PBN Approaches using DME/DME
For those of you flying ancient a/c , e,g. 737 classics/NG , early ATRs, Dash 8 , etc,, : when flying a RNP/PBN approach , if you loose GPS, is it easy or adding significant extra workload to switch to DME/DME nav ( provided there are DMEs around avail of course) , or is it transparent like on the Airbus ( using the MMR) ?