What must a pilot do if they do not depart within 30 minutes after their clearance void time?

If a pilot does not depart within 30 minutes after their clearance void time, they are required to notify Air Traffic Control (ATC). This is important because the clearance is no longer valid after the void time has passed, which means that the pilot cannot legally depart without re-establishing communication with ATC.

Notifying ATC allows the pilot to either request a new clearance or receive guidance on the next steps to take. This communication ensures that the air traffic system remains safe and organized, as ATC needs to manage traffic and routes based on the status of each aircraft. By informing ATC, the pilot helps maintain situational awareness and avoids potential conflicts with other aircraft.

In contrast, the other options do not adequately address the proper protocol following a void clearance. Reapplying for clearance without notifying ATC first may lead to confusion or mismanagement of air traffic. Returning to the departure airport may not be necessary or practical, and waiting for the next scheduled departure time does not address the need for communication and coordination with ATC.