What is the primary purpose of a flight waypoint?

The primary purpose of a flight waypoint is to provide navigation reference points along the route. Waypoints are predefined geographical locations that pilots use to help navigate during a flight. These waypoints can serve as critical points for route planning and monitoring, allowing pilots to follow a specific course from departure to arrival. They are especially important in instrument flight rules (IFR) operations where precise navigation is essential.

Considering the other options, while refueling points and altitude indications are relevant in specific contexts, they do not serve as the primary function of a waypoint. Similarly, marking turbulence areas is not a characteristic of waypoints; rather, turbulence information is usually derived from weather reports and forecasts, not indicated by the waypoints themselves. Thus, option C accurately reflects the primary function of waypoints in aviation.