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Displayed VNAV calculations on CDU LEGS page show a climb after altitude restriction in STAR


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Hi.

 

Flying the CWRLD4 arrival into Orlando I notice that the CDU displays VNAV profile altitudes that would appear to ignore the TOD required to meet the crossing restriction at LAMMA. Ref below; you'd need to be much lower than FL390 at OMN to meet 12K at LAMMA (a little lower for the southbound arrivals that require 250/12000 at LAMMA), and then shows weird altitudes post-restriction (12K restriction, next waypoint FL380 and then FL390).

 

I haven't had a chance to see if this is the profile it's calling for in-flight; I don't believe it is, if I set my altitude down to 5K to meet the IAF altitude on the ILS the airplane keeps descending past LAMMA even though there's a long run track between LAMMA and the 5K restriction that can be flown at greater than 250 knots.

 

image.thumb.png.136837c065e824e1232d689b5c1afc11.png

 

Thanks,

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What was your full flight plan? It appears that for whatever reason, your aircraft did not sequence to CRZ mode after your departure, and the VNAV system still thinks you are in CLB mode. Did you enter the FP manually, or import it from SimBrief?

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1 hour ago, Peter Clark said:

Hi,

 

Flight plan was KBOS SSOXS BUZRD SEY HTO J174 ORF J121 CHS IGARY Q85 LPERD OMN CWRLD4 KMCO, entered by hand. 

Thanks. I’ll give it a try. Possibly a discontinuity somewhere near the end of the FP might have caused it. The upward-pointing arrow at LAMMA indicates the FMS did not recognize that the aircraft should be in descent mode when beginning the STAR. 

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HI,

 

I did close all discontinuities (OMN) and also closed the vectors waypoint when adding the ILS 36R approach to the end of the STAR while loading the flight plan.

 

Thanks,

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18 minutes ago, Peter Clark said:

HI,

 

I did close all discontinuities (OMN) and also closed the vectors waypoint when adding the ILS 36R approach to the end of the STAR while loading the flight plan.

 

Thanks,

This is what I show, building the FP manually, setting FL390 as a cruise altitude initially.
 

A couple of possibilities... FL390 would not be correct for a flight that is generally southwest bound. That should be flown at an even FL - either 38000 or 36000.

 

Was FL390 your initial FL, or did you do a step climb at any point? If so, you would need to enter a the new cruise FL on the Perf Init page and EXEC before initiating climb. Making any modifications to perf init, or legs page constraints would also require pressing EXEC. There should normally be a prompt on the CDU after any action that requires EXEC. If that was overlooked, it could have caused the issue. For some reason, your FMS did not know that the aircraft was in cruise mode.
 

 

E080CFE0-34F3-450D-9FEC-2416BF96E2FB.jpeg

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I've noticed a few times where for whatever reason the cruise altitude shown in the cruise waypoints (by which I mean the waypoints where I should already be at my cruising level as opposed to climb or descent waypoints) does not match the cruise altitude that I inputted into the PERF page. For example I inputted FL380 in the PERF page but in the LEGS page my cruise waypoints show FL370. In this case the VNAV won't cycle to CRZ. In order to change this I just change the FL370 shown at each cruise waypoint to FL380 and then it seems to sort itself out. 

 

Could have be what's happening with you @Peter Clark?

 

And just for clarity's sake, and to bounce off of what @JRBarrett is saying, this happened when I was still in the ground doing my pre-flight so it wasn't a step-climb scenario. It's possible that it was an East-West cruising level thing but I honestly don't remember. Either way making the cruise altitudes match the altitude in the PERF page cleared everything up.

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Interesting. I was using FL400 for the flight down. Not sure where 390 came from. I’ll give it a fresh try again tomorrow and see if something different happens.

 

Thanks all,

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12 minutes ago, Peter Clark said:

Interesting. I was using FL400 for the flight down. Not sure where 390 came from. I’ll give it a fresh try again tomorrow and see if something different happens.

 

Thanks all,

 

Good chance that's the issue then. Best of luck!

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18 minutes ago, Peter Clark said:

Interesting. I was using FL400 for the flight down. Not sure where 390 came from. I’ll give it a fresh try again tomorrow and see if something different happens.

 

Thanks all,

Try FL380 and see if it makes a difference. I think there may be a bug in the sim for altitudes above FL390 - I will investigate further, but am now being affected by a problem with the MSFS servers being widely reported on the main MSFS forum where the sim is telling me that “packages are out of date”, and that is now preventing me from going on line. 

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I haven't been getting any vnav help on my MFD or Legs page on any of my flights since the last update.. I have to go to the vnav page and go over to the desc calc to get any assistance. Then I have to be manually typing in the waypoints. Not sure if I'm missing something or if I'm doing something wrong, but I'm doing same things I was before the update and following same steps The Dude showed for setup. 

 

 

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On 4/10/2021 at 4:18 PM, Chaxterium said:

I've noticed a few times where for whatever reason the cruise altitude shown in the cruise waypoints (by which I mean the waypoints where I should already be at my cruising level as opposed to climb or descent waypoints) does not match the cruise altitude that I inputted into the PERF page. For example I inputted FL380 in the PERF page but in the LEGS page my cruise waypoints show FL370. In this case the VNAV won't cycle to CRZ. In order to change this I just change the FL370 shown at each cruise waypoint to FL380 and then it seems to sort itself out. 

 

Could have be what's happening with you @Peter Clark?

 

And just for clarity's sake, and to bounce off of what @JRBarrett is saying, this happened when I was still in the ground doing my pre-flight so it wasn't a step-climb scenario. It's possible that it was an East-West cruising level thing but I honestly don't remember. Either way making the cruise altitudes match the altitude in the PERF page cleared everything up.

Did you have an arrival runway loaded into the FMS at the time? I ran into the same problem myself, and loading a runway fixed it.

This doesn't represent the actual airplane, which can fly around all day without an approach in the FMS and the VNAV works fine - but it may be a workaround until a fix can be implemented.

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35 minutes ago, thecloudcities said:

Did you have an arrival runway loaded into the FMS at the time? I ran into the same problem myself, and loading a runway fixed it.
 

 

Yep I did. I almost always have an approach loaded with a STAR.

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On 4/10/2021 at 5:09 PM, JRBarrett said:

Try FL380 and see if it makes a difference. I think there may be a bug in the sim for altitudes above FL390 - I will investigate further, but am now being affected by a problem with the MSFS servers being widely reported on the main MSFS forum where the sim is telling me that “packages are out of date”, and that is now preventing me from going on line. 

 

Hi,

FL380 does seem to make the CDU happier. It sequences to 12000 for a few legs and then starts the second descent as expected, so you're likely on to something there;

 

image.thumb.png.3294a8ce11b69421ca0b8b681f39dfe9.png

 

One thing I did notice is a really bizarre distance value between RAMEZ and MICKX. It's only 8.8NM

 

image.thumb.png.1e55a89546672de95097f0ee2e5d9d62.png

 

I'm using Navigraph navdata and all the data was prepopulated from the CWRLD4 arrival OMN transition. Not sure if it's navadata related or something in the CRJ. The ND displays the correct route in plan mode;

 

 

image.thumb.png.8b1b03860c6d0c3285aba1389e823af1.png

 

Thanks,

 

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