Interpretation ID: aiam2080
Counsel
Kelsey-Hayes Company
Romulus
MI 48174;
Dear Mr. McCuen: This responds to Kelsey-Hayes Company's July 28, 1975, question askin whether the requirements of S5.1.6 of Standard No. 121, *Air Brake Systems*, that specify a warning signal 'in the event of a total electrical failure of the antilock system' would permit installation on a vehicle of an antilock-equipped axle that has no capability signal electrical failure of its antilock system. You state that the vehicle would be equipped with antilock systems on other axles that would provide a warning signal in the event of their electrical failure.; The answer to your question is yes. As you noted in your letter, th National Highway Traffic Safety Administration has interpreted the specifications of S5.1.6 to require a signal only in cases where electrical failure within the antilock electrical system circuity causes loss of antilock control of every wheel on the vehicle. In the design you describe, the signal which activates upon loss of antilock control at one or more wheels on the vehicle would fulfill this requirement, because it would always activate by the time antilock control had been lost at every wheel on the vehicle. Under our interpretation of S5.1.6, a failure of antilock only on the axle described by you would not constitute 'loss of antilock control of every wheel on the vehicle' and would not be required to be signaled.; Sincerely, Frank A. Berndt, Acting Chief Counsel