Can an approach-certified GPS be used to substitute for NDB and DME
during an approach (or even en route)? What if the approach says ADF
Required or DME Required? My understanding of the AIM is that you can
only use the GPS as a substitute when there is a published GPS overlay
for the approach.

My understanding is that it can, except for an NDB approach. If the NDB
approach has a GPS overlay, then it is a GPS approach anyway.

Jose
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