What type of brake application must accompany the PKO by-pass?

Answer: A — Emergency brake application

The proper brake application that must accompany the PKO (Power Key Off) by-pass is an emergency brake application. This requirement is in place to ensure safety during situations where the power to the train is being interrupted while in motion. An emergency brake application provides a controlled stop of the train, reducing the risk of accidents or uncontrolled movements. Implementing an emergency brake application ensures that the train can safely decelerate and come to a stop if necessary, particularly in scenarios where the train's systems could potentially fail or operate unpredictably due to the PKO by-pass. This measure is a critical safety protocol ensuring that operators can maintain control over the train during changes in brake system status.