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P3D v4 AIFP is "unable to access aircraft folders."

Hi Don,

I was absent a while and now went directly from Vers. to Using Win10 Pro 2004. Using P3Dv4.5 HF3. Installed v5 as well but not used for AI yet.

I have my AI folder on the same drive (D:\) but outside of the sim folders, connecting via addon.xml (see attached files).

Starting up (target version P3Dv4) and then the error: "Unable to access aircraft folders"

Tried install AIFP in a new folder. Tried running as administrator. But still the same error.

Still have as a backup and running fine, so no rush.

Thank you.


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Resource contributor
I'm at a loss to explain your situation. I have implemented your scheme on my system (using your files) and AIFP finds the reference to D:\FS_Content\AI\AI\SimObjects\Airplanes and uses it as an aircraft Top Folder. The only reason it would later discard that folder is if it didn't exist.

I have found among my backups and have done a line-by-line comparison of the related functionality. While there were a few minor coding changes (for efficiency), none should have had such a disastrous effect. I would also note that no one else is reporting a similar issue at the moment. That error message is only issued if absolutely no aircraft top folders are found. So, based on your comments that you have installed PV5 but not yet used it, I wonder if your is attempting to start up with PV5 as the Target Version.


Resource contributor
Ronaldo, any update??

It would be helpful to know if you actually see the traffic from a traffic file in your current system configuration - to confirm that Flightsim actually finds and processes the AI.
Hi Don,

traffic files generated with are showing up and working fine. Also edited some of the bgls and compiling again and works without problems. The traffic shows up. I see no abnormalities e.g. AIFP hanging or similar during compiling.

I just copy the AIFP.ini file into the folder. No success, unfortunately.
I completly removed the write-protection of the entire folder. No effect.

I would also note that no one else is reporting a similar issue at the moment.

Not similar to this thread a bit below?

I wonder if your is attempting to start up with PV5 as the Target Version.

Also thought about it, but the dot is on P3Dv4. Do you think I should add the SimObjects folder into simobjects.cfg?

I will add the AI folder into P3dv5 via xml as well to see if things changed.
Don, which add-ons.xml is looking for?

C:\ProgramData\Lookheed Martin\Prepar3Dv4\add-ons.xml


C:\User\Ronaldo\AppData\Roaming\Lookheed Martin\Prepar3Dv4\add-ons.xml

My attached add-ons.xml is in the ProgramData folder.


Resource contributor
Thanks for the updates

Not similar to this thread a bit below?​
No. The issue reported in that thread was due to an identified and fixed problem. If yours were the same issue, it would no longer being occurring

Do you think I should add the SimObjects folder into simobjects.cfg?
That's where AIFP looks first. But, it appears either AIFP is not seeing your C:\ProgramData\Lockheed ...\P3D.\ simobjects.cfg folder or the folder contains no aircraft. Any thoughts why this should be?

My attached add-ons.xml is in the ProgramData folder.
That's most likely the cause. AIFP looks for Add-on.cfg files in ProgramData and for the Add-on..xml file in the location specified in the .cfg file. In your case, the addon is specified to be D:\FS_Content\AI\AI, so that's where AIFP looks. And, if it's there (as it was in my tests yesterday) it will be found.

To confirm this as the underlying cause, please move/copy your add-on.xml to "D:\FS_Content\AI\AI"

The remaining question is can add-on.xml files legitimately be saved in C:\ProgramData. It's not clear from the SDK that this is the case. But, if valid, AIFP can easily look there as well.
My attached add-ons.xml is in the ProgramData folder.
That's most likely the cause

Arrgh I'm very sorry I mean the add-ons.cfg. :oops: the xml file in FS_Content\AI\AI is fine!

Again for clarity

Don, which add-ons.cfg is looking for?

C:\ProgramData\Lookheed Martin\Prepar3Dv4\add-ons.cfg


C:\User\Ronaldo\AppData\Roaming\Lookheed Martin\Prepar3Dv4\add-ons.cfg

My attached add-ons.cfg is in the ProgramData folder.

But anyway, I ported over the ProgramData add-ons.cfg to Roaming add-ons.cfg

And put an entry for the ..\AI\AI\SimObjects in the simobject.cfg.

No effect!

I'm starting P3dv4 right now (takes a bit of time) and try again.


Resource contributor
AIFP looks for add-ons.cfg first in ProgramData and then, if not found, in Roaming and Local (in that order) AppData folders. Then for each addon so discovered, AIFP looks for an add-on.xml file in each addon package.

I have confirmed - again - if the Add-on.cfg file you sent me is in ProgramData and the add-on.xml file you sent me is in "D:\AI_Content" , AIFP adds "D:\AI_Content\A\AI" to the list of Aircraft top folders - assuming the folder exists.

In my previous post I asked you to "please move/copy your add-on.xml to "D:\FS_Content\AI\AI". Those instructions were incorrect, I wanted your add-ons.xml file in "D:\FS_Content". Please give that a try.
I wanted your add-ons.xml file in "D:\FS_Content". Please give that a try.

Done. No changes.

Other idea: AIFP is on Drive E: Copied AIFP into D:\. No changes.

Attached screenshots shows the entire folder structure, below \Airplanes are the ai models.

Thank you very much for this Don, I'm sorry for the trouble.


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Resource contributor
Let me clear one thing up first. The fact that is seems to work in and not in a later release, doesn't make correct. In fact ignores the package name and apparently simply "stumbes" on the Add-on.xml as a result. But, as you'll see in a moment, I believe that the fault lies with Package name.

It is my understanding that your add-on.cfg file is in ProgramData. and I believe AIFP is finding it without difficulty. Your add-ons.cfg contains the following items:

TITLE=Airplanes AI

which, to my understanding should direct AIFP/Flightsim to look for a package ((i.e., a folder) entitled "Airplanes AI" in the folder "D:\FS_Content\AI\AI" in which a file named add-ons.xml should be found.

Unfortunately, according to the listing you posted above, there is no such folder. The addons.xml of interest is in a folder named Content. consequently AIFP never finds the add-on.xml file in the current configuration.

If this is not how P3D add-ons are supposed to work, someone please tell me what is the correct process. If it is, then changing the "TITLE=Airplanes AI' entry in the Add-ons.cfg file to "TITLE=Content" should correct the situation.

Assuming all this worked in PV4, it would seem that the "add-on rules" are more rigid that the implementation.

Edit: My analysis above is incorrect. Upon re-review of the directory listings you sent me, it is clear that the add-on.xml file "lives" in "D:\FS_Content\AI\AI" - which is where it should be. My comment above re AIFP looking for a folder entitled "Airplanes AI" is a consequence of me misunderstanding my own (albeit quite complex) code. AIFP ignores the addon title as, apparently, does Flightsim.

Consequently, I am still at a loss to explain why AIFP is not finding the path to your AI.
Last edited:


Resource contributor
We have both made several mis-statements. So, I think we need to back up a bit. Please confirm:
  • the add-ons.cfg file is in the "C:\ProgramData\Lockheed Martin\Prepar3D v4" folder and no where else,
  • the path to the add-on.xml file of concern is "D:\FS_Content\AI\AI\add-on.xml",
  • one or more valid aircraft exist in "D:\FS_Content\AI\AI\Content\SimObjects\Airplanes, and
  • the line in your aifp.ini file starting with "Target FSVer=" ends with ""P3Dv4"
Assuming all that to be the case, I have attached a version of that will identify the source of the error message "Unable to access aircraft folders". That message is issued in four separate places in the code. I need to know which one. The attached version adds a number at the end of the message. Please run the attached and tell me what number that is in your case.


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Resource contributor
Ronaldo, if there is something in AIFP causing your difficulty, I am very anxious to determine what that something is. Conversely. if you have determined the cause lies elsewhere, then I would like to know that too.

I have once again analyzed the changes in this area of AIFP between and Those changes were made for unrelated reasons and are if no consequence in this issue. The changes determine the title of the addon, which initially led me to suspect the add-on detection code made use of the name. It does not!

So, there is something else at play here. I need you to run the special release I sent you yesterday.
Hi all, I am getting the same error message using FSX on Windows 10, with no add-ons. AIFP installed inside FSX main folder. I'm confused by the xml files and xml files referenced above - I don't seem to have those!


Resource contributor
Inbarnamatt, you haven't given me much to go on since you've told me nothing about the nature/location of your aircraft folders or the release number of the version of AIFP in use. Nor have you indicated whether or not this is a new problem.

The install location of AIFP should be of no relevance, though inside the FSX folder is unlikely to be reflective of most users. Just to be sure it's not a path-confusion issue, I would ask you to re-install AIFP outside FSX.

Also, a couple posts above I attached a special test version of the latest AIFP release. May I suggest you install this version. and report the exact error message. Also, please post your simobjects.cfg file and it's full path.


Resource contributor
Inbarnamatt, yesterday I asked you to post your simobjects.cfg. Since this is FSX, I should have asked for your FSX.cfg file (simobjects.cfg is a P3D "invention").


Resource contributor
Ronaldo, Inbarnamatt, since neither of you have responded to my latest posts, I assume you've found the cause of your respective difficulties and are now able to continue unimpeded. While that closes the matter for me, you may be able to help others avoid similar situations is you posted what was wrong in your systems.
Don, I'm very very sorry but too busy (because of covid19 chaos here) to look deeply into this. And I have to admit that your last post was confusing to me (now edited by yourself in the meantime). I checked this at that time and my setup is compliant with the P3D SDK (see here) with the xml-file in the right place.

But I will look into this again.

Sorry again,


Resource contributor
Yes, COVID has turned most of the world upside down.

Don't know what you found confusing. Basically all I asked you to do was run a special test version of AIFP and report the results, in the hopes that would narrow down what's going on inside your system.

Should you find time to run the test version (shouldn't take more than a minute) I'll take another look. But, since no one else is reporting such difficulty, I have little choice but to assume the issue is internal to your system.


Resource contributor
Just to close this thread, Ronaldo has confirmed via another forum (while this forum was unavailable) that he is no longer experiencing this issue with the latest release of AIFP.

It's not clear why the problem occurred in then first place and no specific action was taken in AIFP to resolve it. Ronaldo reports
I have my AI folder on the same drive (D:\) but outside of the sim folders, connecting via addon.xml (see attached files).
It doesn't matter to AIFP where your aircraft are located. AIFP looks in the same places as Flightsim for aircraft folders, ie, first, the locations defined in the simobjects.cfg file in ..\ProgramData and, for P3dv3 and later, in addon.cfg folders. Unless you have reconfigured SImObjectscfg, stock aircraft will be defined there. So, if AIFP reports it is unable to locate any aircraft folders, it is most likely that there is an error in simobjects.cfg or that file is not accessible to AIFP. If it's only certain aircraft folders that are not found, the problem is either in the associated addon.cfg folder or if specified via a new entry in simobjects.cfg, then there.