This paper analyzes and compares previous protection level (PL) formulations used in the evaluation of Distance Measuring Equipment (DME) as a potential Required Navigation Performance (RNP) system to be used in the scenario that GPS and other Global Navigation Satellite Systems (GNSS) are unavailable. Since these formulations were developed for augmented GNSS, we investigate the validity of certain assumptions made for GNSS as applied to DME by deconstructing the formulations according to a general PL framework. DME, for example, contains station monitoring that automatically shuts down stations transmitting out-of-tolerance signals which is not the case for standalone GPS. As the surveyed DME PLs can be categorized as either fault-free or single-fault PLs, we evaluate the performance of representative PLs for these categories and compare the results to the original PL performances. We describe the differences in terms of the assumptions made explicit by the initial deconstruction within the PL framework. As the surveyed PLs are intended for non-DME measurements as well, we offer some brief comments on how such an approach would fit into the PL framework described.