What is the correct action when stopping a train upon flagging?

When flagging a train, turning the mode selector switch to MCS (Manual Control System) and manually stopping the train is the appropriate action. This method allows the operator to have greater control over the train's speed and stopping distance, which is crucial in situations where there are flaggers or track hazards present.

Using manual control helps to ensure that the train comes to a complete stop in a safe manner, allowing the flaggers to do their work without the risk of the train continuing to move unexpectedly. This level of control is fundamental when following safety protocols designed to protect both railway personnel and equipment.

Other actions, such as applying emergency brakes immediately, could lead to abrupt stops that might not be safe or necessary and could potentially cause derailment or injury. Continuing to operate without modification does not consider the safety risks involved with flagging, and notifying Control before stopping may be part of the procedure but does not address the immediate need to manually stop the train. Therefore, using the MCS for a manual stop is the most effective and safe course of action in this scenario.