What action must a pilot take if they deviate from an ATC clearance?

When a pilot deviates from an Air Traffic Control (ATC) clearance, they are required to notify ATC as soon as possible. This is essential for maintaining safety and situational awareness in the airspace system. By promptly informing ATC about the deviation, the pilot ensures that the control tower is aware of their current position and intent, allowing for appropriate traffic management.

Such notification helps prevent conflicts with other aircraft and allows ATC to provide any necessary assistance or guidance, potentially mitigating risks that arise from the deviation. Additionally, timely communication enables the controller to adjust the traffic flow as necessary, ensuring that all aircraft can operate safely and efficiently.

The other options do not align with standard operating procedures. For example, waiting for ATC to initiate contact could lead to misunderstandings or dangerous situations. Filing a report after landing is part of post-event procedures but does not address the immediate need for communication during the flight. Resuming clearance without making notification undermines safety and could lead to serious consequences if another aircraft is involved. Therefore, ensuring that ATC is promptly informed is critical in these situations.