Interpretation ID: aiam1352
Project Engineer
Blue Bird Body Company
P.O. Box 937
Fort Valley
GA 31030;
Dear Mr. Milby: This is in reply to your November 8, 1973, request for a interpretation of the warning signal requirements of Standard No. 121, *Air brake systems*.; S5.1.5 of that standard states: >>>A signal, other than a pressure gauge, that gives a continuou warning to a person in the normal driving position when the ignition is in the 'on' or 'run' position and the air pressure in the service reservoir system is below 60 psi. The signal shall be either visible within the driver's forward field of view, or both audible and visible.<<<; A warning that 'the air pressure in the service reservoir system i below 60 psi' is intended to mean that a warning device's sensor could be located in the system you described in your letter between the source of air pressure and the check valve(s) required by S5.2.1.5. As you pointed out, this location would sense pressure below 60 psi anywhere from the compressor through the entire service reservoir system. A single warning installed before the check valves in a split service brake system would fulfill the requirements of S5.1.5 as long as it is positioned to sense pressure below 60 psi in any part of the split service reservoir system.; Your interpretation of the signal requirements is correct. The signa must be both audible and visible, or it must be visible within the driver's forward field of view. A simple audible signal is insufficient, as is a simple visible signal which is not within the driver's forward field of view.; Yours truly, Richard B. Dyson, Assistant Chief Counsel