Which condition does NOT warrant the requirement for DME equipment?

The choice indicating that performing non-precision approaches does not warrant the requirement for Distance Measuring Equipment (DME) is accurate because non-precision approaches can be conducted using other navigational aids without necessarily requiring DME. Non-precision approaches typically rely on equipment such as VOR and NDB, which provide lateral guidance to the runway but do not require the precise distance capabilities of DME.

In practice, while DME enhances situational awareness and can improve the accuracy of positioning during an approach, it is not a mandated tool for executing non-precision approaches. Instead, these approaches can be carried out safely with basic navigational aids.

In contrast, the other conditions listed—operating with insufficient visibility, using VOR navigational aids, and flying over mountainous terrain—often necessitate the use of DME as they enhance an aircraft's navigational proficiency, especially when visibility is reduced, or terrain poses challenges. DME provides pilots with precise distance information, allowing for safe navigation and approach in environments that could otherwise be hazardous.