What must the air pressure be above to perform the low-air warning system procedure?

To perform the low-air warning system procedure, the air pressure must be above 90 psi. This threshold is critical because it ensures that the air brake system is functioning properly and that the vehicle is in a safe operating condition. At pressures above 90 psi, the low-air warning devices can be accurately checked, confirming that they will alert the driver if air pressure drops to a level that could compromise the braking system.

Maintaining air pressure above this level is essential because the air brake system relies on compressed air to operate effectively. If the pressure falls below this level, it could lead to a loss of braking capability or insufficient power to activate warning signals, creating a dangerous situation. Thus, ensuring the air pressure is adequately high not only helps in maintaining effective control over the vehicle but also plays a crucial role in the overall safety of the operation.