When should you not back a tractor under a trailer?

Backing a tractor under a trailer should not occur when the whole air system is not at normal pressure. This is critical because the air brake system relies on proper pressure to function effectively. If the air system is not at its normal pressure, the trailer's brakes may not be fully released or may engage unexpectedly, leading to a dangerous situation during the backing process.

Furthermore, it ensures that the suspension system, which is often air-operated, is also functioning correctly, allowing for proper alignment and connection between the tractor and trailer. A malfunction in the air system can compromise the safety of the vehicle operation, making it essential to ensure that the air pressure is at the correct level before attempting to back the tractor under the trailer.

This emphasizes the importance of a thorough pre-trip inspection, focusing not only on visual checks but also on system pressures and functionalities to ensure safe operation.