Question about RNAV approaches

[RPRIEVER 52]

Greetings all,I've been trying to learn about RNAV approaches, and have a few questions. As an example, I'm refering to KSJC RNAV (RNP) Z r/w 30R.http://flightaware.com/resources/airport/SJC/IAP/RNAV+(RNP)+Z+RWY+30R/pdfThe number after the RNP on the chart (for example: 0.70) refers to the accuracy required for the FMC, am I correct? In other words, using this approach, an aircraft qualified as "0.70" could join this approach from the southeast (via JILIG, GILRO, MOZIE), but not from the northwest via POCUL, since that approach requires a more accurate system (0.50). Is this right?Also, on the RNAV (GPS) Y r/w 30R chart, what exactly does that "WAAS" info mean? (top left corner of the chart). How does this affect the approach?http://flightaware.com/resources/airport/KSJC/IAP/RNAV+(GPS)+Y+RWY+30RMany thanks.

[503(V) Driver 0]

Hey Ron,The term RNP is "Required Navigational Performance". It's the required accuracy of the aircraft's systems. For example, 0.5 (5/10ths of a mile) is more accurate than 0.7. This determines the MDA on these approaches, as well as routing. I'd venture a guess and say the SFO trans on that approach needs a lower RNP because of proximity to terrain. These RNP numbers are cross checked against the ANP (Actual Navigational Performance) within the aircraft. This updates in real time, and if the ANP is higher than the RNP, the approach is to be discontinued.http://en.wikipedia....ion_performanceWAAS is "Wide Area Augmentation System" and is a more accurate GPS system that utilizes a ground based reporting beacon that cross checks the accuracy of the GPS signal. This enables more accurate height readings for GPS, thereby enabling a pseudo glidepath. That number , I believe, is a channel required by the receiver in the aircraft to continue with the approach.http://en.wikipedia.org/wiki/WAASHope this helps!

[badderjet 181]

I wonder if we'll ever get this message or this ANP in the NGX... :((well, j/k, admittedly this was not quite taken in-flight...)

[scandinavian13 5,192]

ANP of 8.45? What did you do to that poor thing?

[Guy014 9]

ANP of 8.45? What did you do to that poor thing?

Toppled the attitude indicator. Shouldn't be doing spins.

[michal 44]

It is important to realize that aircraft capable of RNAV(GPS) and RNAV(RNP) are two different sets of aircraft.

[badderjet 181]

ANP of 8.45? What did you do to that poor thing?

Yeah I really beat it hard... :(