School Bus With Air Brake Leak, ABS Warning and Cracked Disc

The static pressure drop is 1.4 bar over 2 minutes, or about 0.7 bar per minute. That is well above the normal acceptance limit for a charged air brake system with the engine off, which is typically a small fraction of a bar per minute depending on the manufacturer's specification. A leak of this rate means the compressor must work harder, the system may not maintain sufficient reserve pressure during repeated brake applications, and a low-pressure warning or emergency brake application could occur on a long descent. The "long" pedal on first application is consistent with lost air volume or a leaking circuit.

The ABS warning lamp remaining on after the self-test indicates that the ABS is not functioning or has a stored fault. ABS is not usually the primary service brake, but on a school bus on steep descents it is an important stability aid, especially in wet conditions. A vehicle with a known air leak, an ABS fault and contaminated or cracked brakes should be treated as unroadworthy. The examiner should not continue with a brake performance test that could be unsafe; the vehicle should be failed and taken out of service until repaired.

The cracked front brake disc extending to the hub is a dangerous defect. A disc crack can propagate under heat and load and lead to wheel-end brake failure. Oil contamination on the rear linings is also dangerous or at least major, because oil reduces friction and can cause uneven braking or pulling; linings normally must be replaced rather than cleaned. The air leak is a major defect because it affects the service brake system's ability to maintain pressure. The ABS warning is a major defect because a required safety system is not functioning.

The request for a "pass with a note" cannot be granted. A note does not make an unroadworthy school bus safe, and allowing it to continue in passenger service until the weekend would expose the driver, passengers and other road users to an unacceptable risk. The examiner should fail the vehicle, record the defects, and advise that it must be repaired and re-examined before further use. If the vehicle is at the centre, it should not be driven away in a dangerous condition; the owner should arrange recovery or repair on site. The examiner should not allow commercial pressure or the age of the vehicle to soften a safety-critical decision.

The record should state the initial and final air pressure, the time interval and the calculated leak rate, the ABS lamp status before and after the self-test, and the driver's complaint about the pedal. It should describe the oil contamination on the rear linings and the location and extent of the crack in the front left disc, with photographs if permitted. The examination result should be recorded as a fail, with each defect classified according to the centre's scheme. The owner's request for a pass with a note and the examiner's refusal should be recorded factually, including the reason: passenger-carrying school bus on steep descents with safety-critical brake defects.

The owner should receive clear written advice that the bus must not be used until the air leak is repaired, the ABS fault is rectified, the contaminated linings are replaced and the cracked disc is replaced. The examiner should explain that re-examination is required and that the vehicle may need to be transported rather than driven. Any request to delay repair should be declined. If the operator persists, the examiner should escalate to the centre supervisor and, where appropriate, report the vehicle as unroadworthy through the established enforcement channel. The communication should be firm, factual and consistent with the recorded defects.