Interpretation ID: nht78-2.50

DATE: 01/20/78

FROM: AUTHOR UNAVAILABLE; F. Berndt for J. J. Levin, Jr.; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Bendix Corporation's November 9, 1977, request for 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 address 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 that "[the] 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.