Interpretation ID: aiam1700
Hadco Engineering
2000 Camfield Avenue
Los Angeles
CA 90040;
Dear Mr. Miller: This responds to your November 13, 1974, question whether a combinatio vehicle which consists of an air- braked truck tractor and an electrically-braked trailer would be subject to the requirements of Standard No. 121, *Air brake systems*, effective January 1, 1975, for trailers and March 1, 1975, for trucks and buses. The electric brakes on the trailer would be actuated by a Warner Electric brake controller that is designed to be mounted in the truck's air control line to respond to air brake signals generated by the truck's service brake control.; Standard No. 121 applies to trucks, buses, and trailers equipped wit air brake systems. Therefore, the trailer which is electrically-braked is not required to comply with the standard.; It appears from the Warner literature that you enclosed that the truc tractor would be equipped with air brakes and would therefore have to comply with the standard. I would like to point out that air-braked truck tractors manufactured after March 1, 1975, must be certified to comply with the requirements of the air brake standard. If a person modifies the air brake lines on such a truck tractor before the first retail purchase by the addition of the Warner controller, that person must certify that the truck still meets the standard as modified.; Yours truly, Richard B. Dyson, Acting Chief Counsel