Interpretation ID: aiam5019
Inc. 6131 Brookhill Drive Houston
Texas 77087-1131;
Dear Mr. Sonzala: Thank you for your letter regarding Federal Moto Vehicle Safety Standard No. 121, Air Brake Systems. Your company is a manufacturer of air brake systems and is apparently having difficulty selling your product to vehicle manufacturers because of a compliance issue related to Standard No. 121. I am pleased to provide you the following information. By way of background information, the National Highway Traffic Safety Administration (NHTSA) issues Federal motor vehicle safety standards under the National Traffic and Motor Vehicle Safety Act (Safety Act). The agency does not provide approvals of motor vehicles or motor vehicle equipment. Instead, the Safety Act requires manufacturers to certify that their vehicles or equipment comply with applicable safety standards. Standard No. 121 specifies braking requirements for vehicles equipped with air brake systems. The purpose of the standard is to ensure safe braking performance under normal and emergency conditions. The standard applies only to motor vehicles and not to motor vehicle equipment. Therefore, vehicle manufacturers are responsible for ensuring compliance with the standard, and not brake equipment manufacturers such as ITI. The dispute between ITI and the vehicle manufacturers (you use the term 'original equipment manufacturers') relates to the standard's parking brake requirements. The specific requirement at issue, set forth at S5.6 of Standard No. 121, requires a vehicle's parking brake to meet certain grade holding requirements (or other equivalent requirements) with 'any single leakage-type failure' of certain parts, including service brake chamber diaphragms. The purpose of this requirement is to ensure that a driver can safely park his or her vehicle in the event of a leakage-type failure in the service brake system. Leakage-type failures include such things as ruptured or severed brake hoses and torn diaphragms. Since these types of failures are relatively common in air brake systems, NHTSA believes that it is important that drivers be able to safely secure heavy trucks and other vehicles with such failures, until the vehicles can be repaired. For the purpose of determining whether a vehicle can meet Standard No. 121's grade holding requirements with one particular leakage-type failure, a failed diaphragm, IT would like the standard to be interpreted to cover only a very limited and specific type of failure, i.e., a hole 1/8 inch in size located in a particular place. Your letter states that the vehicle manufacturers generally have a broader view of what constitutes a failed diaphragm, i.e., they believe that failures include holes larger than 1/8 inch. You argue that Standard No. 121 is ambiguous in this area and requests NHTSA to issue an interpretation supporting your position. After reviewing this matter, we can state that the vehicle manufacturers are correct in their understanding that a failed diaphragm is not limited to a diaphragm wit a 1/8 inch hole. Therefore, if a vehicle cannot pass Standard No. 121's grade holding test with a larger hole in a failed diaphragm, the vehicle manufacturer cannot certify that the vehicle complies with the standard. Further, we disagree with ITI's contention that Standard No. 121 is ambiguous as to what constitutes a failed diaphragm. As indicated above, Standard No. 121 specifies that the grade holding requirements must be met with any single leakage-type failure of certain parts, including a failed diaghragm. The usage of the term 'any,' when used in connection with a set of items, is specifically designed at 49 CFR 571.4 as meaning the totality of that set of items, any one of which may be selected by the Administration for testing. Thus, a vehicle must meet the grade holding requirements regardless of the extent of the failure selected by NHTSA for testing. We note that leakage-type failures of many types and sizes can occur in vehicle brake systems. NHTSA intentionally did not limit the size or location of such failures in developing this requirement to ensure that a vehicle has adequate grade holding performance regardless of the specific nature of such a failure. You also asked whether other broken components, such as heavy parking springs, brake shoes, linings, and drums should be part of Standard No. 121's test requirements, since diaphragms are tested when torn. Although NHTSA's brake standards do not have any express test requirements for broken parking springs, brake shoes, linings or drums, those standards include a number of requirements to ensure adequate braking performance in the event of various failure in a vehicle's brake system. We hope that this information is helpful. Sincerely, Paul Jackson Rice Chief Counsel Enclosure;