How should the engineer notify the Trainmaster after securing a signal's stop arm?

The engineer should notify the Trainmaster immediately, upon securing the signal's stop arm because this action is critical in maintaining communication and safety protocols. Prompt notification ensures that the Trainmaster is aware of the situation in real-time, allowing for effective coordination and response to any potential issues that may arise from the signal being secured.

This immediate communication is essential for maintaining the integrity of operations and ensuring that all personnel are informed of the current status of the signal, especially in scenarios where it may affect train movements. Timely reporting is a key component of safe rail operations, as it allows for necessary adjustments to be made without delay, minimizing risks on the railways.

In contrast, options like notifying through a written report or at the end of the shift would introduce unnecessary delays, which could increase the risk of miscommunication or operational errors. Verbal notification via the radio may be prompt, but timing the notification to be immediately after securing the stop arm is crucial for the most effective communication.