What is required when helper locomotives are added to a train?

Answer: C — Class III Brake Test

When helper locomotives are added to a train, a Class III Brake Test is required. This type of brake test ensures that the emergency brakes of the entire train are functioning properly. It involves verifying that the train's air brake system operates effectively after the addition of the extra locomotives. The Class III Brake Test specifically focuses on ensuring that the brakes can be applied and released in a way that guarantees they will function correctly in the event that emergency brake application is needed. This requirement is in place to maintain safety standards, as adding locomotives to a train alters its dynamics and braking capabilities. Ensuring that the brakes work cohesively across the entire system is crucial to prevent accidents and ensure the stability of the train during operation. Thus, conducting a Class III Brake Test when helper locomotives are added provides a necessary safeguard for both the crew and the cargo being transported.