FS2004 Help adding simple autopilot to vintage aircraft


Resource contributor

I've recently downloaded this package for an updated Default FS Ford Trimotor from flightsim.com (filename in library: new_4at-e.zip), and it contains a really nice but simple autopilot gauge that I've been trying to add to David Molyneaux's Airspeed AS.5 Courier (filename in flightsim library: airspeed_courier.zip).
This autopilot gauge simply holds the Altitude and/or Heading that the plane has the moment you flip the switches (or click the respective assigned keys in your keyboard). This is in my opinion a much simpler, cleaner looking and ''legit'' way of having an AP in vintage aircraft (as opposed to simply add the Bendix AP to the panel :p ).

I decided to add the gauge to several other vintage aircraft I have, which I have done so successfully simply by adding the relevant gauge.xx..... line to the panel.cfg (making the switches show up in the main panel), and changing the "autopilot_available=" from 0 to 1 in the [autopilot] section of the aircraft.cfg.

All the aircraft I have updated with this AP gauge so far have it working flawlessly; but now enter my problem with David's Courier:

The AP holds the altitude correctly, but if I select the heading hold, the airplane just starts banking more and more to the right, until it enters a downward spin and slams into the ground!!
I compared the Courier's aircraft.cfg [autopilot] section with the same section in my other successfully AP updated aircraft and nothing unusual sticks out... though I'm not very knowledgeable of this particular section of the cfg file.

If someone could help me figure out this problem I'd be very grateful!

I can post the relevant cfg entries, and the xml text of the gauge if it's also relevant!

Thank you

Leonardo Santos


Resource contributor
UPDATE: I'm not sure if this is also relevant, but I just noticed that while all the aircraft where the AP works perfectly make a warning sound when I disengage the Master Switch (even though the sound is not the same in all aircraft), in the Courier there is no sound!

Leonardo Santos


Resource contributor

I've tried everything I can remember, even copied all relevant entries from the cfg file of aircraft where I installed this AP and it worked perfectly, to the Airspeed Courier's cfg file but still the same 'bug' :(
It just won't hold the heading! It just banks endlessly to the right!
I'm at a loss here, left scratching my head over what could be happening?

Hello Leonardo

Try to test all gauges first, one by one and see what happens... I am saying this, because sometimes several gauges may interfere
with each other. Another reason might be: this behavior could be present if some gauge and/or files are missing in the current aircraft you're flying.

Another hint: try to use exactly the same panel folder and gauges that actually are working in the new aircraft and take notes on the behavior. Then, try to copy and rename the working air.cfg from the working aircraft into the second aircraft and third, combine all together from the working aircraft to the problematic one and see -yes, again- what happens. In this way, you can methodically track down the problem.

All the best,


Resource contributor
Hey antaris,

Thanks for your reply.
Well I copied the complete autopilot gauge when I extracted it from the original .cab file, so I'm pretty sure there are no files missing there.
I don't quite understand what you mean by ''test all gauges one by one''.
Also in your second suggestion do you mean that I try to use a panel from another aircraft (that has this AP working) with the problematic one?

Hello Leonardo

I had a "typo" when I wrote this:
To what I was trying to make reference, was the general name convention for the *.air file inside any aircraft folder (where the * could be any name). Sorry... my mistake.

Let's try another way to tackle this. You mentioned two aircrafts, the Ford Trimotor and the Courier.
  1. Before to continue, I will assume that you already have the Ford Trimotor and the Courier original files in a safe place; in other words, you have a backup of everything related for both aircrafts.
  2. Also, I am taking from granted that you know how to properly install aircrafts and the Ford Trimotor works as it should inside the simulator (including the autopilot!).
  3. In order to test my theory of the problem, you need to take the panel folder inside the Courier and rename it; for example, panel.courier.
  4. Then, copy the panel folder inside the Trimotor and paste it inside the Courier folder.
  5. Run your flight simulator, choose the Courier with the "borrowed" panel folder and see if the autopilot stops to behave like you mentioned.
Come back to share the result.


Resource contributor

So I interpreted the second part correctly ;)
I will try to do this and see if anything changes then.



Resource contributor

I just tested with the trimotor panel and the same thing still happens... :/
I can only infer that it's something related to either the aircraft.cfg, the .air file or the model itself (though can't really see how the latter could pose a problem).



Resource contributor
Ok so after some more troubleshooting I figured out that the issue lies with the Airspeed Courier's .air file...

What I did was copy an air file from another aircraft where I've installed this Autopilot and got it working to the courier's folder, assigned a fltsim entry to it and started a flight with it; which I believe was something you first suggested, antaris.

Surprise, surprise! The autopilot now works! But obviously I can't make this a solution,since the flight controls and the aircraft's CG felt very wrong (from it being assigned an air file not designed for this model).

So now I ask if anyone can help me figure out what to do or how to edit the air file to fix this, probably help em identify the problem as well, since I have 0 experience dealing with air files :/


Here is the right tool for you; it will help you to open "*.air" files:

Look for "AirEd152 Update".

Bare in mind, that in a file like this are a lot of things to take care of. Before you try to modify something, read the documentation. Also, several entries you may find inside each and every air file requires advanced knowledge. The bright side is that you are free to test whatever you need.
A fair warning: Take notes on every single change you made and save the "air" file with different names; so it should be easier to go "backwards" if you don't like the results. A sample of a naming convention like this would be:

Courier.air (your original "air" file).
Courier_01.air (the file with your first modification).
Courier_n.air (the file with your "n" modification).

Of course, you will need to make a copy of the Courier_n.air file and rename it as Courier.air in order to test the results. I am sure you got this point, right?

Good luck and have fun!

Roy Holmes

Resource contributor
Before you do anything with the .air file please consider the following.
1. If the airplane flies normally with no autopilot selected and turns hard right with the autopilot selected, the fault must lie with the autopilot.
2. Since you have an autopilot section in your aircraft.cfg, that would override any antique autopilot section that might remain in your air file.
3. The air file cannot of itself affect behaviour with the autopilot selected.
4. The Trimotor has three engines. Are you sure they are all operating similarly in flight, do you have your controls set up for three engines? Is the autopilot interfering with engine settings? Low power on the right engine would give the symptoms you are experiencing.
5. Unless you are familiar with what the aerodynamic coefficients in the air file do you are unlikely to improve anything by experimenting.
6. There is nothing in the air file that you can change that biases lateral control to one side, the coefficients operate symmetrically.
7. My advice is to leave the air file alone. The fact that changing it for another seems to have improved your situation is very odd and unable to be supported by practical considerations.
8. Is the autopilot a .gau or an .xml gauge?


Resource contributor
Hey antaris,

Well I used aired to edit the air file as suggested by someone in another forum, to do the following:
---"Open your Airspeed Courier .air file and check for any entries with the word Autopilot in the title. I suspect there won't be any, but if there are, delete them. Leave the .air file open and then:
Open your default C172 .air file and do the same check. Hover your mouse over an 'autopilot' entry, right click and select Copy to Clipboard, then:
Go back to your open Airspeed Courier .air file, right click on any entry and select Add from Clipboard. Repeat for each 'autopilot' entry and then Save the Airspeed Courier .air file.
Along with your amended Aircraft.cfg file, this .air file should now give you a working Autopilot."---

I did this but got no changes; and I even copied section 516 "Aileron/Rudder Trim constants" (because the ini file referred to the aileron trim constant value as having implications in the autopilot heading hold) from both the C172 and another aircraft I have this AP working on, and both times still the same result :/



Resource contributor
Hey Roy,

If the fault is with the autopilot, then why is this the only aircraft that behaves erratically when I use this AP with it? :/
all others I've 'installed' this AP to work perfectly, and they all have an assortment of build configurations, number of engines, etc. Many are even by the same model designer as this Airspeed Courier!
And this AP doesn't touch the throttles or any other engine settings, just holds the current altitude and heading. (Also the Courier is a single engine aircraft).
I have no idea how to work with the coefficients in the air file...
I understand that changing the air file and it suddenly working may be odd, but thats exactly what happened, hence my conclusion that the error I'm experiencing is .air file related.
This autopilot is a xml gauge.



Roy Holmes

Resource contributor
As you found out though changing air file parameters and removing any autopilot references in the .air file does nothing.
The Courier engine/prop rotation direction is opposite to other non-UK airplanes. That should affect the yaw direction under power and with power off.
I doubt that this is addressed in a heading hold but it could account for the difference with .air file if the Courier air file had a strong yaw with power coefficient.


Resource contributor
I seriously doubt that what I'm experiencing might be due to prop/engine rotation, otherwise I'd see abnormal behavior with and without AP :/
It must be some setting regarding autopilot/trim in the air file...
Would you like me to paste the xml gauge here so you can see if you can spot anything that may cause such issue? I'm assuming of course you would be savvy on xml gauges, because I most certainly am not o_O

I suspect that the autopilot and air file are OK .

Looking at the original post it seems that the autopilot is not being fed a Heading .
When you click Heading Hold on , the autopilot usually takes the Heading set by a Heading Bug in the HSI instrument and turns and flies the
Heading Bug Heading value .
If the autopilot is unable to get a Heading value then , the autopilot Heading Hold will never work .

The autopilot has to obtain a Heading value from somewhere ! !

I suggest you test by temporarily adding a HSI instrument that has a Heading Bug , and see if that works .



Resource contributor

The thing is that this autopilot's heading mode is actually more of a wing level hold function. The only heading input it gets is the heading the airplane is flying the moment I toggle the Heading mode on the AP, or at least thats how it's supposed to work (and how it does work in all the other aircraft I added this AP to).

I have had the experience in the past of adding an AP to an airplane that had a HDG mode that needed a functional HSI with a heading bug, and not having such HSI, as I selected HDG mode the aircraft would simply keep flying as it was, with the ailerons fully free for me to bank (as if there was no AP mode engaged whatsoever).

Since the situation here is the exact opposite, the airplane just banks right endlessly, I assume it's an incorrect configuration of something in the air file, or an interference of what the xml AP gauge 'needs' and what the aircraft.cfg or air file can provide :confused:

I'm really not convinced that the air file has nothing to do with it, since if it didn't, then why does the AP work if I simply assign a different air file (one from another airplane that has this AP working for example) to the relevant aircraft? 0.o

Any more insights and help would be greatly appreciated!


Roy Holmes

Resource contributor
I downloaded the Courier and installed it in FSXA.
I substituted the Trimotor autopilot control for the altimeter in the Courier and assigned two keys to autopilot Heading INC and DEC.
The as issued Courier aircraft.cfg has autopilot_available =0. With that setting the added autopilot gauge was of course inop.
I changed the setting to 1 and the autopilot heading hold worked. Heading DEC would turn it left and heading INC would turn it right.
If the heading control was continuously selected the airplane would overbank in either direction as described.
The reason is quite simple, the autopilot entry in aircraft.cfg should have a max_bank= entry. I put this in and used max_bank=25.
With that setting the bank is limited and the airplane turns as it should.

So the issue was in the autopilot as I said in my first post.


Resource contributor
Hey roy,

So let me see if I understood this properly, to make it work you did:
1. Installed the Airspeed Courier and that Ford trimotor update i linked in my first post
2. added the AP gauge that came with that trimotor update to the courier's panel
3. used hdg inc and hdg dec to make the aircraft turn where desired
4. entered max_bank=25.00 in the aircraft.cfg

This it?

Because i just checked and I have max_bank=25.000 in my courier's cfg, and clicking hdg inc or heading dec doesn't do anything! It still banks on and on to the right if HDG hold is selected :(
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Resource contributor
I just noticed something that might be the cause of my problem...

The message "your heading indicator is set incorrectly" keeps popping up. And even if I click the assigned key to set it correctly, the message just keeps on appearing.
Could the Heading indicator be messed up, and in turn be messing up the heading cmd of the AP? And if so how can I fix this since the sim appears to ignore me when I click the 'heading indicator (reset)' key?

I never got this message in any of the other aircraft where I have successfully installed and used this AP gauge!