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  1. #1
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    LNAV Unreliability

    Hello all,

    I've finally gotten the entire PM suite up and running, and am experiencing strange behavior with LNAV.

    After takeoff, while joining an airway, LNAV tracks to the first couple of waypoints with no issue. After passing the second waypoint, the aircraft always makes a turn to the left, about 15 degrees left of the "magenta line." Interestingly, on the CDU legs page, it will show that the next waypoint is about 15 degrees left of where it shows on the map (for example, the CDU screen says 281 direct to the active waypoint, but on the ND it's clearly about a 295 track.

    Any help solving this frustrating issue would be most appreciated.

    Thanks!
    Chris Kilroy
    737NG Builder - Henderson, NV USA

  2. #2
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    Re: LNAV Unreliability

    Hi Chris,

    I dont know if this actually will help you or not, but here it goes.

    I had a similar situation a few years ago and the root of my problem was actually an add on scenery BGL file and AF2 double entries in the addon/scenery folders which created an offset of 15 to 20 degrees on my set up.

    to check if the above is your problem line up on a known runway and then check if your shown heading on the PFD matches the runway heading, also use shift/Z to see the heading of Flight Sim and see what it matches
    if you are on lets say Rwy 25 (normal heading 250) but FS and the PDF pints you in a heading of 235 then its a scenery problem somewhere. if not then Another posibility and one which is easier to fix than the above issue is to try and tick/untik the offset facility in the CDU

    Good luck
    Peter

  3. Thanks ChrisKLAS thanked for this post
  4. #3
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    Re: LNAV Unreliability

    Hi Peter,

    Thanks for your reply. I was aware of the BGL mag variation conflicts (those have bitten me one too many times in the past.. haha), so it was the first thing I checked.

    Interestingly, the problem seems to have been solved by switching from Steve Reyling's newer PM aircraft configuration file to the older PMDG version by Bob Scott. I'm not sure why that would have any effect on LNAV, but as long as the problem's solved, I guess that's all that matters.

    Thanks again!
    Chris Kilroy
    737NG Builder - Henderson, NV USA

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