What flight plan number is always shown as the active flight plan?

The active flight plan in aviation systems is typically denoted as FP 0. This notation indicates the primary or active flight plan that the aircraft is currently utilizing during its operation. The designation FP 0 is a standard convention used in many avionics systems, ensuring clarity and consistency for pilots and air traffic control.

In contrast, other flight plan numbers, such as FP 1, FP A, or FP ACTIVE, may refer to alternate or secondary flight plans, which are not currently in use but can be activated as needed. It's crucial for pilots to recognize that only one flight plan can be active at a time, which is why FP 0 serves as the primary reference point for navigation and operation during a flight. Understanding this terminology is vital for effective communication and operational safety in flight planning and execution.