Allright I’ll put some context 
simulator is MSFS 2020.
The FMGC exemtion error specifically surfaced in the P3D era where the accumulation of airacs over time made the product give this error.
This since has been resolved on FSlabs side, with the update of their control center software who would manage this.
Old topic of this error back in the day as example:
MSFS specific:
When updating the airac via navigraph hub, it puts it in a specific folder %appdata%\FSLabs_NavData
Then Fslabs makes some sort of copy as they need the .rom file in a different folder (don’t ask me why) which is fsl-common\FSLabs\NavData (located in the same subset of folders)
This is just the general side of things.
To a few customers of Fslabs it happens that when updating the airac, it somehow generates a fault within the product and there are a few theories as of what this error (which makes the product unusable) causes.
A quote from the fslabs forum (fslabs teammember) : “For a small subset of our customers, our navdata supplied by Navigraph is getting corrupted during download. This could be anything from localised ISP issues, to a transient issue with Navigraph’s infrastructure that services said download. Both situations are entirely out of our control.”
possible solutions given, are the following:
-
Manually dowload and copy the airac .rom file
-
Browse to %appdata%\FSLabs_NavData and delete the entire NavData sub-folder
Browse to fsl-common\FSLabs\NavData and delete the problematic .rom file
Return to Navigraph Hub, and FSLabs Navdata should now say “Install”. Proceed with the install, and then launch FSL Control Center. This latter action automatically copies the rom from %appdata%\FSLabs_NavData\Navdata to fsl-common -
Uninstall airac, uninstall product, install product, install airac
For solution 1 and 2, it seems the fix is hit or miss, sometimes it works but surely not all the time.
Solution 3 is guaranteed to work. however time consuming and not efficient.
The problem described is a tricky one, as there are not much reports of this error, one solution will work on one system but not on the other etc.
As the problem in essence is that the product can’t read the airac i’m very much trying not to point fingers in who is the right person to talk to if that makes sense
I’m doing my best to make it a bit clear as to what the issues persists of, if you need more please let me know.
thank you!
