What is the first action taken when the automatic HO is applied during inbound train inspection?

When the automatic handle on the brake system (referred to as the "HO") is applied during an inbound train inspection, the first action taken is to reduce the brake pipe to zero. This action is crucial as it initiates the braking process by allowing the brakes to fully engage. Lowering the brake pipe pressure to zero ensures that all the cars in the train respond appropriately by applying their brakes due to the pressure change.

This procedure is essential for safely inspecting the train, as it enables the crew to assess the effectiveness of the train's braking system. It is an established protocol within the rail industry to ensure that the train is properly secured before performing further actions such as securing hand brakes or notifying the dispatcher. By first reducing the brake pipe to zero, the crew ensures they are following the correct safety procedures that are fundamental to maintaining operational safety during the inspection process.