What is the first step when disconnecting a semi-trailer from a tractor?

The first step when disconnecting a semi-trailer from a tractor is to ensure that the ground supports the trailer's weight. This is crucial because a properly supported trailer prevents it from rolling or tipping as it is disconnected from the tractor. When the trailer is placed on stable ground, it becomes safe to release the coupling mechanism and other connections without risking any movement that could lead to accidents or injuries.

Taking this step first safeguards both the loading area and the personnel involved in the disconnection process. It establishes a safe environment before any further actions are taken, ensuring that the trailer remains stable while you proceed with tasks such as lowering the landing gear, disconnecting air lines, and finally detaching the tractor from the trailer.