Interpretation ID: aiam1594
Sales Engineer
Highway Products
B.F. Goodrich Aerospace and Defense Products
P.O. Box 340
Troy
OH 45373;
Dear Mr. Burt: This responds to your June 4 and June 20, 1974, letters asking if parking brake system which locks mechanically after the brake is applied by any emergency air supply acting through the service air brake chamber would comply with Standard No. 121, *Air brake systems*. The parking brake provisions require in part:; >>>S5.6.3 *Application and holding*. The parking brake shall be applie by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system. Once applied, the parking brakes shall be held in the applied position solely by mechanical means.<<<; The arrangement described would not meet this requirement because th energy source to apply the brakes (the emergency air supply) would be affected by loss of air pressure in the service brake system. For example, any failure in the service brake piston diaphragm would cause a loss of air pressure that would in turn 'affect' the energy source that applies the parking brakes. The brake chamber housing assembly is an element which is not considered to be part of the service brake system for this requirement.; I would like to point out that the provisions of Standard No. 121 d not apply to trailers manufactured before January 1, 1975.; Yours truly, Richard B. Dyson, Acting Chief Counsel