PMDG 737 Series Post LNAV Update Can’t Hold The Magenta Line

[btacon 1,790]

I have been flying the PMDG Boeings for many, many years now. I’m pretty adept at programming and setting the aircraft up to fly and I have hundreds if not thousands of hours to show it. My point here is I’m not new to these aircraft or their systems but ever since the LNAV are update for both the 600 & 700 I find that at least half of my flights will fly along as if everything is nominal when all of a sudden the LNAV will go into a left or right turn and do lazy circles around the magenta course line. Sometimes it’s it rejoins, often it does not. 

Anyone else, or is it just me?

-B

[Moron 64]

PMDG are going to do an overhaul of the LNAV logic for the 737 product line.   Wait - they just did an overhaul of LNAV logic with the release of the 600.  I'm sure you're just imagining the anomaly you're seeing or it's the fault of Navigraph data.   Wait - PMDG don't use Navigraph data since the LNAV overhaul, do they?   Hmmmm.   Probably, PMDG are going overhaul the LNAV logic that they just finished overhauling.  I'm getting a headache trying to keep everything straight.  

[sniper31 638]

Plenty of flights in both the 737-700 and the 600 in the last week and I have not experienced this issue, or any others for that matter. Both aircraft seem to be performing properly for me, on my flights.

[Christopher Low 5,353]

Those "lazy circles" are an intermittent issue with the old LNAV logic.....

Edited August 10, 2022 by Christopher Low

[JBDB-MD80 1,473]

Its an Asobo issue with navdata , RR. sarcasm runnig out now.

Edited August 10, 2022 by jbdbow1970

[JSmith2112 317]

Haven't noticed anything similar apart from earlier today when I picked up my flight stick which disconnected the autopilot when it moved. Maybe post a route to see if it's something specific.

[Maxis 1,864]

Have not noticed any deviations with the LNAV/VNAV on my flights. But im the type that wont close the doors till the entire flight plan is double checked and all waypoints are making sense and accounted for.

[Gnacino 48]

I'm not flying the 737 yet.  I'm waiting for the 800.  I'm familiar with the 37 on P3d.  I've been flying the HD787 mod and I have that same issue.  The way it was explained to me on their discord  was that it was encountering a "dead zone".  Have no idea what that means.  They said that it was an ASOBO issue.

Gnacino

 

[MySound 403]

My 737 flies exactly the way it’s expected. 

[Bartolet7 8]

Yes, I've had this happen as well. But it is a random event and does not occur on every flight. For me, it seems to only happen at cruise. The oscillations can be quite extreme at times, forcing me to disconnect the AP and lightly steer manually to reacquire the course before engaging the AP again.

Edited August 10, 2022 by Bartolet7

[Sunshine13 234]

yesterday after I programmed the FMC with the wave points was flying from CYYZ to KDCA about two thirds into the flight it started going off course.  After the flight I closed the program and I had updates to install for Windows 10.  Would that throw the 737 -600 off course ?

[btacon 1,790]

2 hours ago, Christopher Low said:

Those "lazy circles" are an intermittent issue with the old LNAV logic.....

I know. I’ve been flying with the “old logic” for years but both of these planes have the LNAV V 2.0 code. As someone else posted here in response it’s random, not predictable but it does occur more than seldom for me at least. 

Currently stumped am I!

-B

[jrw4 624]

FMA readout? Airspeed? AP still engaged [CMD displayed]? Is the AP disconnect on input option enabled? Also, have you checked on the PMDG forum?

If it's reproducible, you should certainly submit a support ticket.

 

EDIT By any chance have any of the Assist options become enabled in MSFS? They should all be off.

Edited August 10, 2022 by jrw4
As noted

[Bob Scott 7,720]

Interestingly, this was an issue in the early FSX versions of the PMDG birds...IIRC, it turned out that overreaction to the sim's turbulence effects was the culprit, and it was solved (mitigated) by turning those effects way down.  I wonder if it's the same gremlin reappearing on a different platform...

[btacon 1,790]

1 minute ago, jrw4 said:

FMA readout? Airspeed? AP still engaged [CMD displayed]? Is the AP disconnect on input option enabled? Also, have you checked on the PMDG forum?

If it's reproducible, you should certainly submit a support ticket.

Howdy. Thanks for the good crumbs but I’m nominal on all those topics and the AP remains connected when this happens. I was hoping someone would say, “Oh yeah…when that happens check X and change Y, but alas not today!

next time t rears I ts head, I f ever again, I will try to gather as much system info at the time of occurrence and open a support ticket. 

Best,

-B