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Alaska Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Alaska Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Alaska Division of Motor Vehicles. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.
Question 1 of 25
Brake fade is most likely caused by:
  • A Worn-out hoses
  • B Too much air pressure
  • C Cold weather
  • D Heat from continuous brake use on long downgrades
Correct answer: D
Heat reduces friction and brake effectiveness. Use a low gear so the engine, not the service brakes, holds the load.
Question 2 of 25
Front-wheel brakes are required on commercial vehicles because:
  • A They reduce stopping distance significantly without normally causing skids on dry pavement
  • B Federal law mandates them as decorative
  • C They look balanced
  • D They make steering easier
Correct answer: A
Front brakes provide a large share of stopping force and modern vehicles are designed so they do not cause front-wheel skids on dry pavement.
Question 3 of 25
A common cause of an air-brake skid is:
  • A Locking the wheels by braking too hard
  • B Both of the above
  • C Driving too fast for conditions
  • D Neither of the above
Correct answer: B
Skids result when the wheel locks and the tire loses traction. Speed and over-application are both common contributors.
Question 4 of 25
Slack adjusters should be checked because:
  • A They control trailer height
  • B Out-of-adjustment slack adjusters can result in brakes that do not work properly
  • C They affect engine performance
  • D They are decorative
Correct answer: B
Slack adjusters convert pushrod motion into braking force. Out-of-adjustment slack adjusters reduce braking ability and are a common out-of-service item.
Question 5 of 25
Spring brakes are held off by:
  • A Electrical current
  • B Hydraulic pressure
  • C Engine vacuum
  • D Air pressure
Correct answer: D
Compressed air holds the springs back. When air pressure drops, the springs apply the brakes mechanically.
Question 6 of 25
You should NOT drain the wet tank when:
  • A There is no situation in which draining is wrong
  • B It is full of moisture
  • C You are about to begin a trip
  • D The vehicle is in motion
Correct answer: A
Daily draining is a routine task; there is no situation where draining is unsafe (other than while driving).
Question 7 of 25
When testing low-air warning, you should:
  • A Look at the dashboard light
  • B Disconnect the trailer
  • C Pump the brake to fan down the pressure and verify the warning activates before pressure drops below 60 psi
  • D Drain the wet tank only
Correct answer: C
Fan the brakes (engine off) until the warning device activates and confirm it is above 60 psi.
Question 8 of 25
The proper braking technique on a long downgrade is:
  • A Apply the parking brake
  • B Light, intermittent braking with engine braking and a low gear
  • C Coast in neutral
  • D Heavy continuous braking
Correct answer: B
Use the proper low gear so engine braking does most of the work; brief, moderate brake applications keep the speed in check.
Question 9 of 25
A driver should never:
  • A Drain the wet tank
  • B Test the parking brake
  • C Make pre-trip inspections
  • D Use the trailer hand valve as a parking brake
Correct answer: D
The trailer hand valve is not a parking device — see the trailer-hand-valve question. Always set the trailer parking brakes.
Question 10 of 25
Each axle group on an air-brake-equipped vehicle has its own:
  • A Drive shaft
  • B Set of brake chambers
  • C Air compressor
  • D Engine
Correct answer: B
Each axle group has its own brake chambers fed by the air system; one compressor supplies all of them.
Question 11 of 25
Brake drums in good condition will:
  • A Be coated with oil
  • B Have small cracks
  • C Be glowing red after stops
  • D Be free of cracks longer than half the width of the friction area
Correct answer: D
Cracks longer than half the friction area or any visible heat checks usually fail inspection.
Question 12 of 25
The air compressor governor controls:
  • A When the air compressor will pump air into the storage tanks
  • B Coolant temperature
  • C Brake pad wear
  • D Engine RPM
Correct answer: A
The governor cuts the compressor in (start pumping) at low pressure and cuts it out (stop pumping) at high pressure to maintain a working range.
Question 13 of 25
You should test the parking brake by:
  • A Setting the parking brake, releasing the service brake, and gently trying to move the vehicle
  • B Doing nothing — the dashboard light is enough
  • C Driving over a curb
  • D Pressing the service brake while parked
Correct answer: A
Apply throttle gently in low gear; if the truck moves, the parking brake is not holding.
Question 14 of 25
The air-brake hand valve (trolley valve) operates:
  • A The tractor service brakes only
  • B Both tractor and trailer brakes
  • C The trailer service brakes only
  • D The parking brake
Correct answer: C
The hand valve applies only the trailer service brakes. It is not a parking brake or a substitute for the foot brake.
Question 15 of 25
You should test the trailer service brakes by:
  • A Listening for a hiss
  • B Pumping them while parked
  • C Looking at the gauge
  • D Releasing the parking brakes, moving the vehicle slowly forward, and applying the trailer hand valve
Correct answer: D
A low-speed pull-and-stop with the trailer hand valve confirms the trailer brakes apply on their own.
Question 16 of 25
You should test the service brakes by:
  • A Pumping the brakes
  • B At about 5 mph, applying the brake firmly and feeling for pulling, sticking, or unusual feel
  • C Listening to the air gauge
  • D Driving at 30 mph and slamming on the brakes
Correct answer: B
A low-speed brake test catches sticking, pulling, or weak brakes before you build up speed.
Question 17 of 25
A common practice during a long brake-recharge wait is to:
  • A Check the brake light visibility
  • B Drain the wet tank
  • C Disable the warning lamp
  • D Allow the system to reach operating pressure before driving
Correct answer: D
Always wait for full operating pressure (typically around 120 psi) before moving the vehicle.
Question 18 of 25
Modulating valves on the rear axle help prevent:
  • A Steering wander
  • B Tire blowouts
  • C Engine overheating
  • D Wheel lockup during emergency braking
Correct answer: D
Modulating valves and ABS sensors release pressure briefly to keep wheels from locking.
Question 19 of 25
If air pressure drops in the emergency line:
  • A Nothing happens
  • B Trailer spring brakes apply automatically
  • C Tractor brakes apply
  • D Trailer service brakes apply
Correct answer: B
Loss of supply-line pressure is the failsafe that triggers the trailer's spring brakes.
Question 20 of 25
When applying brakes in an emergency without ABS:
  • A Pump rapidly and lightly
  • B Use only the parking brake
  • C Use stab braking — apply hard, release when wheels lock, re-apply
  • D Press as hard as possible and hold
Correct answer: C
Stab braking keeps the truck straight in an emergency without ABS. Hard continuous pressure can lock the wheels and cause a jackknife.
Question 21 of 25
Anti-lock braking systems (ABS) on air-brake vehicles:
  • A Are required only on hazmat trailers
  • B Are optional and rarely installed
  • C Help prevent wheel lockup but do not necessarily shorten stopping distance
  • D Replace foundation brakes
Correct answer: C
ABS helps the driver maintain steering control by preventing wheel lockup. It does not necessarily reduce stopping distance.
Question 22 of 25
Stopping a vehicle with an air-brake failure can sometimes be done by:
  • A Coasting in neutral
  • B Honking
  • C Putting the transmission in reverse
  • D Using the trailer hand valve, then engine braking, then a runaway ramp if needed
Correct answer: D
In an air-brake failure, the trailer hand valve can still apply the trailer service brakes, then engine braking and a runaway ramp.
Question 23 of 25
A brake check ahead of a downgrade should be done:
  • A At the bottom only
  • B In the middle of the descent
  • C Once a year
  • D Before reaching the top, while still on level ground
Correct answer: D
A brief brake test on level ground at the top reveals problems while you can still stop safely.
Question 24 of 25
When applying brakes in an emergency with ABS:
  • A Stab the brakes
  • B Release the brakes immediately
  • C Pump rapidly
  • D Press as hard as possible and hold
Correct answer: D
With ABS, full pressure works because the system pulses for you, allowing maximum braking while preserving steering.
Question 25 of 25
You should not over-tighten a glad-hand because:
  • A It is bad luck
  • B It will reduce engine power
  • C It can damage the rubber seals
  • D It violates federal weight law
Correct answer: C
Over-tightening crushes the seals. The connection should be firm but not forced.

Study tips for the Alaska Air Brakes exam

The Air Brakes portion of the Alaska CDL exam is graded out of the bank of questions the Alaska Division of Motor Vehicles draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Alaska CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Alaska handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Air Brakes.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Alaska Division of Motor Vehicles will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Air Brakes exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Alaska General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Air Brakes study guide and the matching chapter in the official Alaska CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Alaska Division of Motor Vehicles office.

Already comfortable with this endorsement? Drill another: AK General Knowledge · AK Combination Vehicles · AK Hazardous Materials · AK Passenger · AK School Bus · AK Tank Vehicle · AK Doubles / Triples

New to the CDL process in Alaska? Read How to apply for a CDL in Alaska for the document checklist and step-by-step timeline.