Interpretation ID: nht76-5.77

DATE: December 9, 1976

FROM: Frank A. Berndt -- Acting Chief Counsel, U.S. Department of Transportation, NHTSA

TO: Leon W. Steenbock -- Engineering, FWD Corporation

TITLE: None

ATTACHMT: Attached to letter dated 5-6-93 from John Womack to Bob Brinton (A41; Std. 121); Also attached to letter dated 3-16-93 from Bob Brinton to NHTSA (OCC 8436)

TEXT: This responds to FWD Corporation's October 15, 1976, request to know whether a truck that complies with the requirements of Standard No. 121, AIR BRAKE SYSTEMS, would continue to comply after the addition or another parking brake system (hand-operated mechanical, operating on the driveline) or another service brake control (piped to either or both sides of a split system).

Standard No. 121's requirements for braking systems does not preclude the addition of an additional braking system. The agency would not consider the requirements of S5.6.4 to prohibit an additional parking brake control.

Standard No. 121 does not prohibit installation of more than one service brake control. The installation of a hand-operated control lever that your letter appears to describe would not of itself violate the standard's requirements. If the hand control were piped into both systems, however, a failure introduced into the control would probably result in violation of S5.7.1, which requires certain secondary braking performance following a single failure introduced into the service brake system.