Originally Posted by
Intruder
It's a technicality and CYA statement on the part of Garmin, I suspect.
If an RNAV overlay is published, you can use GNSS equipment EXCLUSIVELY to fly the procedure.
If there is no overlay, the appropriate NavAids (VOR, DME, etc) MUST be tuned and their "raw data" displayed on the appropriate, certified instruments (per EASA, FAA, and all other A's I know of). Once that requirement is satisfied, NOTHING prevents you for actually using the GNSS equipment as your real-time reference while flying the procedure. Just remember that the tuned NavAids are primary and required, and that you cannot continue the procedure using the GNSS equipment if a primary NavAid should fail.
The reality is that the regulators are way behind the technology. This is especially true for NDB approaches. If you are flying an real world NDB approach and you are not using the GPS for primary track guidance, you are IMO doing it wrong. The only benefit of the ADF needle is as a sanity check that you are in fact pointed at the station.
The safest non precision approach is one where you to break out with the aircraft track aligned with the runway centerline after a stabilized and ideally continuous descent. The
only way to consistently accomplish this, is full use of the precision of the GPS.
The last time I personally have flown a for real in IMC NDB approach without some form of GPS to provide approach track guidance was 1994
