North Carolina CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

What happens if a major leak lets all the air out of the brake system?

Accepted Answer

The springs apply the brakes — Because the springs are normally held off by air pressure, losing all of the system's air lets them snap on and brake the vehicle.

Answer

The service brakes lock only the front wheels

Answer

Nothing happens until you press the pedal

Answer

The compressor keeps the vehicle stopped on its own

Question 2

When the low-air warning first lights up while driving, what should you do?

Accepted Answer

Come to a controlled, safe stop immediately, before you lose the ability to brake — Don't wait for the spring brakes to grab on their own; stop safely as soon as the warning appears, while braking is still under your control.

Answer

Keep going and pump the pedal to rebuild pressure

Answer

Wait for the spring brakes to stop the vehicle automatically

Answer

Release the parking brake control to add air

Question 3

While you drive, what holds the powerful spring brakes in the released position?

Accepted Answer

Air pressure in the system — Air pressure compresses and holds back the springs while driving; if that air escapes, the springs apply the brakes.

Answer

A mechanical latch on the slack adjuster

Answer

The alcohol evaporator

Answer

The stop light switch

Question 4

On a tractor or straight truck, the spring brakes come fully on when air pressure falls into roughly what range?

Accepted Answer

20 to 45 psi — As pressure bleeds down to about 20 to 45 psi (often 20 to 30), the springs fully apply, so you should stop while you still have air to control the brakes.

Answer

50 to 75 psi

Answer

85 to 100 psi

Answer

120 to 140 psi

Question 5

A visible low-air-pressure warning must come on before tank pressure drops below what level?

Accepted Answer

Below 60 psi — Air-brake vehicles must have a warning you can see that activates before pressure falls under 60 psi (or half the cut-out pressure on some older trucks).

Answer

Below 100 psi

Answer

Below 85 psi

Answer

Below 45 psi

Question 6

Where is the yellow ABS malfunction lamp located on a trailer?

Accepted Answer

On the left side, at a front or rear corner — A trailer's yellow ABS malfunction lamp is mounted on its left side, at either the front or the rear corner.

Answer

On the rear bumper, centered

Answer

Inside the tractor cab

Answer

On the right-side landing gear

Question 7

What causes brakes to fade?

Accepted Answer

Excessive heat from overusing the service brakes instead of engine braking — Riding the service brakes builds heat that changes the lining and expands the drums, weakening braking; using engine braking on grades helps prevent fade.

Answer

Draining the air tanks too often

Answer

Filling the alcohol evaporator in warm weather

Answer

Setting the parking brake while moving

Question 8

What is the purpose of a modulating control valve?

Accepted Answer

To let the driver apply the spring brakes gradually if the service brakes fail — The spring-loaded modulating handle lets you apply the spring brakes gradually, giving you controlled braking if the service brakes quit.

Answer

To drain the tanks gradually overnight

Answer

To limit front-brake pressure on ice

Answer

To recharge the trailer air tanks

Question 9

What is a 'wig wag' device?

Accepted Answer

A mechanical arm that drops into the driver's view when pressure falls below about 60 psi — The wig wag is one form of low-air warning; its arm swings down into the driver's view when system pressure drops under roughly 60 psi.

Answer

A valve that limits air to the front brakes on ice

Answer

A second gauge that shows trailer tank pressure

Answer

A lever used to apply the spring brakes gradually

Question 10

Some buses have a separate air tank tied to a dual parking control valve. What is it for?

Accepted Answer

To let the spring brakes off so a stalled bus can be repositioned in an emergency — Pushing the control sends air from that reserve tank to release the spring brakes so the vehicle can be moved in an emergency, but there is only enough for a few uses.

Answer

To supply extra pressure to the front brakes

Answer

To power the ABS computer if the main system fails

Answer

To keep the alcohol evaporator filled

Question 11

Why is repeatedly pumping (fanning) the brake pedal when it isn't needed a bad habit in an air-brake vehicle?

Accepted Answer

It can release air faster than the compressor can replace it, dropping pressure too low — Each release lets some air out of the system; needless pumping can drain the tanks faster than the compressor rebuilds them, and if pressure falls too far the brakes stop working.

Answer

It overheats the alcohol evaporator

Answer

It forces the governor into an early cut-out

Answer

It permanently locks the spring brakes

Handling Emergencies

Study questions with answers

1. What happens if a major leak lets all the air out of the brake system?

2. When the low-air warning first lights up while driving, what should you do?

3. While you drive, what holds the powerful spring brakes in the released position?

4. On a tractor or straight truck, the spring brakes come fully on when air pressure falls into roughly what range?

5. A visible low-air-pressure warning must come on before tank pressure drops below what level?

6. Where is the yellow ABS malfunction lamp located on a trailer?

7. What causes brakes to fade?

8. What is the purpose of a modulating control valve?

9. What is a 'wig wag' device?

10. Some buses have a separate air tank tied to a dual parking control valve. What is it for?

11. Why is repeatedly pumping (fanning) the brake pedal when it isn't needed a bad habit in an air-brake vehicle?

More CDL — Air Brakes topics

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