When should you lower the landing gear when uncoupling a truck-tractor from a semi-trailer?

Lowering the landing gear before disconnecting the electrical and air lines is important for ensuring safety during the uncoupling process. By lowering the landing gear first, you provide stability to the semi-trailer, which helps prevent it from tipping or sliding away from the truck-tractor once the coupling connection is broken. This step is critical to maintain control over the trailer while you proceed with disconnecting the lines.

If the landing gear were to be lowered after disconnecting the lines, there is a risk that the trailer could shift unexpectedly, leading to potential hazards, such as falling or moving unexpectedly. The sequence of operations is designed to prioritize safety and maintain the integrity of the equipment throughout the process.