received nine questions from a total of two interested parties. EHMC determined that no technical changes would be needed in response to the questions, but did make two changes for clarity. Modifications will be incorporated in the next issue of the Manual of Standards and Recommended Practices, Section F. Please update your library and be governed accordingly.
C-14534
Circular No. 43-I, Rules Governing the Loading, Blocking, and Bracing of Freight in Closed Containers and Trailers in Intermodal Service (DP&FC)
Issued: April 14, 2025
Effective: April 14, 2025
The AAR’s Damage Prevention & Freight Claim Committee (DP&FC) has approved changes to Circular No. 43-H, Rules Governing the Loading, Blocking, and Bracing of Freight in Closed Trailers and Containers for TOFC/COFC Service. This revision to Circular 43, Rules Governing the Loading, Blocking, and Bracing of Freight in Closed Containers and Trailers in Intermodal Service are now implemented and effective immediately.
C-14536
AAR Manual of Standards and Recommended Practices (MSRP) Section K-VI Railway Data Management and Communications, Standard S-9506.V1.0
Issued: April 15, 2025
Effective: April 15, 2025
S-9506.V1.0 was Adopted in 2024 and Revised in 2025 and is attached to this circular in PDF format. S-9506.V1.0 will be incorporated into the next issue of the MSRP Section K-VI Railway Data Management and Communications. In the interim, please insert the Circular in your copy of the MSRP Section K-VI and be governed accordingly.
C-14538
General Rules 17, 19, 29, 30 and Appendix D – Section 1 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 15, 2025
Effective: April 15, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 1 OTLR manual for General Rules 17, 19, 29, and Appendix D. See Circular for details. The implementation of these revisions is effective immediately and will be included in the next edition of the OTLR manual. In the interim, please insert the circular attachments for General Rules 17, 19, 29, 30 and Appendix D in your Section 1 copy and be governed accordingly.
C-14537
General Rules 1, 6, 11, and 13 – Section 1 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 15, 2025
Effective: April 15, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 1 OTLR manual for General Rules 1, 6, 11, and 13. See Circular for details. The implementation of these revisions is effective immediately and will be included in the next edition of the OTLR manual. In the interim, please insert the circular attachments for General Rules 1, 6, 11, and 13 in your Section 1 copy and be governed accordingly.
C-14540
Steel Pipe Figure 128-B – Section 2 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 16, 2025
Effective: April 16, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 2 OTLR manual for Steel Pipe Figure 128-B. See Circular for details. The implementation of these revisions to Section 2 is effective immediately and will be included in the next edition of the AAR’s OTLR manual. In the interim, please insert the circular attachment for Figure 128-B in your copy of Section 2 and be governed accordingly.
C-14539
Figures 29-L, 29-M, 129, 154-B and 247-A – Section 2 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 16, 2025
Effective: April 16, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 2 OTLR manual for Figures 29-L, 29-M, 129, 154-B and 247-A. See Circular for details. The implementation of these revisions to Section 2 is effective immediately and will be included in the next edition of the AAR’s OTLR manual. In the interim, please insert the circular attachment for Figures 29-L, 29-M, 129, 154-B and 247-A in your copy of Section 2 and be governed accordingly.
C-14551
Additions to MSRP F, Sensors, S-6102 Wayside Passing Data Format – WPD Detector Readings—Extension of Readings
Issued: April 21, 2025
Effective: April 21, 2025
This implementation circular is being released to the industry to advise of modifications to the AAR’s Manual of Standards & Recommended Practices (MSRP) Section F – Sensors / S-6102 Wayside Passing Data Format. On March 13, 2025, AAR’s Equipment Health Monitoring Committee (EHMC) issued a comment circular (C-14518) seeking comments on this change and received none.
Modifications will be incorporated in the next issue of the Manual of Standards and Recommended Practices, Section F. Please update your library and be governed accordingly.
C-14553
Implementation of two new Figures – 728 and 738, Wheelsets on Specially Equipped Flat Rack Container – Section 7 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 22, 2025
Effective: April 22, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved the addition of following two new Figures 728 and 738 to Section 7 OTLR manual. The implementation of these two new Figures to Section 7 is effective immediately and will be included in the next edition of the AAR’s OTLR manual. In the interim, please insert the circular attachment for Figures 728 and 738 in your copy of Section 7 and be governed accordingly.
C-14554
Revisions to Figures 31-A, 54-B and 117 – Section 5 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 22, 2025
Effective: April 22, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 3 OTLR manual for Figures 31-A, 54-B and 117. The implementation of these revisions to Section 5 is effective immediately and will be included in the next edition of the AAR’s OTLR manual. In the interim, please insert the circular attachment for Figures 31-A, 54-B and 117 in your copy of Section 5 and be governed accordingly.
C-14552
Revisions to Figures 55 and 55-A – Section 3 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 22, 2025
Effective: April 22, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 3 OTLR manual for Figures 55 and 55-A. The implementation of these revisions to Section 3 is effective immediately and will be included in the next edition of the AAR’s OTLR manual. In the interim, please insert the circular attachment for Figures 55 and 55-A in your copy of Section 3 and be governed accordingly.
C-14557
MSRP Section N, Specification M-950A, Universal Wide-Body Bi-Level Fully-Enclosed Auto Rack Car
Issued: April 23, 2025
Effective: April 23, 2025
The Specially Equipped Freight Car Committee is implementing revisions to Specification M-950A , 9.5 Stenciling: Stenciling shall be in accord with the MSRP Section C, Standard S-910, latest edition. The revision is editorial to reflect the change from Section L to Section C S-910.
Comments were solicited on March 14, 2025, with Circular Letter C-14522 providing details of the change. The changes to MSRP Section N, Specification M-950A are now implemented and effective immediately and will be incorporated in the next issue of MSRP Section N. In the interim, please insert the circular attachment into your copy of MSRP Section N and be governed accordingly.
C-14556
MSRP Section N, Specification M-950, Universal Wide-Body Tri-Level Fully-Enclosed Auto Rack Car (Low Deck)
Issued: April 23, 2025
Effective: April 23, 2025
The Specially Equipped Freight Car Committee is implementing revisions to Specification M-950, 9.5 Stenciling: Stenciling shall be in accord with the MSRP Section C, Standard S-910, latest edition. The revision is editorial to reflect the change from Section L to Section C S-910.
Comments were solicited on March 14, 2025, with Circular Letter C-14521 providing details of the change. The changes to MSRP Section N, Specification M-950 are now implemented and effective immediately and will be incorporated in the next issue of MSRP Section N. In the interim, please insert the circular attachment into your copy of MSRP Section N and be governed accordingly.
C-14555
MSRP Section N, Specification M-951, Portable Bridge Plates for Multi-Level Auto Rack Cars
Issued: April 23, 2025
Effective: April 23, 2025
The Specially Equipped Freight Car Committee is implementing revisions to Specification M-951, Section 6.0 Markings. Comments were solicited on March 14, 2025, with Circular Letter C-14520 providing details of the change. The changes to MSRP Section N, Specification M-951 are now implemented and effective immediately and will be incorporated in the next issue of MSRP Section N. In the interim, please insert the circular attachment into your copy of MSRP Section N and be governed accordingly.
C-14559
Figure 88-E and Appendix A – Section 6 of the AAR Open Top Loading Rules Manual (OTLR)
Issued: April 24, 2025
Effective: April 24, 2025
The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 6 OTLR manual for Figure 88-E and Appendix A. The implementation of these revisions to Section 6 is effective immediately and will be included in the next edition of the AAR’s OTLR manual. In the interim, please insert the circular attachment for Figure 88-E and Appendix A in your copy of Section 6 and be governed accordingly.
Call for Comment
C-14532
Proposed New and Deleted Braking Curves and Revisions to MSRP, Section M – LOCOMOTIVES AND LOCOMOTIVE INTERCHANGE EQUIPMENT: Standard, S-5018 – DYNAMIC BRAKING CONTROL
Issued: April 8, 2025
Effective: 30 days for comment.
During their March 25-26, 2025, spring meeting, the AAR Locomotive Committee (LC) approved the request to update four (4) of the six (6) braking curve graphs found as Figs. 3.2, 3.3, 3.4 and 3.6 within paragraph 3.5 of Section M, standard S-5018 – DYNAMIC BRAKING CONTROL. The remaining two (2) curve graphs (Fig 3.1 and Fig 3.5) were determined to have no relevant replacement benefit and were deleted from the revised standard.
The revised S-5018 is attached to this circular letter for industry review and comment.
C-14535
MSRP Section H-II, ROLLER BEARING MANUAL, S-736, S-737, S-738, and S-740, Inspection Probe, and Backing Ring Fillet Gauge
Issued: April 15, 2025
Effective: 30 days for comment.
The purpose of this circular letter is to solicit comments for proposed revisions to MSRP Section H-II, ROLLER BEARING MANUAL, S-736, S-737, S-738, and S-740, adding instruction on how to inspect the roller assembly, and cup using the inspection probe, and adding a new gauge for inspecting the backing ring fillet.
The proposed revision to S-736, S-737, S-738, and S-740 does have costs associated with implementation. The costs associated with implementation are below the thresholds prescribed in AAR Standard S-050.
C-14541
DRAFT S.9103.V1.1 Precision Navigation Module Interface Control Document (ICD), in support of AAR’s MSRP – Section K-II Locomotive Electronics and Train Consist System Architecture
Issued: April 17, 2025
Effective: 30 days for comment.
The Railway Electronics Standard Committee (RESC) of the Association of American Railroads (AAR) is publishing DRAFT S.9103.V1.1 Precision Navigation Module Interface Control Document (ICD) for review and comment. This document specifies an industry-standard ICD that defines high precision navigation messages for PNMs on locomotives. This standard applies to all new PNM devices ordered after January 1, 2021.
C-14550
Revisions to Office Manual, Rule 92
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal to revise Office Manual Rule 92.C to align with time limits in Office Manual Rule 112, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14549
Revisions to Field Manual, Rule 36
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the WABL committee to revise Field Manual Rule 36, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14548
Revisions to Field Manual, Rule 59, Pocket Groups
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Equipment Engineering Committee to revise Field Manual Rule 59, to revise pocket group EOC-6B and to add pocket groups EOC-7F and EOC-9F, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14547
Revisions to Field Manual, Rules 47 and 48
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Coupling System and Truck Castings committee to revise Field Manual Rules 47 and 48, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14546
Revisions to Field Manual, Rule 4
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Car Repair Billing committee to revise Field Manual Rule 4, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14545
Revisions to Field Manual, Rule 36.E
Issued: April 18, 2025
Effective: 30 days for comment.
At the September 2024 meeting of the Arbitration and Rules Committee, a proposal as advanced by the WABL Committee to revise Field Manual Rule 36.E, to prioritize reporting of Why Made Codes, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14544
Revisions to Field Manual, Rule 47.E
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Coupling System and Truck Castings committee to revise Field Manual Rule 47, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14543
Revisions to Field Manual, Rule 95.B.5
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal to revise Field Manual Rule 95.B.5, to address multi-level racks with roof sheets that are leaking or impeding clearance, was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14542
Revisions to Field Manual, Rules 19 and 20
Issued: April 18, 2025
Effective: 30 days for comment.
At the April 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Coupling System and Truck Castings committee to revise Field Manual Rules 19 and 20 was reviewed and approved. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14558
Revisions to Office Manual Rule 112
Issued: April 24, 2025
Effective: 30 days for comment.
At the April 2024 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Car Repair Billing Committee to revise Office Manual Rule 112. The entire text of the revision is identified in the circular. In accordance with Rule 123, comments are herein solicited.
C-14560
MSRP K-III – S-9203C AEI Site-to-Host Consist & Wayside Report Format
Issued: April 30, 2025
Effective: 30 days for comment.
The Automatic Equipment Identification Committee (AEIC) is requesting comments on a proposed change to MSRP, Section K-III. S-9203C – AEI Site-to-Host Consist & Wayside Report Format is being proposed as the standalone publication that combines the information currently contained in:
- S-9203A – AEI Site-to-Host Consist Report Format
- S-9203B – AEI Site-to-Host Wayside Report Format
If approved, publications S-9203A and B will be archived and S-9203C will become the governing publication supporting standard S-9203.
Notice of Circulars
CPC-1428
Alteration of AAR Standard for Tank Cars Specification
Issued: April 9, 2025
Effective: April 9, 2025
The AAR Tank Car Committee authorized the inclusion of AAR 211W5 specifications in M-1002: The specification is valid for use immediately. The tables in the TCOC, Umler and TCID are being updated to include this specification.
The revised proposal is included in this circular and is in effect as of the publication date of this circular.
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