What equipment usually accompanies VOR for enhanced functionality?

The correct answer is based on the enhanced capabilities that Distance Measuring Equipment (DME) brings when paired with a VHF Omnidirectional Range (VOR). VOR is primarily used for navigation, providing pilots with directional information to and from a ground station. However, VOR alone does not provide information about the distance to the station. This is where DME comes into play.

When used in conjunction with VOR, DME allows pilots to receive real-time distance information in nautical miles, which significantly improves situational awareness and navigation accuracy. This combination enables a pilot to both determine their position relative to the VOR station and know how far they are from it, facilitating more effective route planning and descent profile management.

The alternative options do provide additional functionalities in various contexts, but they do not enhance VOR in terms of distance measurement as effectively as DME does. For instance, an NDB (Non-Directional Beacon) supports an entirely different type of navigation using directional radio signals, GPS provides satellite-based navigation independent of VOR, and Mode S transponders are more related to surveillance and communication in air traffic management rather than enhancing VOR's core functions directly. Thus, DME is the most appropriate choice for enhancing the functionality of V