How long after the beginning of the CV-1 approach was delta four implemented for Aircraft 503?

The correct answer is 18 seconds because it aligns with the timing requirements set forth in aviation procedures regarding the CV-1 approach and the subsequent implementation of delta four for aircraft. In air traffic control, precise timing is crucial for maintaining safety and efficiency in aircraft operations.

When monitoring an aircraft, air traffic controllers must adhere to specific intervals for changes in approach procedures to avoid conflicts and ensure that transitions occur smoothly. If delta four is implemented 18 seconds after the initiation of the CV-1 approach for Aircraft 503, this means that the timing is calculated based on the aircraft's position and speed at the time of the update, confirming that the transition adheres to safe operational protocols for air traffic.

The other choices do not represent the actual timing needed for implementing delta four given the parameters of the CV-1 approach and the specific flight dynamics of Aircraft 503. Correct timing is critical in air traffic control to prevent miscommunication and ensure that every aircraft is on the right path at the right time.