People seeking commercial driver's licenses are required to obtain endorsements specific to the types of vehicle they plan to operate. Since many commercial vehicles, such as large trucks, utilize air-braking systems, potential drivers of these rigs must demonstrate their proficiency with air brakes by obtaining endorsements.
Potential drivers must have a keen understanding of the entire air-braking system as well as the location of air storage tanks, which must be drained daily. Familiarity with gauges and their use in identifying system leaks or defects is required.
Individuals must be proficient in performing walk-around inspections, which involve examination of air-compressor drive belts, slack adjusters and each brake's drum or disc linings. To perform daily inspections, aspiring drivers must know how to test a vehicle's low-pressure warning system.
According to the U.S. Department of Transportation, drivers are awarded their commercial driver's licenses and accompanying endorsements only after passing a written general knowledge test as well as a skills test. If a driver fails the testing procedures for an air-brake endorsement or takes the skills test with a vehicle that does not utilize air brakes, the individual is issued a license with an air-brake restriction.
