Mississippi CDL — Air Brakes practice
Mississippi CDL — Air Brakes: Handling Emergencies practice test
What to do when things go wrong — brake failure, tire blowouts, skids, and stalling on railroad tracks.
Content reviewed against official driver handbooks · August 12, 2026
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9 sample Handling Emergencies questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.
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1. If the low air warning signal does not work, what could happen in a single-circuit air brake system?
Correct answer: You could lose air pressure without knowing it and get sudden emergency braking
Without a working warning you may not notice falling pressure. In a single-circuit system that can mean sudden emergency braking; in a dual system it means a longer stopping distance.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Final Air Brake Check)
2. In stop-and-go traffic you keep pressing and releasing the brake pedal far more than you need to. What could this lead to?
Correct answer: Air leaving the system faster than the compressor can replace it, until the brakes no longer work
Each time you release the pedal, some compressed air is let out and the compressor has to make it up. Needless fanning can drain pressure faster than it is rebuilt, and with too little pressure the brakes stop working.
Source: Mississippi CDL Manual — Section 5: Air Brakes (The Brake Pedal)
3. Your truck has a brake system failure. To bring it to a stop, the emergency brake system relies on parts of which other systems?
Correct answer: The service brake and parking brake systems
There is no fully separate emergency brake. When something fails, the emergency system borrows components from the service brakes and the parking brakes to stop the vehicle.
Source: Mississippi CDL Manual — Section 5: Air Brakes
4. If your service brakes fail, how can a modulating control valve help you stop?
Correct answer: It lets you apply the spring brakes gradually, harder the farther you move the lever
A modulating valve is a spring-loaded dash handle that gives you a feel for braking. The more you move it, the harder the spring brakes apply, so you can control them when the service brakes are gone.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Parking Brake Controls)
5. Your truck is nearly empty and the road is wet when a leak drains the air system and the spring brakes come on. What does the manual warn could happen?
Correct answer: The vehicle may skid out of control
When spring brakes apply on a lightly loaded vehicle or a slippery road, the vehicle can skid out of control. Stopping while you still have air for the foot brake is much safer.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Low Air Pressure)
6. During controlled braking in an emergency, how should you handle the steering wheel while the brakes are applied?
Correct answer: Keep steering movements very small
Controlled braking means applying the brakes hard while stopping short of wheel lockup, with only small steering inputs. A bigger correction calls for releasing the brakes first.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Emergency Stops)
7. Braking hard on a slick road in a vehicle without ABS, you lock the rear wheels but not the steering wheels. What is the main danger?
Correct answer: A skid, a jackknife, or even a spin
Locked steering wheels take away your steering. Locking the other wheels brings a different risk: the vehicle may skid, jackknife, or spin.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Braking with Antilock Brakes)
8. A manual-reset wig wag has dropped into your view. When can you move it back out of view and have it stay there?
Correct answer: Only once system pressure is back above 55 psi
An automatic wig wag lifts away by itself when pressure recovers. The manual-reset type has to be put back by hand, and it will not stay up until pressure is above 55 psi.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Low Air Pressure Warning)
9. On some older air-braked vehicles, the visible low air warning is not tied to 55 psi. What is it based on instead?
Correct answer: One half of the compressor governor's cut-out pressure
A visible warning has to come on before tank pressure falls under 55 psi. On older vehicles the trigger may instead be half of the governor cut-out pressure.
Source: Mississippi CDL Manual — Section 5: Air Brakes (Low Air Pressure Warning)
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