Once the trailer is coupled to the tractor, what is essential to check about the connection?

In the context of coupling a trailer to a tractor, ensuring that the trailer is securely coupled and locked is crucial for safety and operational integrity. If the trailer is not properly attached, it can lead to a disconnection while driving, which poses significant risks such as loss of control, accidents, or damage to both the tractor and trailer.

While checking other aspects, such as the trailer lights functioning and the landing gear being fully extended, are important for overall vehicle safety and readiness, they do not directly address the core concern of the trailer's secure attachment. Similarly, confirming that the tractor is in neutral is vital for safe operation but does not relate to the physical connection between tractor and trailer. Therefore, ensuring the trailer is securely coupled and locked is the most critical check to perform immediately after coupling.