I have had the 737NGs for some years and they have always been 100% reliable (well, 99.99%). But suddenly the LNAV function is showing very odd behaviour. Can anyone please help (FS9)? Previous posts haven't lead me to any conclusions ...The a/c doesn't seem to want to follow the flight path - I've posted some screenshots showing the cockpit instruments and FSNavigator. When the 737 approaches a waypoint, it bends quite sharply away from it, to intercept the solid magenta line, placing it off course according to the GPS and FSNav. It then slowly turns itself back on course, but is always about 5kms off the path shown in FSNav/GPS.Why isn't my fligthpath coinciding with the magenta line? I thought it was weather, but with winds aloft disabled things are no better. Reinstalled the a/c and then FSNav - but still the same.Hope someone can help as I now wend a rather snake-like path to my destination: the 737s always used to follow the flightpath just fine, so I have no idea what has gone wrong. The FMC is, I am sure, programmed correctly before take-off and the 'legs' page shows nothing odd...Thanks,Martinhttp://forums.avsim.net/user_files/187200.jpg

Don't think I made this clear above: when the a/c gets to 3nms from a waypoint it turns sharply away from it (maybe 30-40 degs), then very slowly turns back towards the flightpath (but rarely makes it before the next waypoint). It is really odd - and very annoying, so I hope someone has some suggestions! It's not happening in FS9 default planes, BTW.:-)

Do you know how to user "search" option?Go to the advanced search and find all threads in this forum that have 'LNAV' in the title - you will find extensive info related to your problem.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

Yes, of course I know how to use search option. I spent an hour at least going through dozens of LNAV threads today but found no help that solved the problem, as I said. If I had, I wouldn't have spent 15 minutes composing my question, above.Maybe I missed a relevant thread. If so, it'd be good if you'd point me to it.Otherwise: I was going to say that the same thing happens when the a/c intercepts the localizer: it turns away then gradually bends back, but never in time to make a landing on the specified runway.

You've installed something (probably an AFCAD or other scenery file) that mucks with FS's magnetic variation data. That is the cause of this in 99.9% of the cases.

Hmmm, maybe so. I'll try uninstalling the last few scenery additions I've downloaded and see if that helps. The PMDG a/c were all OK this time last week...Thanks. Will report back if this solves the problem. Otherwise, waht with other problems, I'm heading for my 3rd. complete PC wipe/reinstall this year! Sigh...

This is the first time I've seen a general aviation garmin in a Boeing?!?

I put it in there to get various bits of information that I can't otherwise access without pausing the sim. Most of the time it doesn't show of course..:-)

Ryan. This is definitely related to an addon scenery, as you suggested - I deleted all 3rd. party entries in my scenery.cfg file and the problem is solved. All I have to do now is find the culprit and get rid of it permanently. Martin

Thought I'd post back as to what the problem was, as this is something I have never encountered before.Turns out that I had installed a scenery of Aegean Islands recently - it showed up as active in the FS File Library, but was nowhere to be found when searching the scenery.cfg file. I didn't know that this was possible - I thought the scenery.cfg file was an accurate reflection of what showed in the FS scenery library.Whatever, I deleted the scenery in the file library, added it once more and now it shows up as it should in the scenery.cfg file. And my flights are all back to normal...

There you go... it can be literally any scenery anywhere in the FS world, not necessarily where you're flying.

Yes, indeed. I've had some very odd things in the past - like scenery in Japan causing CTDs in the USA..Thanks again Ryan for the lead, I doubt I'd have thought that addon scenery was at the root of the problem: you saved me from an imminent reinstallation of FS9 from scratch!!Martin

>You've installed something (probably an AFCAD or other>scenery file) that mucks with FS's magnetic variation data. >That is the cause of this in 99.9% of the cases.Ryan, with all do respect I think it's rather disingenuous to hide behind the skirts of another scenery causing the problem. While I agree it maybe, in the way PMDG software interprets the navigation data, the fact is all other aircraft, default, 3rd party aircraft including other complex aircraft like Level-D, does not exhibit this problem. If the problem was solely the scenery it would be global. So when all is said and done this still appears to be a PMDG problem in the way it handles MagDev data. Especially now that it appears the problem is not only with the 744X but spans other product lines as well as platform.

i must agree, the LDS 767 and Flight 1 ATR both work just fine for me, its only the PMDG 737 and 747 for FS9 (i dont have the 747X, so i dont know about that one)ive tried everything short of a re-install of FS9 and the aircraft...i tried removing FSUIPC as someone suggested, i tried the updated magdev.bgl file in the avsim libraries, i tried disabling all add on scenery (the only ones i have are the updated time zones and FS Global, and it worked fine in harmony with both those at one time)i think enough people are having this problem and theres been no word whatsoever from PMDG regarding the issue...wheres this so-called "support" in this "support forum"?

It is true, as I said earlier, that default a/c were not affected by the problem: I didn't try LVL-D 767, quite possibly it would have been OK. When you say "enough people are having this problem" are you talking about exactly the same thing I posted about? In four years of having PMDG a/c installed, this is the first time I have encountered anything like this. The problem affected FSNavigator too, with a/c showing as being 20 degs off course.Martin