Air Brake Test Legal Requirements & Compliance 2

Question 1

Under FMCSA regulations, what is the minimum brake lining/pad thickness before a vehicle must be placed out of service?

Accepted Answer

Linings must be replaced before metal-to-metal contact; specific minimums vary by axle position per 49 CFR 393

Answer

1/8 inch for all axle positions

Answer

1/4 inch for all positions

Answer

Lining thickness is not regulated federally

Question 2

What does 49 CFR Part 393 regulate with respect to air brakes?

Accepted Answer

The parts and accessories required on commercial motor vehicles, including specific air brake system standards

Answer

Only the CDL testing requirements for drivers

Answer

Emissions standards for air compressors

Answer

Roadside inspection procedures for enforcement officers only

Question 3

Which agency is primarily responsible for enforcing air brake safety regulations on commercial vehicles in the United States?

Accepted Answer

Federal Motor Carrier Safety Administration (FMCSA)

Answer

National Transportation Safety Board (NTSB)

Answer

Department of Transportation Office of Inspector General

Answer

Environmental Protection Agency (EPA)

Question 4

What is the air brake endorsement requirement for CDL holders who drive vehicles with air brakes?

Accepted Answer

Drivers must not have an air brake restriction (L restriction) on their CDL, obtained by passing the air brake knowledge and skills tests

Answer

Drivers need a separate Air Brake Endorsement added to their CDL

Answer

Only Class A CDL holders need air brake authorization

Answer

No specific authorization is needed beyond the base CDL

Question 5

Under the Federal Motor Carrier Safety Regulations, how often must air tanks be drained?

Accepted Answer

At least once a day, or more frequently as needed based on conditions

Answer

Once per week during pre-trip inspection

Answer

Only when the air dryer is serviced

Answer

Every 10,000 miles as part of scheduled maintenance

Question 6

What is the 'out-of-service' (OOS) criterion for air brake system leak rates during a roadside inspection?

Accepted Answer

Pressure loss exceeding 3 psi per minute for single vehicles or 4 psi per minute for combination vehicles at a single service brake application

Answer

Any detectable air leak at any fitting

Answer

A pressure drop of more than 10 psi in 5 minutes with brakes released

Answer

Only leaks visible as air bubbles in soapy water trigger OOS