At what point is a controller required to advise a pilot of the purpose of a radar vector?

A controller is required to advise a pilot of the purpose of a radar vector when the vector is initiated. This is a fundamental aspect of ensuring clear communication between air traffic control and pilots. Providing the purpose of the vector at the time it is issued helps the pilot understand the reason for any changes in flight path, which can be critical for safety and situational awareness.

For example, the vector may be issued for traffic separation, to assist with weather avoidance, or to prepare for an approach to landing. By clarifying the intent of the vector at the point of initiation, the controller enables the pilot to make informed decisions regarding their flight operations. This communication helps facilitate a mutual understanding of the current context, thereby enhancing overall safety and efficiency in air traffic management.