Which mode should be set before coupling for the aiding train in Brake Pipe procedures?

Setting the mode to Brake Pipe (BP Mode) is essential for the proper coupling of the aiding train in Brake Pipe procedures. This mode ensures that the train’s braking system is correctly configured to allow for safe and effective integration with another train.

BP Mode establishes the critical communications between the brake systems of the two trains, facilitating the sharing of brake pressure information necessary for coordinated braking operations. It also ensures that any safety mechanisms designed to prevent premature or incorrect coupling are active, reducing the risk of accidents during the coupling process.

In this context, the other modes serve different purposes that are not suitable at the coupling stage. Display mode primarily shows information but does not allow for necessary adjustments to the braking system. Emergency mode would trigger safety protocols that could prevent successful coupling, and isolation mode disconnects the train's braking system, which would be counterproductive during the coupling process. Thus, BP Mode is the appropriate setting to ensure a successful and safe coupling.