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VNAV snowflake showing descent command during level STAR segment


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Hi,

 

Flying into KCMO on OMN.CWRLD4.RNAV36L, during the CWRLD4 STAR there's a level segment after crossing LAMMA at 12000. Even though the CDU displays the FMS wants a level segment, indicating that the system understands there's a period  of level flight needed before initiating a new descent later, the VNAV snowflake is showing above profile;

 

image.thumb.png.fcdee72088e3ca2925740ec5fb543f0a.png

 

Is this related to the strange heading from RAMEZ bug that's been fixed for the next release, or something else? Crossing altitudes don't seem unreasonable in the CDU like the heading.

Thanks,

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As far as I know the advisory LNAV doesn’t look at the flightplan. It sees the next constraint is EXBAN with 4000A and that’s what it’s showing. The snowflake will always indicate the VS you would need at current speed to reach the altitude displayed on your MFD at that waypoint. 

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Ok, so we are saying that even though the VNAV profile for all these legs is met as I’m at 12000’ and the altitudes in the CDU reflect this, it’s intentional for the snowflake to be indicating that I’m above the desired VNAV profile at this point because of a future restriction that even the descent profile knows isn’t for long enough away that I don’t need to be descending here? That seems….. odd.  But I don’t have any real world CRJ time to speak on it. I will say that further along on the STAR when it actually becomes time to descend the snowflake pops back into the middle of the range and starts over correctly displaying the required profile for the restriction at 4000’.

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3 minutes ago, Peter Clark said:

Ok, so we are saying that even though the VNAV profile for all these legs is met as I’m at 12000’ and the altitudes in the CDU reflect this, it’s intentional for the snowflake to be indicating that I’m above the desired VNAV profile at this point because of a future restriction that even the descent profile knows isn’t for long enough away that I don’t need to be descending here? That seems….. odd.  But I don’t have any real world CRJ time to speak on it. I will say that further along on the STAR when it actually becomes time to descend the snowflake pops back into the middle of the range and starts over correctly displaying the required profile for the restriction at 4000’.

 

The snowflake is not currently programmed correctly. It works in most situations but improvement is still needed in some areas. In your case since there's a level segment, and you're currently at the correct altitude, the snowflake should indeed be centred. I'm not sure if the advisory VNAV really knows how to handle level segments yet. 

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49 minutes ago, Chaxterium said:

 

The snowflake is not currently programmed correctly. It works in most situations but improvement is still needed in some areas. In your case since there's a level segment, and you're currently at the correct altitude, the snowflake should indeed be centred. I'm not sure if the advisory VNAV really knows how to handle level segments yet. 


Hi,

 

Cool, I thought I was losing my mind ;)

as long as it’s on the to-do list I’m sure it’ll get addressed eventually. Not exactly the most pressing issue I’m sure. Back to the good ol days using rule of 3 it is!
 

Thanks,

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The advisory VNAV does need simecmore refinement. It will probably not be in the upcoming update, since that update concentrates on more serious bugs like the glideslope tracking and throttle control, but it is on the list to be looked at.

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