To avoid shock loading before a coupling is made, what must the RCO do?

To avoid shock loading before a coupling is made, moving the speed selector from the couple to the stop position is vital. This action ensures that the system comes to a complete stop before the coupling process begins. Shock loading can occur when sudden changes in velocity or torque are introduced to mechanical systems, potentially leading to damage or failure. By stopping the system completely, the RCO can smoothly engage the coupling without applying unexpected forces, thereby safeguarding both the equipment and the operation.

Other options may not effectively prevent shock loading. For instance, gradually increasing the speed is generally used to ensure smooth acceleration, but it doesn't address the immediate requirement of stopping movement before coupling. Engaging a pitch button or a manual override might adjust other parameters or modes but does not directly mitigate the risk of sudden mechanical stresses during the coupling process. Thus, correctly placing the speed selector in the stop position is the most effective and appropriate action in this scenario.