"Peter Clark" wrote in message
...

Um, OK, I'm thick. I don't get what substitution rule I'm still
missing? With either approach you're using the VOR head for lateral
guidance and reading the distance from some fix in the GPS database
from the GPS head. Even the example approach used for how to do a DME
ARC in the KLN 94 GPS manual is an VOR/DME approach using an arc.


But you're not using the VOR head for lateral guidance and reading the
distance from some fix in the GPS database from the GPS head with either
approach. The VOR/DME or TACAN Z RWY 15 at MTN would have you using DME
for lateral guidance and determining your position on the final approach
course from crossing VOR radials. If you substituted GPS for DME on that
approach you'd be substituting for DME where it was the principal instrument
approach navigation source.