Interpretation ID: aiam1556
Group Director of Engineering
Heavy Vehicle Systems Group
The Bendix Corporation
901 Cleveland Street
Elyria
OH 44035;
Dear Mr. Hildebrandt: This responds to Bendix's June 10, 1974, request for interpretation o the Standard No. 121 requirement in S5.5.1 that 'on a vehicle equipped with an antilock system, electrical failure of any part of the antilock system shall not increase the actuation and release times of the service brakes.' You ask whether this language permits use of a separate device that senses electrical failure in the antilock system and automatically reduces pressure to the front brakes as a safety measure. The device would increase brake actuation and release time.; S5.5 is addressed to antilock systems and S5.5.1 mandates that antiloc systems be designed not to interfere with air brake performance if they fail electrically. S5.5.1 does not prohibit separate safety devices which are designed to operate in the event of antilock electrical failure to compensate for that failure. Therefore the Bendix automatic front axle limiting system, as we understand its operation, is not prohibited by S5.5.1 simply because it operates when it senses an antilock electrical failure.; Sincerely, Richard B. Dyson, Acting Chief Counsel