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Posted (edited)

Hello

Xplane 10.51; Win 10 64. Ixeg 1.0.7

When in a desc- cruise also- I will disengage  vnav in favor of V/S decent. The LNAV light remains on, CMD A is still engaged, but the A/C continues on whatever heading it was on when I disengaged VNAV. I have to either select HDG mode or go to the CDU and activate the current fix where the magenta line updates and the A/C then follows the route.  

Any idea?

 

Thank you

Steve

Edit: Looks like lots of vnav issues.  Suppose it could be related.

Edited by ortegas
Posted

It´s perfectly normal for the plane to fly the current heading when you disengage/change a VERTICAL mode. The direction of the plane is determined by the LATERAL mode (LNAV, HDG, CWS R), while the vertical patch (pitch) is controlled by the VERTICAL modes (VNAV, V/S, FLCGH, CWS P).

So I think you are not seeing VNAV issues but rather a problem with understanding autopilot modes.

Cheers, Jan

 

Posted

Thank you for the reply.

 

So, even though LNAV and VNAV are both engaged, and the aircraft is following the magenta profile, once I disengage VNAV then LNAV disengages too?  Then why doesn't the light extinguish (just as the VNAV light extinguishes) showing this behavior?  It remains on leading one to believe that the lateral profile will still be followed even though the vertical profile has been changed.  Always learning. :-)

 

Thank you sir.

Steve

Posted
32 minutes ago, ortegas said:

Thank you for the reply.

 

So, even though LNAV and VNAV are both engaged, and the aircraft is following the magenta profile, once I disengage VNAV then LNAV disengages too?  Then why doesn't the light extinguish (just as the VNAV light extinguishes) showing this behavior?  It remains on leading one to believe that the lateral profile will still be followed even though the vertical profile has been changed.  Always learning. :-)

 

Thank you sir.

Steve

 

Steve

 

If you are flying VNAV / LNAV engaged and you change vertical mode by pressing V/S or FLCH for descending, LNAV should remain engaged and the the aircraft should remain following the magenta.

If the aircraft stopped following the magenta while you engaged another vertical mode, something else happened unnoticed. If you see this behaviour again please capture and attach here a few screen captures of your forward cockpit to see what FMA a/p modes are telling, what the displays are telling, what the fmc is showing for diagnosing.

  • Upvote 1
Posted

I do also forgot to mention, the aircraft may stop following the magenta under certain rare conditions (known bug being worked on for the next update), maybe we have had a bad coincidence here. Maybe the aircraft just stopped following the magenta earlier unnoticed and you assumed it happened while you disengaged VNAV.

Posted

It has happened to me twice.  I will try to emulate the flight again and if it occurs I will post a screen shot.  It might be a few days since my work week has commenced.  Thank you very much.

 

Steve

Posted
24 minutes ago, ortegas said:

It has happened to me twice.  I will try to emulate the flight again and if it occurs I will post a screen shot.  It might be a few days since my work week has commenced.  Thank you very much.

 

Steve

do you remind the details of your flight?

origin/destination airport

departure runway and arrival

departure prcedure, transition, route, transition, arrival procedure and approach?

entered data, flight level, etc?

 

i can try to replicate your flight over the weekend and see if i do get same result.

Posted

Hello

The flight was from KLAX to KSFO.  

VTU7  RZS SERFR SERFR2 (or WWAVS1 can't remember which)

FL 360 or 380

Departed Rwy 25R Landing ILS 19L

Startup from cold and dark

I dont remember A/C specifics. I believe ZFW was over 90,000 lbs and fuel for 500 mile leg.

It happens on descent. I really can't remember if it was on the star( I think this) or if I was vectoring for the app.

Changes, I believe, we're made to the CDU to mimick the star restrictions.

Thank you

Steve

Posted

A good habit to get into is to always keep the heading bug lined up with the direction you are to follow..just incase the LNAV for some reason lets go you can quickly choose HDG and maintain the same direction until you find the trouble that caused it to let go..or mabe a bug raising its ugly head.LOL

  • Upvote 1
Posted

Hello,

Sorry it has been a bit.  I wish I had more time to put into this fine hobby.

Anyway, I took another flight,  same city pair, and the anomaly did not reproduce itself.  I even tried different climb/descent modes.  The LNAV acted as I anticipated.  I will try it again a few more times-as I plan on flying the airplane quite often.  If it happens again I will take a snap shot of the issue and post.  I am pretty sure I was seeing something not quite right, twice in fact.  But alas I am no pilot so my procedure could have been faulty. 

Thank you for all the inputs.

 

Steve

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