By harrison woolley 1361545
#529199 I have just done a full reinstall of p3d v4, and my FLAI folder is in a different drive to my sim but it worked fine before i did the reinstall. the add-on.xml folder is in p3d add ons folder where it before but v pilot can no longer it can't find it for some reason.
By Evan Reiter 1314720
#529200 There have been a few people reporting this issue in P3D v4.4. Someone posted the following on the FLAi Support Facebook group. Not sure if this will help you, but give it a try...

Navigate to C:\ProgramData\Lockheed Martin\Prepar3D v4\simobjects.cfg, and add the following:

[Entry.11]
Title=Flai
Path=F:\FLAI2\SimObjects\Airplanes
Required=True

Where the path is wherever you have installed FLAi.