Federal Motor Vehicle Safety Standards; Air Brake Systems

In a May 3, 1989 final rule, NHTSA changed the brake applications and release timing requirements of the Federal motor vehicle safety standard on air brake systems. The changes to these requirements resulted in the addition of a new schematic diagram of a trailer test rig, labeled as Figure 1, to the standard. A pre-existing trailer test rig schematic was re-labeled as Figure 1(a) and retained for use until the new brake application and release timing requirements and the new figure became effective May 3, 1991. We are now deleting the obsolete Figure (1)(a). A provision describing the pressure characteristics of the trailer test rig depicted in Figure 1(a) is also being deleted. We are also taking this opportunity to correct various minor errors and omissions in the standard.