Interpretation ID: aiam1507
Chief Product Engineer
Certain-Teed Products Corporation
P.O. Box 366
Lawrence
KS 66044;
Dear Mr. Sibley: This responds to your April 5, 1974, question whether S5.6.1 or S5.6. of Standard No. 121, *Air brake systems*, requires parking brakes on all axles other than front steerable axles.; S5.6.1 requires 'parking brakes on an axle other than a steerable fron axle' to have certain static retardation force values. 'An axle' refers to any axle other than steerable front axles and therefore S5.6.1 requires parking brakes on all axles other than steerable front axles. A tandem axle consists of two separate axles for purposes of this requirement.; S5.6.2 has no specific axle-by-axle requirements. Its performanc standard may be met by any means which hold the vehicle stationary and conform to S5.6.3 and S5.6.4. It should be emphasized that this requirement cannot be met simply by equipping the vehicle with parking brakes which hold to the limit of tractive ability but permit vehicle movement.; Yours truly, Richard B. Dyson, Assistant Chief Counsel