"Barry" wrote in message
. ..
unless the navigational station is the primary for the approach (which
could be true for ADF, but not DME).

Except, of course, for the famous VOR/DME OR TACAN Z RWY 15 approach at
Martin State:

http://www.naco.faa.gov/d-tpp/0602/05222VDTZ15.PDF
Are you saying that you can't use the GPS in lieu of DME for that
approach?
Why not?

Yes, because the DME is the "principal instrument approach navigation
source" - that approach is a DME arc to the runway.



A subtle but important observation! Have you won any bets with that one?