What must a crew do if a helper locomotive is added to a train?

When a helper locomotive is added to a train, it is essential for the crew to perform a Class 3 air brake test. This test ensures that the air brake system functions effectively with the combined force of the new locomotive and the existing train. The primary focus of the Class 3 air brake test is to verify that the air is charged throughout the entire system and that all components are working properly, which is crucial for the safety of the train operations.

Charging the air system alone does not confirm that the brakes are fully operational and responsive; therefore, it is insufficient as a standalone action when integrating a helper locomotive. Consulting a manual for guidelines could be helpful but does not directly address the immediate need for a safety test. Simply notifying the dispatcher is also not enough, as all safety checks must be completed before the train departs, ensuring that the crew is fully aware and confident in the train's braking capabilities. Thus, performing a Class 3 air brake test is the critical and necessary step when a helper locomotive is added.