What is one of the main purposes of releasing the master controller handle during a brake test?

Releasing the master controller handle during a brake test is primarily aimed at testing the operation of the dead-man feature. This feature is a crucial safety mechanism designed to ensure that the train operator is actively controlling the train. If the operator becomes incapacitated or fails to maintain control for any reason, releasing the master controller handle triggers an emergency brake application. This ensures that the train will come to a stop in a controlled manner, thereby preventing potential accidents.

The dead-man feature is essential for maintaining safety standards during train operations, making it vital for operators to verify that this mechanism functions correctly during routine checks such as brake tests. By confirming that the dead-man feature engages the brakes when the handle is released, operators can ensure their responsibilities for safety are met before proceeding with the operation of the train.