PPT33R wrote:

I can't see that happening, especially when RNP is being deployed
commercially. Boeing & Airbus are now certifying their newer airframes
for RNP .1, which allegedly integrates GPS, INS, and DME into the FMS.
The GPS portion requires RAIM and is much more reliable with WAAS.

TIS, on the other hand, is a whole other issue...

I am involved in the work being done with RNP. WAAS is not part of the
calculus at all in the FMS sensor hierarcy for RNP_SAAAR instrument
approach procedures. RNP 0.10 is acheived through complex interfaces of
FMS software with GPS as the primary sensor. WAAS is not used. The most
robust platforms (dual-thread aircraft, which will be a requirement where
RNP is needed for the missed approach, use blended, updated IRU position
along with GPS (or without GPS for a reasonable period of time in the
event GPS suddently fails).

WAAS's primary benefit is to provide the LPV glide-path for the LPV final
approach segment. The RNP_SAAAR criteria's final approach segment
glide-path is predicated on IFR-certified Baro VNAV.

As an aside, when the FAA commissioned WAAS, they "dumbed down" the Baro
VNAV criteria for public RNAV (GPS) IAPs, which increased existing VNAV
minimums. This was a blatent political move to make LPV minimums look
better.

The assessment concets for the VNAV obstacle clearance surfaces in the
RNP_SAAAR environment rightfully do an end-run around the dumbing down of
public VNAV obstacle clearance criteria.