What is the first step to conduct an air test after adding helpers to the rear of a train?

The first step to conduct an air test after adding helpers to the rear of a train is to increase the brake pipe reduction by at least 8 psi. This increase is necessary to ensure that the entire train, including the newly added helper units, is properly engaged in the air brake system. By making this reduction, the engineer ensures that there is a sufficient pressure drop in the brake pipe, which allows the air brakes on the helper locomotives to begin applying effectively.

This step is fundamental because it establishes the conditions required for a successful diagnostic test of the air brake system. It allows for confirming that all units in the train are responsive to the changes made in the brake pipe pressure, which is critical for safe train operations, particularly with the additional weight and dynamic behavior introduced by the helpers.

While releasing and recharging the brake system is important for ensuring the train's air systems are properly functioning, it typically happens after the initial pressure adjustments. Observing the brake application on the helper consist is a subsequent step that relies on prior conditions being met, and determining the brake pipe increase at the rear of the train comes after the initial pressure reduction is made.