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-14632
Subject: Implementation of Revisions to MSRP Section C-I, CAR CONSTRUCTION FUNDAMENTALS AND DETAILS, Standard S-234, and Section C-II M-1001 DESIGN, FABRICATION, AND CONSTRUCTION OF FREIGHT CARS, regarding jacking and lifting requirements
Summary: This circular notifies the industry of revisions to MSRP Section C-I, CAR CONSTRUCTION FUNDAMENTALS AND DETAILS, Standard S-234 Jacking and Lifting of Freight Cars, and Section C-II M-1001 DESIGN, FABRICATION, AND CONSTRUCTION OF FREIGHT CARS, regarding jacking and lifting requirements. The revisions improve the description of jacking and lifting requirements to address issues encountered during handling of recently built cars and include updated guidance and requirements for jacking clearances, electronic jack gage availability, lifting hook updates, and truck removal requirements.
Date: 11-03-2025
Effective Date: 11-03-2025
C-14668
Subject: IMPLEMENTED, AAR Manual of Standards and Recommended Practices (MSRP) Section K-I Railway Electronics System Architecture and Concept of Operations, Standard S-9051 ITC OPA Requirements External Content V0.0
Summary: External Content V0.0 to ITC Onboard PTC Application (OPA) Requirements, S-9051, specifies the OPA requirements for interoperable PTC for the initial version of OPA software that supports Positive Train Control Office – Locomotive Segment – Interface Control Document (ICD), S-9361.V3.1, which specifies Interface Version 4 (IV4). The update frequency of the AAR document and the content of this External Content are not the same, therefore the information in the external content is stored separately from the document. Nevertheless, this information shall be considered part of Standard S-9051.
Date: 11-03-2025
Effective Date: 11-03-2025
C-14669
Subject: Implementation of Revisions to MSRP Section C-I, CAR CONSTRUCTION FUNDAMENTALS AND DETAILS, Standard S-2044, Safety Appliance Requirements for Freight Cars, Editorial Updates to Appendices F1 and F2
Summary: This circular letter notifies the industry of revisions to MSRP Section C-I, CAR CONSTRUCTION FUNDAMENTALS AND DETAILS, Standard S-2044, Safety Appliance Requirements for Freight Cars. The drawings in Appendix F1 and Appendix F2 were reformatted to better illustrate how to measure clearance for the highest handhold at the BL corner and at the AR corner.
Date: 11-03-2025
Effective Date: 11-03-2025
C-14687
Subject: Implementation Circular: Additions to MSRP F, Sensors, S-6101A –Detector Validation Table
Summary: This implementation circular is being released to the industry for revisions to the AAR’s Manual of Standards & Recommended Practices (MSRP) Section F – Sensors / S-6101A: Detector Validation Table / Acoustic Bearing Detectors. AAR’s Equipment Health Monitoring Committee (EHMC) voted to progress the standard to implementation following the action of the Wheels, Axles, Bearings & Lubrication Committee (WABL). The implemented standard is attached as reference.
Date: 11-17-2025
Effective Date: 11-17-2025
C-14689
Subject: Implementation of Revisions to MSRP Section S-III, COUPLER AND YOKE DETAILS, Standards S-108, S-155, and S-165, regarding MSRP references and coupler butt dimensions and tolerances for E68DE, SBE68DE, and SE68DE couplers
Summary: This circular letter notifies the industry of the implementation of revisions to Section S-III Standards S-108, S-155, and S-165 concerning coupler and yoke details. The changes include improved image quality, added butt dimensions, added references to other standards, and notes on dimension tolerances.
Date: 11-24-2025
Effective Date: 11-24-2025
C-14690
Subject: Implementation of a New Figure for Shipping Glass Panel Products on Center A-Frame Flatcars – Section 5 of the AAR Open Top Loading Rules Manual (OTLR)
Summary: The AAR’s Open Top Loading Rules Committee (OTLRC) has approved the addition of Figure 130 to Section 5 of the OTLR manual, which details the packaging and securing of glass panel products on center A-frame flatcars. This new figure includes specifications for packaging, securement straps, package bands, and cables, and the implementation is effective immediately with instructions for interim use of the circular attachment.
Date: 11-24-2025
Effective Date: 11-24-2025
CPC-1434
Subject: Implementation of Revisions to MSRP Section C Part III, M-1002, Specifications for Tank Cars, Proposed Appendix A
Summary: Comments received from CPC-1430 have been addressed. This is the final action on revisions affecting Appendix A, Tank Car Valves and Fittings, of M-1002, Specifications for Tank Cars. The Tank Car Committee authorized the replacement of table A.2 in Appendix A with D.6 from Appendix D- (AAR component tracking effective dates) in the MSRP-CIII, Specifications of Tank Cars (M-1002). This table now includes serial numbers marked at the time of initial manufacturing or assembling and AAR component tracking effective dates.
Date: 11-07-2025
Effective Date: 11-07-2025
Call for Comment
C-14674
Subject: Solicitation of Comments: Revisions to MSRP F, Sensors, S-6102, Wayside Passing Data Format | Hot Bearing Detector (HBD) Readings
Summary: The Equipment Health Monitoring Committee (EHMC) is releasing this circular to solicit comments on the proposed addition to the subject section within AAR’s Manual of Standards & Recommended Practices (MSRP), Section F – Sensors. The proposed additions to this standard are specific to Section 2.4.2 HBD Detector Readings – Extension of Readings, which will initially be listed as optional elements but may become mandatory in the future.
Date: 11-12-2025
Comment Period: 30 Days
C-14675
Subject: Solicitation of Comments for 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 solicits comments for proposed revisions to MSRP Section G, WHEELS AND AXLES, M-101 Axles, Carbon Steel, Heat Treated, to no longer permit the production of Class F axles after March 1, 2026, update of the axle straightening requirements, and update of the axle chemical composition requirements. The proposed revision to M-101 does not have costs associated with implementation.
Date: 11-12-2025
Comment Period: 30 Days
C-14676
Subject: Solicitation of Comments for Revisions to MSRP Section G, WHEELS AND AXLES, M-107/M-208, S-670, S-671, S-672, S-673, AAR-2A Flange Thickness, Height, and Throat Radii Gauges, Corrosion Resistant Coatings, Records, and Ultrasonic Testing Rejection
Summary: This circular letter solicits comments for proposed revisions to MSRP Section G, WHEELS AND AXLES, M-107/M-208, and the creation of new standards S-670, S-671, S-672, and S-673. The revisions include updates to flange thickness, height, and throat radii gauges, corrosion resistant coatings, record retention requirements, ultrasonic testing rejection analysis, and facility audit requirements.
Date: 11-12-2025
Comment Period: 30 Days
C-14678
Subject: DRAFT S-9501.V5.0 Positive Train Control Data Model Definition, in support of AAR’s MSRP – Section K-VI Railway Data Management and Communications
Summary: The Positive Train Control Interoperability Committee (PTCIC) of the Association of American Railroads (AAR) is publishing DRAFT S-9501.V5.0 Positive Train Control Data Model Definition for review and comment. The purpose of the PTC Data Model format is to establish a common data format between the various railroad databases to facilitate the conversion of track data for use by positive train control applications.
Date: 11-12-2025
Comment Period: 10-day
C-14679
Subject: Solicitation of Comments, Revisions to Office Manual Rule 112 & CRB Procedures Manual, CBA Authorization for Exceptions Related to Aggregate Tax Billing
Summary: The circular discusses proposed modifications to Office Manual Rule 112 and the CRB Procedures Manual to address billing exceptions related to aggregate tax submissions. It includes details on current and proposed rules for tax billing and invoice summary billing, as well as mandatory use of the CRB Electronic Exceptions System for submitting billing exceptions.
Date: 11-12-2025
Comment Period: 30 Days
C-14688
Subject: Solicitation for Comments – Revision to MSRP Section N, Standard S-810, Field Impact and Over-the-Road Tests of Multi-Level Tie-Down Equipment and Methods
Summary: The Specially Equipped Freight Car Committee has proposed a revision to Standard S-810, Section 4.2 that will require an official AAR observer to witness and document results. The proposed revision includes criteria for acceptance or rejection of tie-down devices or methods and solicits comments from interested parties within 30 days of issuance.
Date: 11-20-2025
Comment Period: 30 Days
C-14694
Subject: Solicitation of Comments for Revisions to MSRP Section C CAR CONSTRUCTION FUNDAMENTALS AND DETAILS, new Specification M-803 Manufacturer of Major Subassemblies, Facility Approval, to replace requirements in Standard S-2034 Car Builder Certification
Summary: This circular letter solicits comments for MSRP Section C CAR CONSTRUCTION FUNDAMENTALS AND DETAILS, proposed Specification M-803 Manufacturer of Major Subassemblies, Facility Approval. The new M-803 specification sets forth requirements for manufacturers of freight car major subassemblies and would replace respective requirements in Standard S-2034 Car Builder Certification.
Date: 11-26-2025
Comment Period: 30 Days
Notice of Circulars
C-14670
Subject: Informational Circular, Revisions to Field Manual Rule 4.C, Painting of Air Brake Valves
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Brake Systems Committee, was reviewed and approved. The entire text of the revision is identified in the circular, stating that painting of air brake valves is not required, but if paint is applied, it must not obscure serial numbers and or built dates.
Date: 11-11-2025
Effective Date: 01-01-2026
C-14671
Subject: Informational Circular, Revisions to Field Manual Rule 16.E, Coupler Manufacturer Qualifier Chart
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Coupling System and Truck Castings Committee to revise Rule 16, was reviewed and approved. The entire text of the revision is identified, including the addition of new qualifiers to the Coupler Manufacturer Qualifier Chart.
Date: 11-11-2025
Effective Date: 01-01-2026
C-14672
Subject: Canceled
Summary: This circular letter informs all subscribers that the subject matter is canceled.
Date: 11-12-2025
Effective Date: 11-12-2025
C-14673
Subject: Canceled
Summary: This circular letter informs all subscribers that the subject matter is canceled.
Date: 11-12-2025
Effective Date: 11-12-2025
C-14677
Subject: Informational Circular, Revisions to Field Manual Rules 15, 16, 17 and 18, Couple Bodies
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Coupling System and Truck Castings Committee to revise Rules 15-18, was reviewed and approved. The document details the current and proposed revisions to Field Manual Rules 15.E.5, 16.E.4, 17.E.21, and 18.E.7 regarding the painting of coupler bodies and rotary system components.
Date: 11-12-2025
Effective Date: 01-01-2026
C-14680
Subject: Informational Circular, Revisions to Field Manual Rule 18, Coupler Bodies
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal to revise Rule 18 was reviewed and approved. The circular identifies the entire text of the revision and notes that these changes will be included in the January 1, 2026 release of the Field Manual.
Date: 11-14-2025
Effective Date: 01-01-2026
C-14681
Subject: Informational Circular, Revisions to Field Manual Rule 41.C.1, Figures 41.2 and 41.3
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal to add dimension to Field Manual Rule 41.C.1 Figures 41.2 and 41.3 was reviewed and approved. The circular includes the entire text of the revision and states that these changes will be included in the January 1, 2026 release of the Field Manual.
Date: 11-14-2025
Effective Date: 01-01-2026
C-14682
Subject: Informational Circular, Revisions to Field Manual Rule 41.C.1, High Flange Gaging
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal to add two new figures to Field Manual Rule 41 to define how to take a high flange reading was reviewed and approved. The circular provides the current and proposed figures and instructions on how to take high flange readings using various wheel gages.
Date: 11-14-2025
Effective Date: 01-01-2026
C-14683
Subject: Informational Circular, Revisions to Field Manual Rule 66, Reflectorization
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal to revise Field Manual Rule 66 to remove old dates and add clarification for reporting to Umler was reviewed and approved. The Reflectorization Date in Umler is intended to represent the last time a complete reflectorization event occurred, either initial application and complete renewal only.
Date: 11-14-2025
Effective Date: 11-14-2025
C-14685
Subject: Informational Circular, Revisions to Field Manual Rule 80, Markings
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Equipment Engineering Committee, was reviewed and approved. The circular details revisions to Field Manual Rule 80 regarding markings, including specifications for missing or illegible dates and reporting marks on cars.
Date: 11-14-2025
Effective Date: 01-01-2026
C-14691
Subject: Informational Circular, Revisions to Field Manual Rule 67, Job Code 4469
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, it was brought to the committee’s attention that revisions to Field Manual Rule 67 as identified in C-12734, had not been implemented as planned. Those revisions are identified in the circular and will be included in the January 1, 2026 release of the Field Manual.
Date: 11-25-2025
Effective Date: 11-25-2025
C-14692
Subject: Informational Circular, Revisions to Field and Office Manuals, Various Rules, Tank Cars
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Equipment Engineering Committee and the Tank Car Committee to revise various Field and Office Manual Rules was reviewed and approved. The entire text of the revision is identified in the circular, including changes to Field Manual Rules 1.3.h, 1.5.b(12), 72.E.8.b, 83.16 Car Part Codes, and Office Manual Rules 93.7, 107.F.1, 107.G Exhibit II, IV, and V.
Date: 11-25-2025
Effective Date: 01-01-2026
C-14693
Subject: Informational Circular, Revisions to Field Manual Rules 3 and 4, 4-Pressure Tests
Summary: At the October 2025 meeting of the Arbitration and Rules Committee, a proposal as advanced by the Brake Systems Committee to editorially revise Field Manual Rules 3 and 4, was reviewed and approved. The document details the current and proposed revisions to Field Manual Rules 3.B.4, 4.B.12-14, and 4.E.27-28 regarding 4-pressure tests and related procedures.
Date: 11-25-2025
Effective Date: 11-25-2025
CPC-1435
Subject: Cancellation of Midland Manufacturing Service Trial 429- Vacuum Relief Valve (A-210, A-211, A-212)
Summary: The vacuum relief in question did not complete service trial requirements. The Tank Car Committee voted to cancel service trial 429 at the October 2025 TCC Meeting. All units are to be removed in the next 3 years or by the next valve qualification date, whichever comes first.
Date: 11-07-2025
Effective Date: 11-07-2025
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