Which action should be avoided when the train is struggling to maintain speed on a heavy grade?

Using the emergency brake as a first resort should be avoided when the train is struggling to maintain speed on a heavy grade because the emergency brake is intended for situations that require an immediate and drastic reduction in speed or to stop the train quickly. Engaging it prematurely can lead to unnecessary wear on the braking system, loss of control, and potential derailment, especially in a situation where a more measured response would be effective.

In scenarios where the train is challenged by a heavy grade, maintaining control and carefully managing speed are vital. Instead of opting for the emergency brake, operators should consider adjusting throttle settings, monitoring speed, and using gradual braking techniques to manage the situation effectively and safely. Employing these strategies helps in stabilizing the train's speed without resorting to extreme measures that could pose safety risks.