Final answer:
When a train operator must pull an emergency brake, they must immediately notify the train dispatcher or control center to ensure passenger and train safety.
Step-by-step explanation:
When it is necessary for a train operator to pull an emergency brake, the rules state that he MUST then immediately notify the train dispatcher or control center.
Notifying the dispatcher or control center is crucial because it allows them to take appropriate action to ensure the safety of passengers and other trains on the track.
By promptly notifying the dispatcher, train operators can help prevent potential accidents or collisions and ensure a quick response from the relevant authorities.