Which action must be taken to ensure that incoming message traffic of all priority levels will be received through Inmarsat-C?

To ensure that incoming message traffic of all priority levels will be received through Inmarsat-C, it is essential for the GMDSS Radio Operator to log in to the desired satellite, especially if the unit has not automatically established a connection. Each Inmarsat-C terminal operates by establishing a communication link with a specific satellite, which is necessary to receive messages.

When the operator logs in to the satellite manually, it guarantees that the terminal is properly registered with the Land Earth Station (LES) that facilitates communication. This action ensures that the terminal can receive all the traffic directed to it, including distress, urgency, and safety messages.

In contrast, if the satellite connection is not established—either through automation failure or other issues—the terminal may not receive important incoming messages. This makes the logging-in process a critical step for reliable message reception.

While the other options mention various aspects of operation, they do not guarantee connection to the satellite, which is the key factor for receiving all incoming messages effectively. A simple power on or commissioning of the system does not automatically ensure that it is logged into the correct satellite. Therefore, logging in is a necessary action for complete communication capability through Inmarsat-C.