If the captain does not respond to the interphone, what is your first action?

The first action should be to try all interphones because ensuring communication is critical in aviation operations. If the captain does not respond, it is essential to check if the issue lies with the specific interphone being used or if the captain is unable to respond at all due to another reason. Trying all interphones allows the crew to confirm whether the communication failure is isolated or systemic. It also helps resolve any potential technical issues with a specific interphone, ensuring that lines of communication remain open and that the crew can obtain necessary information.

Following this assessment, other options such as notifying ground control or airport staff would be appropriate, but establishing direct communication is the priority to ascertain the situation accurately. Engaging passengers would not be an effective first response, as they are not equipped to handle cockpit communication issues. Therefore, the focus should be on attempting to restore communication with the captain as the immediate next step.