Interpretation ID: aiam3075
Director of Engineering
The Berg Manufacturing Company
P.O. Box 368
Iola
KS 66749;
Dear Mr. Crail: This responds to your June 28, 1979, letter asking several question about the compliance of your trailers with Standard No. 121, *Air Brake Systems*.; You first ask whether section S5.6.3 allows the use of service air t apply the parking brakes as long as a source of energy to apply the parking brakes is available at all times and is unaffected by any single failure in the service brake system. The answer to this question is yes. On August 9, 1979, the agency published in the Federal Register a notice amending section S5.6.3 of the standard to permit the type of parking brake system that you outlined in your letter.; In your second question, you ask whether your braking system complie with section S5.2.1.1. That section requires that a reservoir be provided that is capable of releasing the vehicle's parking brakes and that is unaffected by the loss of pressure in the service brake system. Your trailer has a tank and valve for each axle. You state that in the event of a service system failure including a failure of one of the tanks, that a reservoir is available such that when the supply line is pressurized to 55 psi, the vehicle's parking brakes will release. Assuming that your system operates as you have detailed in your letter, the agency concludes that it complies with S5.2.1.1 of the standard.; Sincerely, Frank Berndt, Chief Counsel