At what point should an operator lower the trailer's landing gear during uncoupling procedures?

Answer: B — After placing chock blocks

Lowering the trailer's landing gear after placing chock blocks is essential for ensuring safety during uncoupling procedures. When the chock blocks are in place, they prevent the trailer from rolling or shifting, providing a stable support system. This step is crucial because it helps secure the trailer in position before any further actions are taken, such as disconnecting the air lines or completely uncoupling the trailer from the tractor. By lowering the landing gear after placing the chocks, the operator also helps to distribute the trailer's weight properly and minimizes the risk of injury or accidents caused by unexpected movement. Therefore, this practice demonstrates adherence to safety protocols, ensuring both the operator and equipment remain protected during the uncoupling process.