What position should the cutout valve be in on the controlling locomotive?

The cutout valve on the controlling locomotive plays a crucial role in the operation of the air brake system. In the context of air braking systems, the term "FRT/IN" refers to the designations used for the position of the cutout valve—meaning that the valve is set to allow the flow of air for the brakes to function properly.

When the cutout valve is in the FRT/IN position, it indicates that the brakes on the controlling unit are fully operational, allowing for efficient engagement of the braking system when needed. For safety and functionality, ensuring that the cutout valve is in this position enables the locomotive to effectively manage air pressure and brake application across the train.

In contrast, the other positions, like "Open," "Closed," or "Out," would not support the proper functioning of the air brake system, potentially leading to issues with effective train braking or air distribution. Therefore, having the cutout valve set to FRT/IN is essential for optimal braking performance and operational safety.