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-14718
Subject: Implementation of Revisions to MSRP Section B FREIGHT CAR DRAFT COMPONENTS, New Standard S-122 Cushion Unit Shaft Retainer
Summary: This circular letter notifies the industry of revisions to MSRP Section B FREIGHT CAR DRAFT COMPONENTS, introducing the new Standard S-122 Cushion Unit Shaft Retainer which sets forth geometry and tolerances for interchangeability. The revised Standard S-122 is now implemented and effective immediately, and will be incorporated in the next issue of the Manual of Standards and Recommended Practices, Section B.
Date: 01-05-2026
Effective Date: 01-05-2026
C-14720
Subject: Corrections to the Office Manual Price Matrix Effective January 1, 2026, Replacement Price Master, Rules 5 & 12
Summary: This circular letter addresses corrections to the Office Manual Price Matrix related to job codes connected with recently updated Rules 5 & 12. It includes a replacement Price Master with corrections to material pricing and job code couplets, which will be distributed via a new DAT file in the Railinc CRB application, and provides attached corrected pages for the Office Manual Price Matrix.
Date: 01-08-2026
Effective Date: 01-01-2026
C-14721
Subject: Implementation of Revisions to Steel Beam Figures 106-C and 109 – Section 2 of the AAR Open Top Loading Rules Manual (OTLR)
Summary: The AAR’s Open Top Loading Rules Committee (OTLRC) has approved revisions to Section 2 of the OTLR manual for Steel Beam Figures 106-C and 109, including changes to beam lengths, replacement of sketches, and added notes for load limits and support requirements. These revisions are effective immediately and will be included in the next edition of the OTLR manual, with circular attachments provided for reference.
Date: 01-08-2026
Effective Date: 01-08-2026
C-14723
Subject: Notice to Mechanical Inspection Department (MID) M-1003 Certified Facility Regarding Implementation of Adverse Audit Finding Report Online Tool
Summary: The AAR is implementing the Adverse Audit Finding Report (AAFR) online tool for M-1003 facilities Certified by the Mechanical Inspection Department (MID) Audit Agency. This tool replaces the AAFR paper and email communication processes and will be mandatory for MID audits performed after February 9, 2026. The circular also mentions an attached user guide for the online system.
Date: 01-13-2026
Effective Date: 01-13-2026
C-14726
Subject: Additional Corrections to the Office Manual and Price Matrix & Field Manual Effective January 1, 2026, Rules 4, 8, 16, 17, & 112
Summary: This AAR Circular Letter supplements and supersedes AAR Circular Letter C-14720 issued on January 8, 2026, addressing incorrect information found in relation to Rules 4, 8, 16, 17, & 112 after the release of the January 1, 2026 Office Manual and Price Matrix & Field Manual publications. It includes corrected pages for the AAR Office Manual and Price Matrix & Field Manual publications, which are mandatory and must be maintained until the next revision of the manuals.
Date: 01-27-2026
Effective Date: 01-27-2026
C-14727
Subject: Implementation Circular: Modifications to MSRP F, Sensors, S-920 AAR Component Identification (CID) Bar Code Standard – Appendix A – Axle Element C307
Summary: This implementation circular advises the industry of modifications to the AAR’s Manual of Standards & Recommended Practices (MSRP), Section F – Sensors / S-920, specifically to Appendix A: Wheelset Data Glossary, Axle Bar Code, Element C307 — Axle AAR Condition Code. The circular introduces a new code—Condition Code 4—to improve visibility in the Component Registry for downsized or converted axles still classified as new, and notes that the Component Registry user community will be notified when the modification goes live through an upcoming Railinc release notification.
Date: 01-28-2026
Effective Date: 01-28-2026
C-14728
Subject: Implementation Circular: Revisions to MSRP F, Sensors, S-6102, Wayside Passing Data Format | Acoustic Bearing Detector (ABD) Readings
Summary: The Equipment Health Monitoring Committee (EHMC) is issuing this circular to advise the industry of modifications to the subject section of AAR’s Manual of Standards & Recommended Practices (MSRP), Section F – Sensors. These modifications add industry-approved elements and supplemental information related to acoustic bearing detector (ABD) data transmitted to Railinc for the creation of Equipment Health Management System (EHMS) alerts.
Date: 01-28-2026
Effective Date: 01-28-2026
C-14729
Subject: Implementation of Revisions to AAR Intermodal Interchange Rules, Appendix F, Standardize the Why Made Descriptions
Summary: This circular letter notifies the industry of revisions to AAR Intermodal Interchange Rules, Appendix F, to standardize the Why Made Descriptions. It references a previous circular letter issued to solicit comments, states no comments were received, and announces that the revised rules are now implemented and effective immediately.
Date: 01-28-2026
Effective Date: 01-28-2026
C-14730
Subject: Implementation of Revisions to MSRP Section G, WHEELS AND AXLES, M-101 Axles, Carbon Steel, Heat Treated, Class F Production, Straightening, and Chemical Composition
Summary: This circular letter notifies the industry of revisions to Section G, WHEELS AND AXLES, M-101 Axles, Carbon Steel, Heat Treated, including the discontinuation of Class F axle production after March 1, 2026, updates to axle straightening requirements, and chemical composition requirements. It references a previous solicitation for comments (Circular Letter C-14675) and announces that the revised standard M-101 is now implemented and effective immediately.
Date: 01-28-2026
Effective Date: 01-28-2026
C-14731
Subject: Implementation of Revisions to MSRP Section B, FREIGHT CAR DRAFT COMPONENTS, Specification M-118, re. archiving of M-118, creation of new standards S-123 and S-124, migration to MSRP S-III, COUPLER AND YOKE DETAILS, and new C-10A alternate pin end detail
Summary: This circular letter notifies the industry of the implementation of Section S-III, COUPLER AND YOKE DETAILS, Standards S-123 and S-124 which replace Specification M-118 from Section B, FREIGHT CAR DRAFT COMPONENTS. It details updates including revised drawings, clarified hardness testing requirements, and added new standards and pin end details, with changes made in response to comments received.
Date: 01-28-2026
Effective Date: 01-28-2026
Call for Comment
C-14719
Subject: DRAFT S-9166.V1.0 Consist Discovery Component Requirements, in support of AAR’s MSRP – Section K-II Locomotive Electronics and Train Consist System Architecture
Summary: The Railway Electronics Standards Committee (RESC) of the Association of American Railroads (AAR) is publishing DRAFT S-9166.V1.0 Consist Discovery Component Requirements for review and comment. This document specifies an industry standard for LCC Consist Discovery behavior, including the consumption and publication of Consist Discovery messages among locomotives on the consist.
Date: 01-06-2026
Comment Period: 30-day
C-14724
Subject: DRAFT S-9311.V1.0 LCC Consist Discovery ICD, in support of AAR’s MSRP – Section K-IV Office Architecture and Railroad Electronics Messaging
Summary: The Railway Electronics Standards Committee (RESC) of the Association of American Railroads (AAR) is publishing DRAFT S-9311.V1.0 LCC Consist Discovery ICD for review and comment. This document describes an industry standard for LCC Consist Discovery ICD message structure and provides a 30-day comment period starting from the posted date.
Date: 01-14-2026
Comment Period: 30-day
CPC-1439
Subject: Solicitation of Comments on Proposed Revisions to MSRP Section C Part III, M-1002, Specifications for Tank Cars, Appendix B, 3.6-Demonstration Capability: C6r
Summary: The Tank Car Committee has accepted the proposed revisions to Appendix B, section 3.6.15, activity code C6r. This action will allow facilities to accomplish the C6r demonstrations by either displaying modifications on tank car service equipment or by removing and replacing the service equipment and demonstrating the administration process of the modification.
Date: 01-16-2026
Comment Period: 30 Days
Notice of Circulars
C-14722
Subject: SAVE THE DATE – 2026 North American Railcar Mechanical Operations (NARMO) Seminar
Summary: The Association of American Railroads announces the 39th North American Railcar Mechanical Operations (NARMO) Seminar to be held from August 31 to September 3, 2026, in Denver, CO. The seminar aims to educate car owners, shippers, car shop operators, and railroad mechanical personnel on mechanical inspections, AAR Interchange Rules, and key industry systems.
Date: 01-09-2026
Effective Date: 01-09-2026
C-14725
Subject: Spring 2026 AAR Technical Committee Meetings
Summary: AAR meetings planned for the first half of 2026 are listed with details including dates, locations, and contacts for various technical committees. Information for individual Technical Committee Meetings can be found online and will be updated as the meetings approach.
Date: 01-23-2026
Effective Date: 01-23-2026
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