Iowa CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

In a truck with a dual air brake system, the low air light and buzzer come on. One gauge still reads 110 psi while the other is falling. What should you do?

Accepted Answer

Stop right away in a safe place, park, and get the air brakes fixed — The warning comes on before either system's pressure falls under 55 psi, and it means you should stop and park safely right away. With one system very low, either the front or the rear brakes are not working fully, so stops take longer. Get the air brake system repaired before going on.

Answer

Keep driving to your destination, since one system is still fully charged

Answer

Pump the brake pedal to shift air from the full system into the low one

Answer

Keep driving, but make your stops with the parking brake control only

Question 2

On Iowa's inspection test, you check the air lines between the power unit and an air-braked trailer. What does the manual say a low air condition can do to the trailer?

Accepted Answer

Set its spring brakes suddenly, which may cause a loss of control — Iowa's guide warns that losing air to the trailer can cost some or all of the towed unit's braking, and that low air makes the trailer's spring brakes come on abruptly, which may lead to a loss of control and a crash. That is why the air lines and connectors must be sound and free of leaks.

Answer

Release its brakes so it rolls freely behind the tractor

Answer

Turn off only its marker and brake lights

Answer

Raise its landing gear automatically

Question 3

What is the key difference between the controlled braking and stab braking methods for an emergency stop?

Accepted Answer

Controlled braking stays just short of locking the wheels; stab braking brakes fully and lets off whenever the wheels lock — Controlled braking means pressing as firmly as possible while stopping short of wheel lockup, with only tiny steering movements. Stab braking means braking all the way, letting off once the wheels lock, and braking fully again when they roll, which can take up to a second.

Answer

Controlled braking relies on the parking brake; stab braking relies on the foot brake

Answer

Controlled braking holds light, steady pressure; stab braking taps the pedal lightly and quickly

Answer

Controlled braking is meant for hydraulic brakes; stab braking is only for vehicles with ABS

Question 4

Braking hard on ice in a truck without ABS, you lock up the front steering wheels. What is the immediate result?

Accepted Answer

You can no longer steer the truck — Locked steering wheels take away your steering control, while lockup at the other wheels can bring on a skid, a jackknife, or a spin. ABS guards against this by sensing a wheel about to lock and easing brake pressure to a safe level.

Answer

The truck may jackknife, but steering stays normal

Answer

The spring brakes apply to free the wheels

Answer

The truck stops sooner because locked tires grip better

Question 5

While you're driving, a mechanical arm suddenly swings down into your view. What has happened?

Accepted Answer

The air pressure in the system has dropped below 55 psi — That arm is a wig wag, one type of low air pressure warning. It drops into view when system pressure falls under 55 psi. Treat it like the low air light and buzzer and bring the vehicle to a safe stop while you can still control the brakes.

Answer

The governor has cut out the compressor at about 125 psi

Answer

The ABS has sensed a wheel that is about to lock

Answer

The safety relief valve has opened at about 150 psi

Question 6

You use stab braking in an emergency and notice the rig is not straightening out between applications. What is the most likely mistake?

Accepted Answer

Reapplying the brakes before the wheels have started rolling again — In stab braking you apply the brakes fully, release them when the wheels lock, and apply them fully again once the wheels roll. It can take up to a second for locked wheels to start turning after you let off. If you brake again before they do, the vehicle won't straighten out.

Answer

Releasing the brakes as soon as the wheels lock

Answer

Applying the brakes all the way each time

Answer

Waiting up to a second for the wheels to begin turning

Question 7

A brake line on the primary side of your dual air brake system bursts, and that side loses its air. Why does the secondary side keep its pressure?

Accepted Answer

Each side has its own air tanks, hoses, and lines — A dual system is really two independent air brake systems worked through one set of brake controls, and each side keeps its own tanks, hoses, and lines. Losing one side does not empty the other, but either the front or rear brakes will then be short of full braking, so stopping takes longer. Pull over safely and get the system repaired.

Answer

The governor stops feeding the leaking side and sends all of its air to the other

Answer

The safety relief valve seals off the side that is leaking

Answer

The secondary side refills itself from the trailer's air tanks

Question 8

Glancing in your left mirror on the highway, you see a yellow lamp lit on the left side of your trailer. What is it most likely telling you?

Accepted Answer

The trailer's ABS may not be working at one or more wheels, though its regular brakes still work — Trailers carry their yellow ABS malfunction lamp on the left side, at the front or rear corner. If that lamp comes on while you're under way, ABS may have stopped working at one or more wheels. You still have regular brakes, so drive normally and get the system serviced soon.

Answer

The trailer's air tank is full of water and needs to be drained

Answer

The trailer's spring brakes are about to apply

Answer

The trailer's brake lights have burned out

Question 9

Your straight truck has ABS on all axles, but its yellow ABS lamp has stayed lit all day. A car stops suddenly ahead and you must brake hard. Which approach fits the manual?

Accepted Answer

Use controlled or stab braking, since the regular brakes still work but the wheels can now lock — A lamp that stays on means ABS may no longer be controlling one or more wheels. Your regular brakes still work, but you can't rely on ABS to prevent lockup, so the full-application exception for working ABS on all axles no longer applies. Use controlled or stab braking to keep the truck straight and steerable.

Answer

Stand on the pedal and hold it, since full application is allowed on a truck with ABS on all axles

Answer

Stop with the parking brake control alone, since the service brakes are tied to the failed ABS

Answer

Pump the pedal lightly until the lamp goes out, and only then brake hard

Question 10

You're using controlled braking in an emergency in a truck without ABS, and the wheels lock. What does the manual tell you to do?

Accepted Answer

Release the brakes, then put them back on as soon as you can — Controlled braking means braking as firmly as possible short of locking the wheels, while keeping steering movements very small. If the wheels lock, or you need a bigger steering correction, let off the brakes and then put them back on as soon as you can.

Answer

Hold the pedal down so the locked wheels scrub off speed

Answer

Turn the steering wheel sharply to break the wheels loose

Answer

Set the parking brake so it takes over from the service brakes

Question 11

The low air warning has just come on, and the needle keeps dropping. How long can you count on making a controlled stop with the brake pedal?

Accepted Answer

Only while enough air is left in the tanks to work the service brakes — You can only brake under control with the pedal while enough air remains in the tanks. Once pressure falls into the 20 to 45 psi range, the spring brakes come on. On a heavy load that can mean a very long stop, and on a light load or a slippery road it can mean a skid. That is why you stop and park as soon as the warning comes on.

Answer

Until the needle reaches zero, since the springs take over gradually

Answer

For as long as the engine keeps running

Answer

For about ten more brake applications, however low the pressure gets

Iowa CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. In a truck with a dual air brake system, the low air light and buzzer come on. One gauge still reads 110 psi while the other is falling. What should you do?

2. On Iowa's inspection test, you check the air lines between the power unit and an air-braked trailer. What does the manual say a low air condition can do to the trailer?

3. What is the key difference between the controlled braking and stab braking methods for an emergency stop?

4. Braking hard on ice in a truck without ABS, you lock up the front steering wheels. What is the immediate result?

5. While you're driving, a mechanical arm suddenly swings down into your view. What has happened?

6. You use stab braking in an emergency and notice the rig is not straightening out between applications. What is the most likely mistake?

7. A brake line on the primary side of your dual air brake system bursts, and that side loses its air. Why does the secondary side keep its pressure?

8. Glancing in your left mirror on the highway, you see a yellow lamp lit on the left side of your trailer. What is it most likely telling you?

9. Your straight truck has ABS on all axles, but its yellow ABS lamp has stayed lit all day. A car stops suddenly ahead and you must brake hard. Which approach fits the manual?

10. You're using controlled braking in an emergency in a truck without ABS, and the wheels lock. What does the manual tell you to do?

11. The low air warning has just come on, and the needle keeps dropping. How long can you count on making a controlled stop with the brake pedal?

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