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CRJ skips WPT's on the approach


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Today I had a problem in a short training flight: KSAN/27 RNAV (RNP) Z RWY27 KSAN/27. I departed from RWY 27, heading same course, climbed to 6000, keeping 180-185 kts. I turned to the KLOMN, switched to AP and NAV and DIRECT TO KLOMN, entering the approach. On 6000 and 180 kts, aircraft enetred into approach scheme "RNAV Z RWY27". But after KLOMN instead of heading to AJADE and following CATDG, CRSNR and SAYAE, it just turned to CIJHI.  

It totally ruined the approach, such as I've got to the final on the wrong height, with the wrong speed. I attached the screenshot from this moment and it is also interesting that it did not draw the path trough these way points.

On other approaches I saw same behaviour, several times. I did this short flight on CRJ 700 ver 1.0.0.1.

Could you advise something? Should It be reported as a bug?

CRJ-FAIL_APPROACH.png

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I believe you’re trying to fly an RNP app with RF Legs which isn’t possible in the real airplane or in the simulated one. 
 

You can fly RNAV approaches (no RF legs) down to LNAV mins buts that’s it AFAIK. 

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I discussed this in another post regarding approach problems at a different airport, but it is worth reviewing here.

 

The problem is that this is an RNP/AR approach, and the real CRJ is not capable of flying a AR approach. The “AR” stands for “Authorization Required”, and that means that the aircraft FMS and autopilot have to meet extremely stringent requirements for both lateral and vertical path accuracy - and the FMS has to be able to interpret specific codes found in the navigation database that are unique to AR approaches. These unique codes deal with the specific path the aircraft must follow, and how waypoints are sequenced. “AR” also means that the pilots have to have special training for these type of approaches.

 

The Proline 4 autopilot and FMS do not meet AR requirements - it is, after all, basically a 1989 design in terms of its technology.

 

The real CRJ will not display any RNP/AR approach in the approach selection page. I just verified this in the real aircraft by setting up a flight plan to KSAN. The only runway 27 approaches that are shown are the LOC 27 and the RNAV(GPS) Y, which is a standard “old school” RNAV approach that the CRJ can do with no problem.

 

The databases provided by NavDataPro and Navigraph for the sim version of the CRJ contain every approach for all airports, so RNP/AR approaches will display as selectable options, but there is no guarantee that the sim will fly them correctly. The FMS in the sim was designed using actual Rockwell Collins documentation for the real FMS4200, and since that FMS has no capability to correctly interpret the unique coding found specifically in RNP/AR approaches, neither does the sim version. 
 

The sim CRJ may “try” to fly an RNP/AR approach, but there is no guarantee that it will do so correctly. It  may not follow the correct path, the waypoints may not sequence correctly, and in the case of an approach where the aircraft is required to follow a constant radius, constant descent rate path (like the RNP Y 31L approach at KPSP), the waypoint names on the MFD will not display correctly.

 

One solution would be to filter out RNP/AR approaches from the nav database so they do not appear on the FMS DEP/ARR menu just as in the real CRJ, but the problem with that is that there is a subcategory of RNP approaches in the real world that are not AR, and those the real CRJ can fly.
 

From what I can see in both the NavDataPro and Navigraph databases, the approach title does not distinguish RNP/AR from “plain” RNP, so filtering might not be easy to implement.

 

As a sim CRJ pilot, your best option is to look closely at the r/w approach chart for any RNP approach, and if you see “AR” in the title, (for US approach plates), or “Authorization Required” in the text description section (for Canadian or European plates) either avoid trying to load that approach, or do so “at your own risk” with the understanding that the aircraft may not fly it correctly.

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Yes, you right. I've take a look into navigraph .txt for X-Plane. Way points CTADG, CRSNR and SAYAE are marked as RF in the RNAV (RNP) Z RWY27.

Thank you for clarification! I think it's better to filter out such approaches, like a real aircraft do and at least to add the point about this into FAQ.

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33 minutes ago, GENADOSSS said:

Yes, you right. I've take a look into navigraph .txt for X-Plane. Way points CTADG, CRSNR and SAYAE are marked as RF in the RNAV (RNP) Z RWY27.

Thank you for clarification! I think it's better to filter out such approaches, like a real aircraft do and at least to add the point about this into FAQ.

The CRJ can do a basic type of RF leg - DME arcs are in that category - but it can’t do the type found in an RNP/AR approach. Adding something to the FAQ might be the best option, as I’m not sure if filtering the database is possible. 

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3 hours ago, JRBarrett said:

The CRJ can do a basic type of RF leg - DME arcs are in that category - but it can’t do the type found in an RNP/AR approach. Adding something to the FAQ might be the best option, as I’m not sure if filtering the database is possible. 

So the real CRJ could fly VOR APP using LNAV as well? 

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1 hour ago, fakeflyer737 said:

So the real CRJ could fly VOR APP using LNAV as well? 

I think a VOR approach would be flown in green needles, using the VOR signal directly in NAV mode, unless the approach has a GPS overlay. About the same as flying a LOC only approach. 

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