What must be issued by the controller if holding instructions have been issued and a delay is expected?

The correct response indicates that when holding instructions are already in place and a delay is anticipated, the controller must issue an Estimated Further Clearance (EFC). This is essential for maintaining efficient air traffic management and providing pilots with updated information regarding their expected departure from holding patterns.

The EFC informs the pilot when they can expect to leave the holding pattern, allowing them to manage fuel and other operational considerations effectively. It enhances situational awareness both for the pilots and the air traffic controllers, ensuring that everyone involved is aligned on expectations during uncertain periods.

Other options do not fit the scenario as directly. For instance, final routing clearance would be appropriate when the aircraft is ready to move from its holding pattern to its destination, but it does not address the immediate need for an updated schedule during a delay. An approach clearance pertains to the authorization for an aircraft to start its descent toward the airport, which isn't relevant during holding. New holding instructions would likely be unnecessary when an EFC can provide the required clarity on when the aircraft will be able to leave the hold.