Thanks Tim and Gene for you insights. I'm told Alaska Airlines has
rnp .1 approval for some approaches up there. I presume this must be
IRS (for smoothing) with gps feed for accuracy.
Stan

On Thu, 23 Dec 2004 04:44:35 -0800, wrote:



wrote:

Most RNAV approaches have the notations:

"GPS or RNP - 0.3 required", and
"DME/DME RNP - 0.3 not authorized"

1. The "or RNP .3" seems to imply some navigation unit other than gps
can have rnp .3 Any idea what?

There is this "fairyland" concept that RNP is sensor independent. This is
true for large numbers, where INS or IRUs will provide the integrity and
accuracy required. But, with small values such as RNO 0.3, it is almost
impossible to satisfy the RNP qualification requirements without GPS as
the primary sensor.



2. If an FMS with rnp .3 is able to conduct this approach, wouldn't
it need a gps input to be that accurate? Surely IRS with dme updating
can't be used for any non prec approach?

The airline industry conned the FAA to let them use IRUs and DME/DME for a
couple of years, until some dramatic map shifts almost caused a couple of
CFIT accidents.



2. Any approaches where dme/dme rnp .3 IS authorized?


Only with specials at a few locations with very robust DME reception down
in the weeds. There are no public procedures.