What limitation primarily affects the VOR system performance?

The VOR (VHF Omni-directional Range) system's performance is primarily affected by line of sight. VOR stations transmit radio signals that can only be received by aircraft within a certain range, determined by the curvature of the Earth and the altitude of the receiving aircraft. This means that the farther you are from the VOR station, the higher you need to be to receive the signal without obstruction.

Obstructions such as terrain and buildings can interfere with the reception of the VOR signals, leading to inaccuracies in navigation. Since VOR relies on a direct line of sight to function effectively, any barriers between the aircraft and the VOR station can cause significant issues with signal reception. Therefore, understanding the line of sight limitation is crucial for pilots during navigation using the VOR system.