What should be observed when the engine is idling during an air brake system inspection?

When conducting an air brake system inspection with the engine idling, it is essential to observe the pressure drop in psi per minute with the brakes fully released. This measurement is critical because it allows the inspector to assess whether the air brake system maintains adequate pressure. A significant drop in pressure while the brakes are not applied may indicate a leak or malfunction in the air brake system, which could compromise safety during vehicle operation.

By monitoring this pressure drop, inspectors can determine the integrity of the air system. A healthy system will show minimal to no pressure loss; if there is a notable decrease, it signals the need for further investigation or repairs.

Other aspects like the pressure drop with brakes applied, the governor cut-out pressure, or the time it takes to build pressure are also important, but they address different functions or phases of the air brake system's operation. For instance, measuring the drop with brakes applied focuses on how well the system holds pressure under load, while governor cut-out pressure and build time measurements are relevant to the system's performance rather than the immediate leak detection capability when idling.