DME/DME IRU for GPS APP
 

Is it legal to fly an RNAV approach with GPS in the title in an aircraft with only DME/DME as the main navigation source in the USA? (B737-300/400), was there ever an Advisory Circular that gave guidance on this?

Don’t know but a very quick sample of some RNAV approaches from some of our destinations show that they all have the statement ‘GPS required’ and I think the clue is probably that GPS is in the title of the approach.

barrow

I don’t think so. The problem with the accuracy of DME/DME depends on the crossing angle of the aids relative to the aircraft.

There was a paper DME/DME for alternate position published for consideration of using DME when GPS is out of service - but I haven’t seen anything adopted. When it is, I am sure it will be reflected in the title of the approved approach.

I would be surprised if the ANP was within the RNP criteria for the approach design for one thing, and also there is the monitoring aspect. As deltahotel says, GPS is required on the plate for all the approaches I’ve looked at...

barrow

“NOTE-

Approved RNAV systems using DME/DME/IRU, without GPS/WAAS position input, may only be used as a substitute means of navigation when specifically authorized by a Notice to Airmen (NOTAM) or other FAA guidance for a specific procedure. The NOTAM or other FAA guidance authorizing the use of DME/DME/IRU systems will also identify any required DME facilities based on an FAA assessment of the DME navigation infrastructure.”
See 3.2.2 An RNAV system with DME/DME/IRU

All RNAV IAPs in the U.S. include GPS in the title. That excludes DME/DME.

https://cimg8.ibsrv.net/gimg/pprune....fb1b9ac011.png
If you look at the notes, "DME/DME RNP 0.30 Not Authorized" seems to be a moot point, why put it on there? or is the notes referring to the convention of enroute-arrival or missed approach requirements, I see this note on many GPS approaches and am thoroughly confused by it.

If your only means of achieving RNP of .3 is via DME, you can’t do the procedure.

How could your only means of RNP 0.3 be DME/DME? you have an approach certified GPS as installed equipment like the title says "GPS". Then why have the note?

That is no longer convention in the U.S. That note will be replaced with "RNP Apch" as IAPs are updated. That will take many years.

https://cimg9.ibsrv.net/gimg/pprune....79ad662b9e.jpg

Pretty sure the Baro-VNAV requirement covers this...

How would that pertain to horizontal navigation requirements?