Why do so many RNAV approaches say RNP-0.3 (DME/DME NA)?
A. DME signal reception is limited to line-of-sight, and for approach operations, the aircraft typically cannot receive very many DME signals. As a consequence, DME/DME performance can be poor, and is frequently inadequate. The FAA is currently working with industry to develop criteria to implement some DME-based capability for approach procedures using the RNP concept.
