GPS accuracy/deviation scaling

[Cecco]

As far as GPS accuracy is concerned, it says in the FMS manual (Collins 3000) of my a/c that the following criteria must be met: 4 NM oceanic/remote, 2 NM en route, 1 NM terminal and 0.3 NM final approach. Then, in another booklet by Rockwell Collins, the enroute accuray to be met is 5 miles. I found the same information in the CAA Cap 773. There is nothing specific mentioned like P-RNAV or a certain RNP value required in the three sources I mentioned. Any inputs?

[Romeo Bravo Zulu]

GPS is now accurate to 6 metres or one metre with differential GPS
after Bill Clinton disabled SA selective availablity which put the old accuracy around 200 metres does that help?

Have the publications been updated to allow for SA?

Cheers
RBZ

[kijangnim]

Greetings,
There is a difference between GPS accuracy and Required Navigation Performance,....
View the RNP as a tube, and the Accuracy as a ball, the ball has to be smaller than the tube...:ok:

[Cecco]

You're right, kijangnim, I mixed up the definitions: RNAV (RNP 5) must meet a track keeping accuracy equal to or better than +/- 5 NM (PRNAV=1 NM) for 95 percent of the flight time. It has nothing to do with GPS accuracy. So I gather the 4/2/1/.03 values are the full-scale deviations on the cdi, which become more and more sensitive as the a/c enters the terminal area and then to the approach.

What is still confusing to me is that the enroute RNP requirement is stated once as 5 NM and then 2 NM (I didn't find contradicting values for the other phases of flight except the enroute segment).

[FE Hoppy]

On another type the default value for en-route is RNP-2 but this will change to the remote value of RNP 10 when you're a certain distance from the closest land based nav aid in the current Nav data base. As RNP is implemented with different values in differant places some may require RNP 4 and others RNP 10.

I think south china sea/ pacific is RNP 10 and west atlantic may be RNP 4 so the manufacturers are having to change/ update their own equipment as these regulations come into force. Yet another example of ICAO not really doing what they are mandated to do.

[iptamenos]

Remote Oceanic: RNP in a specific area NAT 12.6, WATRS West Atlantic Route Structure 4 and 10 since last May 2008, EU SAM 10, Pacific 10, AORRA Atlanic Ocean Random Route Area 10, IORRA Indian Ocean 10, SCS 10.
Enroute: USA 4 and Q routes 2,
EU BRNAV requires accuracy of 5nm on the track is not RNP you can fly without a data base.
Terminal: USA RNAV1 RNP1, EU PRNAV RNP1
APP: RNAV RNP 0,3,
RNP SAAAR Special Aircraft and Aircrew Authorization Required which in EU is called RNP AR Authorization Required 0.3, 0.20, 0.15, 0,10
FMS Data Base has the required RNP and deflects the CDI to the second dot when the ac position away of the track is equal to the RNP value. The switch from one RNP value to the next happens automatically at certain distance before entering a RNP area.
GPS accuracy 100 m 95%, 300m 100% of the time. Proposed new high accuracy RNAV approaches will be like CATII, 3 down to 0 lateral and Vertical error, and will require WAAS or EGNOS high accuracy GPS signals.
RNP applies to an area, also in different context RNP to a type of RNAV operation requiring additional performance capabilities (AC equipment nav containment, perf monitoring and alerting capabilities.
Iptamenos

[c100driver]

Yet another example of ICAO not really doing what they are mandated to do


Not really a fair call on ICAO as these procedures have been developing independantly in different states faster than ICAO can herd the cats (individual states). They have been doing some great work trying to get agreement from all states and the "Performance Based Navigation Manual" is a good easy to use document, that is attempting to get us all singing from the same song sheet.

The third edition 2008 PBN maual is available on the net search for DOC9613. The EU have said that the PBN Manual is to replace all EU PBN and RNAV when published.

ICAO has to work on consensus, not dictatorship or even majority which is why it takes so long!:eek: