I am having an issue while in LNAV mode where I deviate from the enroute course to 30 degrees in another direction while flying the 747-8i.

 

I am flying from KSFO-->KJFK and all is fine for the first 1/3 of the flight and then the plane deviates for no reason and the at some point it corrects itself or I disengage the LNAV and I have to engage the AP HDG to get back on course. I turn the LNAV on again to pick up the next waypoint and then it starts to happen again.

 

I would appreicate any direction you give me on this item

I had this issue a little while ago, possibly caused by a scenery addon. Sceneries with incorrect, corrupt or even old FS9 format AFCAD data used in FSX can cause this.

 

The aircraft would track "offset" the centreline of track, and a few degrees off expected heading *around 20 to 30° off*. When rolling down a runway on centreline, it would appear to be skewed at an angle to the runway centreline and travelling diagonally across the Nav display, staying on the non-centred centreline.

 

In my situation I managed to Fix these symptoms by doing the following:

 

Step 1: Download the Flight1 Registry Repair Tool at www.flight1.com/view.asp?page=library

Step 2: Run the Registry Repair AS ADMINISTRATOR

Step 3: Download the Magvar data at http://www.aero.sors.fr/navaids.html

Step 4: Run the file As Administrator.

 

Test your 747 and MD11 in the area you noticed the issues. Perhaps re-run the flight you discovered the problem.

 

Remember, if you don't run As Administrator (Right click, "run as Administrator") the fix won't work. You may need to move the file(s) out of the ZIP to do this.

 

Run as admin may not be needed for Windows XP and earlier. It is deftinatley needed for Windows 7.

 

The PMDG NGX does not appear to suffer from this problem, only the 747x and MD11, likley something to do with the 747 and MD11 using the FSX default magnetic variation stuff, and the NGX not doing so. I suspect 777 will be like NGX in this respect.

Welcome to AVSIM!

 

I believe performing the first two steps described by the previous poster should be sufficient. Most people find success after running the Flight1 Registry Repair Tool alone. In any case, try it before adjusting other FSX data.

Thanks guys. I took your advice and it looks like the deviating stopped.