Interpretation ID: aiam3977
Executive Vice President
X-Ten Corporation
855 Sansome Street
San Franciso(sic)
California 94111;
Dear Mr. James: this responds to your letter to Mr. Kratzke of my staff, asking for a interpretation of the requirements of Standard No. 121, *Air Brake Systems* (49 CFR S571.121). Specifically, you asked if the timing requirements of S5.3.3 and S5.3.4 must be satisfied by trailers which are 'heavy hauler trailers' within the meaning of S4. As Mr. Kratzke told you in a telephone conversation, heavy hauler trailers are exempted from all the requirements of S5.3, including the timing requirements.; You stated that your company is manufacturing extendable containe chassis trailers. The brake lines in those vehicles are designed to extend with the vehicle frame. S4 of Standard No. 121 defines, in part, a heavy hauler trailer as a trailer whose 'brake lines are designed to adapt to separation or extension of the vehicle frame...' Thus, your trailer would be considered a heavy hauler trailer for the purpose of Standard No. 121.; Section S5.3 sets forth road test requirements, compliance with whic must be certified for all trucks, buses and trailers. Generally, all trailers are required to be certified as complying with the timing requirements of S5.3.3 and S5.3.4. This general rule is limited by the last sentence of the S5.3, which specifies, 'However, *a heavy hauler trailer* and the truck and trailer portions of an auto transporter *need not meet the requirements of S5.3*' [Emphasis added] Thus, heavy hauler trailers are expressly exempted from all the requirements of S5.3, including the timing requirements.; If you have any further questions, please let me know. Sincerely, Jeffrey R. Miller, Chief Counsel