What is the consequence of selecting a VOR NAVAID that does not have DME service while navigating using VOR/DME based RNAV?

Choosing a VOR NAVAID without DME service while navigating with VOR/DME based RNAV leads to a loss of RNAV capability. RNAV systems often rely on distance measuring equipment (DME) to provide accurate positional data in conjunction with VOR signals. Without DME, the system cannot determine the aircraft's distance from the VOR, which is essential for maintaining the desired track and properly executing course guidance. This absence of distance information can hinder the navigation system's effectiveness, thereby compromising the ability to navigate accurately.

The other options imply favorable outcomes, such as improved accuracy or increased efficiency, which are not realistic when DME is unavailable. Additionally, while manual calculations might be necessary, the primary issue is that RNAV capabilities are heavily dependent on the integration of both VOR and DME data.