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FrederikS

RNP/ANP alerts

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Hi everyone, today I tested the RNP/ANP capabilities of the NGX. I made an RNAV approach to LOWI. During the approach I commanded both GPS recievers to fail. After a while the ANP value exceeded the RNP value as anticipated. But I did not get the failure messages as described in FCOM2 (11.31.11). In the manual it says that after 10 sec (RNP was 0,3) I should get a CDU message "UNABLE REQD NAV PERF - RNP" and additionally it should appear on the ND. Neither of that happend. What did I miss? Another thing that supprised me was that when the autopilot captured FAC and G/P (I did not tune in the ILS) modes the ANP value suddenly jumped back to 0,03. Any explanation for that? Thanks in advanceFreddy

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Which approach did you load into the FMC? I flew into LOWI earlier today, but I couldn't find the RNAV RWY 26 approach - only the localizer approach was listed.

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I tried lowering the RNP then failing the GPSs enroute. That did give me the "UNABLE REQD NAV PERF - RNP" message. (This messes up the terrain display, by the way - not sure if that is intentional or not). Since you built the procedure yourself in the FMC I think it might consider those enroute waypoints. You should still get the error, but only after 30s. Did you wait that long?

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@trisager: What are your RNAV settings? Did you enable the RNP/ANP values on the ND and scales on the PFD? I don't think that the self programmed route should matter since the RNP value was 0,3...so when exceeding this value imo I should get the specific warning... Freddy

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@trisager: What are your RNAV settings? Did you enable the RNP/ANP values on the ND and scales on the PFD? I don't think that the self programmed route should matter since the RNP value was 0,3...so when exceeding this value imo I should get the specific warning...
All I did was enter a lower RNP value in the CDU (the default enroute RNP is 2.0 NM), then fail the GPSs. I agree you should see the warning, but I think you have to wait 30s instead of 10s to see it since you constructed the approach waypoint by waypoint. I'm by no means an expert, though. / Tom

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I programmed it in myself. You can find the RNAV approach points on the internet.
If you programmed it yourself FMS doesn't recognize it as an approach. Real approaches can only be loaded as a whole procedure.

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If you programmed it yourself FMS doesn't recognize it as an approach. Real approaches can only be loaded as a whole procedure.
The FCOM suggests the message is independent from approach conditions. Whenever ANP>RNP you should get the message. But I just tried it and confirm, nothing happens.
Since you built the procedure yourself in the FMC I think it might consider those enroute waypoints. You should still get the error, but only after 30s. Did you wait that long?
BTW Where does it say this number? sig.gif

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Which approach did you load into the FMC? I flew into LOWI earlier today, but I couldn't find the RNAV RWY 26 approach - only the localizer approach was listed.
Here you go:http://charts.vacc-austria.org/LOWI/LOWI_Approach_RNAV%2026-RNP_01072011.pdf By the way.....how exactly do you fly this route? It appears you have to cross RTT at/above 9500, and then do a 3.5 degress descent. How do you program this into the FMC? Also, what's that loop on the other side of the chart (WI006/07/08)? I'm a little confused here.

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The FCOM suggests the message is independent from approach conditions. Whenever ANP>RNP you should get the message. But I just tried it and confirm, nothing happens. BTW Where does it say this number? sig.gif
I totally agree the values should be indpendent of the phase of flight. Meaning: if ANP > RNP it should trigger the warning of course with the specified delay.Maybe a real world Pilot Or someone from PMDG can help us out here?!?!Freddy

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With the volume of messages on this forum, your best bet would be to create a support ticket on the website.

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Naaah....it's a minor issue. Don't want to bother PMDG with something that is most likely my failure :-)Freddy

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The table in FCOMv2 page 11.31.11
Ah yeah. Gettin tired, duh...
By the way.....how exactly do you fly this route? It appears you have to cross RTT at/above 9500, and then do a 3.5 degress descent. How do you program this into the FMC? Also, what's that loop on the other side of the chart (WI006/07/08)? I'm a little confused here.
Well first of all it should be in the nav database, but currently it ain't. What you can do though is just program in each waypoint and put the correct contraints on it and fly it using LNAV/VNAV. IAN won't work as it's not a stored route. Also make sure to have the RNP set. This is of course only a workaround... But as long as we don't have the RNP procedures and the NGX doesn't support RF legs, well I guess there is no other way, I don't know. sig.gif

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