Interpretation ID: aiam2731
Group Director of Engineering
The Bendix Corporation
901 Cleveland Street
Elyria
OH 44035;
Dear Mr. Hildebrandt: This responds to Bendix Corporation's November 9, 1977, request fo confirmation that S5.6.4 of Standard No. 121, *Air Brake Systems*, does not prohibit the use of a two-valve sequential means to release the parking brakes on a towed vehicle.; I have enclosed for your information two interpretations that addres this question, stating that a two- valve sequential release is permissible under S5.6.4. I have also enclosed a copy of an outstanding rulemaking proposal that would standardize the parking brake control as specified in the Society of Automotive Engineers Recommended Practice J680b. I am unable to advise you whether the National Highway Traffic Safety Administration intends to make final this proposal.; I would also like to remind you of the requirement in S5.6.4 tha '[t]he control shall be identified in a manner that specifies the method of control operation.' So long as different control arrangements are used, it is critical that the means of operation be clearly marked.; Joseph J. Levin, Jr.