Air Brake Inspections

Air Brake Inspections are the most important component of a Pretrip Inspection, and must be performed before a vehicle can be put into service.

Brake checks are noted on the Vehicle Inspection Report using the acronym COLAS, with each letter standing for a different brake check. In addition to COLAS, two additional tests must be performed.

If a vehicle fails one of the airbrake checks, it is possible to re-test. However, if a bus fails a test several times, inform base. If a bus fails an air brake inspection, it cannot go on route without explicit permission from a supervisor.

Note that Air Brake Inspections are only necessary for vehicles with air brakes. Cutaways, trucks, vans and other vehicles without air brakes have a different brake check procedure.

Cut-In Test (C)
The Cut-In test evaluates whether the vehicle's compressor governor can activate at the appropriate time.

Conditions: Bus must be running.

With the bus running, apply the brake firmly, once. Make sure that the pressure does not go below 85 psi.

The test is successful if/when you witness a gradual increase in air pressure.

During the test, DO NOT fan the brakes (apply them more than once, or quickly in succession). This constitutes an automatic failure.

Note: some buses may take time to build pressure, especially after sitting all night. Generally three minutes without an increase in pressure is considered the limit before the bus has "failed" the Cut-In Test, though there is technically no formal time limit.

Cut-Out Test (O)
The Cut-Out test evaluates whether the vehicle's compressor governor can shut off the compressor once air has reached an appropriate pressure.

Conditions: Bus must be running.

With the bus running, simply apply the brakes to reduce the pressure below ~100 psi. Wait for a gradual increase in pressure, then, ensure that the pressure stops rising at no greater than 130 psi.

If the pressure rises above 130 psi, the bus has failed the test. Remember: at 150 psi, the emergency air release valve will activate.

Low Air Warning (L)
The Low Air Warning test evaluates whether the bus can present the appropriate dashboard warning light and audible warning in the event of low air pressure.

Conditions: Bus must be on.

Apply the brakes and decrease the pressure. Listen for both a visual and audible warning between 55-75 psi. The bus must present both a visible and audible warning between 55-75 psi.

Applied Air Loss Test (A)
The Applied Air Loss Test evaluates whether there are leaks or other problems which cause a significant loss of pressure over time.

Conditions: Bus not running, parking brake disengaged , doors closed.

Press and hold the brakes down for a period of 60 seconds. (Use a stopwatch or timer, do not simply wait for a minute to pass on syncromatics). The bus cannot lose more than 3 psi in 60 seconds.

Spring Brake Test (S)
In the event of total air loss, the spring brakes on the bus should activate and stop the bus immediately.

Conditions: Parking brake disengaged

Pump the brakes slowly but continuously to lower the air pressure, waiting for needles to stabilize before pumping again. The spring brake should activate automatically between 25-45 psi.

Service Brake Check
The Service Brake Check evaluates whether the brakes can slow and stop the bus smoothly when in motion.

Simply roll forward at a low speed and apply the brakes. Listen for any unusual grinding, pulling to one side, or other abnormalities.

Parking Brake Check
Put the bus into Drive, and pull out the parking brake. '''Use the accelerator to rev the engine to ~1500 RPM. The bus should not move.'''

Trivia
Despite the order of the acronym COLAS, it is more common to perform the Low Air and Spring Brake tests together, meaning that in order of performance, the tests are:
 * ACOLS
 * COLSA
 * COALS