Maine CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

The parts descriptions in the Air Brakes section name several things that can leave you with brakes that do not work. Which of these is NOT one of them?

Accepted Answer

Leaving a front brake control in the 'normal' position — The manual warns that ice in the system can stop the brakes from working, that too much heat can do the same, and that the brakes won't work once pressure gets too low. The 'normal' position on an older front brake control is the one it recommends, because it gives normal stopping power.

Answer

Ice forming inside the air system

Answer

Too much heat in the brake drums

Answer

Tank pressure dropping too low from needless pedal use

Question 2

A major leak has pulled your straight truck's air pressure down to 40 psi, and it is still falling. What should you expect from the spring brakes at this point?

Accepted Answer

They could be coming on, since they apply fully somewhere between 20 and 45 psi — Spring brakes on tractors and straight trucks come fully on once pressure falls to anywhere from 20 to 45 psi. That is why the manual tells you to stop when the low air warning first comes on, while you still control the brakes.

Answer

Nothing, because spring brakes stay off until the tanks are completely empty

Answer

Nothing, because spring brakes apply only when the driver pulls the knob

Answer

They will release, since low pressure lets the springs relax

Question 3

Maine's inspection test section explains why the air lines running from the power unit to the trailer matter. What does it say losing the air supply to the trailer will lead to?

Accepted Answer

The towed unit loses some or all of its braking — For air brakes, the manual says that when air to the trailer is lost, braking on the towed unit is partly or completely gone. It adds that a low air condition can make the trailer's spring brakes apply suddenly.

Answer

The trailer brakes harder than the tractor does

Answer

The tractor's ABS lamp switches off

Answer

The governor raises its cut-out pressure

Question 4

A diagram in the manual's Air Brakes section describes the tractor protection valve. According to it, what does the valve do if the air supply drops while you are driving?

Accepted Answer

It closes automatically — The diagram notes that the tractor protection valve provides the air supply and closes on its own if that supply drops during driving. It also shows that applying the parking brakes closes the valve and sets the spring brakes together.

Answer

It opens wider to send the trailer more air

Answer

It releases the spring brakes

Answer

It switches the compressor back on

Question 5

The manual warns about two different outcomes if you keep driving after a low air warning until the spring brakes come on by themselves. Which pairing is right?

Accepted Answer

Heavily loaded vehicle: a long stopping distance. Lightly loaded vehicle or slippery road: a possible skid out of control — Spring brakes act on only some of the axles, so a heavy vehicle needs a long distance to stop on them. A light vehicle, or any vehicle on a slick road, may skid out of control when they apply. Stopping with the foot brake while air remains is much safer.

Answer

Heavily loaded vehicle: a possible skid out of control. Lightly loaded vehicle: a long stopping distance

Answer

Heavily loaded vehicle: no effect. Lightly loaded vehicle: the brakes do not apply at all

Answer

Both: the stop is shorter than one made with the foot brake

Question 6

Which of these is NOT a step in the stab braking method?

Accepted Answer

Keep the pedal down through the lockup until the vehicle stops — Stab braking is a cycle: full brakes, release when the wheels lock, and full brakes again as soon as the wheels are rolling. Holding the pedal down through a lockup is not part of it.

Answer

Apply the brakes all the way

Answer

Let off the brakes when the wheels lock up

Answer

Brake fully again once the wheels start rolling

Question 7

You brake hard on a slippery road in a vehicle without ABS. Which pairing of locked wheels and result matches the manual?

Accepted Answer

Steering wheels lock: you lose steering control. Other wheels lock: you may skid, jackknife or spin — Locked steering wheels cost you steering control. When the other wheels lock, the vehicle may skid, jackknife, or even spin. ABS is there to help you avoid wheel lockup.

Answer

Steering wheels lock: the vehicle may jackknife. Other wheels lock: you lose steering control

Answer

Steering wheels lock: the stop gets shorter. Other wheels lock: nothing changes

Answer

Either set locks: the spring brakes apply

Question 8

Controlled braking and stab braking are different methods for an emergency stop. Which instruction do the two share?

Accepted Answer

Release the brakes if the wheels lock — In controlled braking you brake hard but try to stay short of lockup, and you let off if the wheels lock anyway. In stab braking you brake fully and let off when the wheels lock. Either way, locked wheels are the signal to release, and then you brake again.

Answer

Hold the pedal all the way down until the vehicle stops

Answer

Never put the brakes back on once you have released them

Answer

Make large steering movements while the brakes are applied

Question 9

The manual tells you to ease off the brakes if a trailer starts to swing out or a tractor jackknife begins. What condition does it attach to that advice each time?

Accepted Answer

Only when it is safe to do it — Each time the manual says to let up on or back off the brakes to regain control, it adds the same qualifier: do it if that can be done safely.

Answer

Only if the road is dry

Answer

Only if you are going under 25 mph

Answer

Only if the ABS lamp is lit

Question 10

You are driving a large bus, and the low air pressure warning comes on with the gauge showing about 82 psi. A trainee says the warning must be faulty because it is not due until 55 psi. What does the manual say?

Accepted Answer

Warning devices on large buses commonly signal at 80 to 85 psi — The 55 psi figure is the point a visible warning must come on before. The manual adds that on large buses the warning devices commonly signal at 80-85 psi, so a warning at that pressure is normal there.

Answer

The trainee is right, and the warning device needs repair

Answer

Bus warnings are set to come on only below 45 psi

Answer

A warning above 55 psi means the governor has failed

Maine CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. The parts descriptions in the Air Brakes section name several things that can leave you with brakes that do not work. Which of these is NOT one of them?

2. A major leak has pulled your straight truck's air pressure down to 40 psi, and it is still falling. What should you expect from the spring brakes at this point?

3. Maine's inspection test section explains why the air lines running from the power unit to the trailer matter. What does it say losing the air supply to the trailer will lead to?

4. A diagram in the manual's Air Brakes section describes the tractor protection valve. According to it, what does the valve do if the air supply drops while you are driving?

5. The manual warns about two different outcomes if you keep driving after a low air warning until the spring brakes come on by themselves. Which pairing is right?

6. Which of these is NOT a step in the stab braking method?

7. You brake hard on a slippery road in a vehicle without ABS. Which pairing of locked wheels and result matches the manual?

8. Controlled braking and stab braking are different methods for an emergency stop. Which instruction do the two share?

9. The manual tells you to ease off the brakes if a trailer starts to swing out or a tractor jackknife begins. What condition does it attach to that advice each time?

10. You are driving a large bus, and the low air pressure warning comes on with the gauge showing about 82 psi. A trainee says the warning must be faulty because it is not due until 55 psi. What does the manual say?

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