What is the difference between primary and secondary navigation aids?

The distinction between primary and secondary navigation aids lies in their essential roles in navigation. Primary navigation aids are those that are critical for ensuring the safe and accurate navigation of an aircraft. These could include systems like GPS, VOR (VHF Omnidirectional Range), and NDB (Non-Directional Beacon), which provide the fundamental data necessary for a pilot to maintain orientation, track their course, and ensure safe landings.

On the other hand, secondary navigation aids are supportive in nature and are designed to enhance the navigation process, although they are not strictly necessary for basic navigation. Examples might include DME (Distance Measuring Equipment) or GNSS (Global Navigation Satellite System) augmentations that provide additional information for improving the accuracy of navigation or situational awareness. Thus, while primary aids are indispensable for conducting flight operations safely, secondary aids serve more as enhancements that contribute to the overall effectiveness and efficiency of navigation. This fundamental hierarchical difference explains the correctness of the selected answer.