Interpretation ID: nht80-3.3

DATE: 06/11/80

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Flyer Industries Limited

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your April 7, 1980, letter asking whether you would be exercising due care if you alter the test procedures in Standard No. 121, Air Brake Systems. You propose to change the brake linings that are currently used on some of your vehicles. You would prefer to conduct decelerometer and stopping distance tests to assure compliance of your vehicles and dispense with the dynamometer test requirements.

The test requirements of Standard No. 121 are a means of establishing that you are in compliance with the performance requirements of the standard. However, like all of the agency's safety standards, it is not legally required that a manufacturer conduct the tests as they are stated in the standard if the manufacturer has an alternate procedure such as computer simulation, mathematical calculation, etc. which it is confident can equally prove the compliance of its vehicles. It is up to the manufacturer to establish in its own mind that any alternate procedure is an exercise of due care adequate to assure it would conform to the standard if the actual tests were conducted.

With respect to the particular test that you propose to conduct, the agency notes that the stopping distance and decelerometer tests are used to test for several aspects of brake performance that are regulated by the standard. The dynamometer tests are used to establish the fade resistance and recovery performance of the brake linings. The agency does not believe that stopping distance tests alone can measure, in particular, the fade resistance of the brake linings. Accordingly, we do not believe that you could certify your vehicle in compliance without some tests or analysis for fade resistance. This does not mean that you must conduct the dynamometer test, however, if you have another technique which you believe adequately measures the fade resistance of the linings.

SINCERELY,

FLYER INDUSTRIES LIMITED

April 7, 1980

The Office of Chief Council National Highway Traffic Safety Administration

Dear Sirs:

We presently manufacture a transit coach certified for FMVSS 121 at a providing ground. Due to customer request, a brake lining deviation from the certified ABB80 to Carlisle B33 is required. Local dynamometer testing is extremely difficult.

Our proposal is to conduct deoelerometer and stopping distance tests to compare lining performance. Full service tests at both loads and on both surface co-efficients would be done, as these were most marginal during the proving ground test. (See charted results.) It is not planned to outfit the new linings with themocouples. If performances are as good or better than for the linings that were certified, we would take this as sufficient evidence of compliance.

Please advise if such testing, fully documented, would be considered due care. Prompt reply to enable test scheduling, will be greatly appreciated.

Todd Smith

CC: B. MOSS

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