Before backing under a trailer, which safety check is necessary?

Ensuring that the trailer brakes are locked is a critical safety check before backing under a trailer. This step is essential because locked brakes prevent the trailer from rolling away unexpectedly while the tractor is being backed into position. If the trailer brakes are not locked, there is a risk of the trailer moving, which can lead to accidents, damage to equipment, or injury to personnel.

By confirming that the trailer brakes are locked, the driver can safely position their tractor under the trailer without the concern of the trailer rolling or shifting. This precaution helps maintain control during the coupling process and contributes to overall safety when working with heavy equipment.

Other checks, while important, do not address the immediate risk of trailer movement. Checking air supply knobs or confirming air brakes are off relates to the functioning of the braking system but does not provide the same level of safety as ensuring the brakes are locked in place before backing. Similarly, verifying the cargo load is critical for operational and safety reasons but does not directly affect the current process of backing under the trailer.