Final answer:
The PFD ND has two submodes: the map mode, which displays a real-time, top-down view of the aircraft's route and surroundings during flight, and the plan mode, which is used for pre-flight planning with a simplified overview of the planned route.
Step-by-step explanation:
The Primary Flight Display's Navigation Display (PFD ND) typically has two submodes to provide pilots with essential navigational information. These submodes are known as the map mode and the plan mode.
The map mode is often used for the actual real-time navigation during flight, showing an aircraft-centric, top-down view of the aircraft's surroundings. It includes information such as the aircraft's current position, planned route, waypoints, air traffic, and weather data.
Plan mode, on the other hand, is normally used for pre-flight planning or while on the ground. It displays a simplified version of the route, helping pilots to get an overview and brief themselves on the planned journey.