AOPA Online: Air Traffic Services Brief -- Use of GPS in lieu of DME/ADF
Effective July 16, 1998, pilots may substitute IFR-certified GPS receivers for DME and ADF avionics for all operations except NDB approaches without a GPS overlay. GPS can be used in lieu of DME and ADF on all localizer-type approaches as well as VOR/DME approaches, including when charted NDB or DME transmitters are temporarily out of service. It also clarifies that IFR GPS satisfies the requirement for DME at and above Flight Level 240 specified in FAR 91.205(e). This approval represents a major step toward removing the need to retain DME or ADF in our cockpits for any reason.
Note: Air carrier operators should consult their operations specifications and their principal operations inspector for approval.
Limitations
There are still three instances in which DME or ADF are still required.
- NDB approaches that do not have an associated GPS overlay approach must still be flown using an ADF.
- A non-GPS approach procedure must exist at the alternate airport when one is required to be filed by regulation. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate. GPS substitution for DME/ADF is not permitted in this case.
- DME transmitters associated with a localizer may not be retrievable from your GPS until the manufacturer incorporates them in the database. Pilots are not authorized to manually enter coordinates.
Yes, I've underlined a note about the op-specs. This is the FAA's take, but I'm in Korea for the time being.