PMDG 737 AutoThrottle and Couatl Running at KIAH in MSFS 2024

[EuroTexan]

There is some sort of a bug going on between Couatl and the newly release PMDG 738 that occurs at KIAH. Symptoms are frequent A/T disconnects on takeoff from KIAH runways and in the climb. This issue resolves if Couatl services are not running, and has been tested by multiple users. Any thoughts on this issue?

[EuroTexan]

These are the steps to recreate.

1. Start a flight in MSFS 2024 in PMDG 738 with Couatl running.
2. Populate any flight plan departing any runway at KIAH. For most test I selected 15L or 9.
3. Execute a departure with A/T engaged.
4. You will find the A/T disconnections occur sometime just before V1, sometimes at Vr and will continue until you are at the altitude when the GSX services are turned off.

Run the same test with Couatl disabled and turned off, and you will find there are no disconnections or EEC type engine issues and the flight is normal.

It is easily replicated and repeated. The behavior occurs even without any flight hardware connected. Looking forward to seeing the root cause and update.

[virtuali]

I tested it now, and I cannot reproduce it, see the video:

Are you using some app that interface/controls GSX ?

Maybe that one is causing it, so you are mislead thinking it's GSX (because it goes away when you close the couatl engine), but it just that, by closing the couatl engine would then stop that app to do whatever is doing in relation to GSX that might interfere with the airplane, maybe sending key events or setting LVars that were supposed to be received by GSX but are then passed to the airplane.

I can assure:

- GSX never tries to control the PMDG autopilot or any autopilot of any airplane.

- GSX only sends events to the FMC, following the PMDG SDK, and only when doing Payload or Refueling, surely not after takeoff or any other moment in flight.

- GSX will never WRITE to any custom PMDG LVar, it only reads those, and surely not after takeoff or at any other moment in flight.

[EuroTexan]

I do use P42 with the GSX add-on. Is there any way that could be a contributing factor? The odd thing is there are a couple of users that can reproduce it. Would you mind trying one last takeoff sequence on 15L with the takeoff performance page calculated and a TO-1 profile (with vspeeds populated) to see if you can see the event while Couatl is running. Also using the TOGA button to command the takeoff power with FD's active.

Thanks for checking, this is such an odd issue. I really appreciate your time.

[virtuali]

Would you mind trying one last takeoff sequence on 15L with the takeoff performance page calculated and a TO-1 profile (with vspeeds populated) to see if you can see the event while Couatl is running. Also using the TOGA button to command the takeoff power with FD's active.

Done that, no issues:

I saw the discussion on PMDG forum and, it seems that something in the KIAH area is causing TWO side effects:

- Engine spike in the 777

- A/T disconnect in the 737

About the 777 engines spike issue, I see PMDG suggesting to clear the WASM cache of the airplane, and TWO users (debbert and jmdriskell) who reported the problem was fixed after doing this, so it clearly not so simple as "GSX conflicts with PMDG at KIAH", since if it was a GSX problem, couldn't have possibly by fixed by clearing the PMDG WASM cache, it must be something else, like a conflict between a 3rd software, somebody mentioned Winwing (I AM running Winwing, but I don't have 737 hardware).

There is some custom code that runs at KIAH but, it only runs if you have FSDT KIAH installed, and the only thing it does, is to look in the Community folder to see if you have some AI traffic packs like AIG, FSLTL or FS Traffic, and it takes a couple of AI models from there and place them as static planes in the United hangar, it surely doesn't send any commands to the sim or the autopilot (nothing in GSX ever does that), and some users said it doesn't matter if you have FSDT KIAH installed or not, so it can't be that, since that code doesn't run if you don't have the FSDT scenery installed.

[EuroTexan]

Thanks Umberto. I have seen the EEC spike in the 737 so that wasn’t limited to only to the 777. I do have FSTL libraries installed for vpilot. The other user from the forum does not use FSDT IAH scenery, so it is not a likely candidate. I do have a lot of WinWing hardware, but was able to reproduce it with all that disconnected and unplugged. I even stripped all the controls down to a mouse only . The search continues!

[EuroTexan]

I decided to setup a debug and focused in on those FSTL objects. When I ran another test with everything running (Couatl, GSX, Hardware, SimAppPro) but canned the FSTL objects...bingo, the A/T disconnections resolved themselves entirely.

[EuroTexan]

Debug window showing the 2 FSTL objects running. I removed those and the A/T surge issues disappeared. Umberto, thanks again for helping me flush out this issue.

[virtuali]

Debug window showing the 2 FSTL objects running. I removed those and the A/T surge issues disappeared. Umberto, thanks again for helping me flush out this issue.

Thanks for your test. I tried replicating it as close as possible, I see the 2 AI planes and I flew circles around KIAH for 20 minutes, cannot replicate it.

I kept the same debug window opened (AP, Engines and Inputs) and I couldn't find any input being sent to either the throttles or the AP. The engines were just showing the usual normal smooth fluctuation when A/T is engaged, all normal.

Here's a small update you can try: it will spawn the 2 FSLTL (or any other AI), frozen on ground and with their simulation disabled, let me know if it makes any difference. The file should be placed here:

\Addon Manager\couatl\KIAH2

replacing the file with the same name there. Then restart the Couatl engine to make it active.

[EuroTexan]

Thank Umberto this worked, placing the file and running all products (GSX, SimApp Pro, AAO, FSLTL models in community) I have no further disconnection on 15L at KIAH and no engine surges.

[virtuali]

Thank Umberto this worked, placing the file and running all products (GSX, SimApp Pro, AAO, FSLTL models in community) I have no further disconnection on 15L at KIAH and no engine surges.

That's very good to hear, and it's really puzzling and sounds like a possible MSFS bug, since it seems placing an AI model with its own simulation enabled, has some effect on the user airplane. Now, GSX doesn't really need to place it active, so we fixed it in a very easy way (it was supposed to be a static plane after all) but, I wonder what might happen with other AI injectors that would generate dozens of AIs, all active.

[EuroTexan]

I flew a solid and turbulent IMC flight tonight KIAH - KAUS in BATC with moderate AI traffic injection on the ground and in the air. I used the new .PYE you provided today with zero issues, everything was perfect. After landing, I closed the sim and rolled back the .PYE file provided to the previous release and setup the same flight KIAH - KAUS. The A/T disconnected very quickly prior to V1 and the engine surging started again. I think we have a solid case here, although the technical explanation of why will perhaps take more time from the team at PMDG.

[mjchernis]

I just had this same issue today at ImagineSim's KDFW with the PMDG 737-800 using FS2024.   Happens at different airports as well but easily about 1/3 of the time now.   Also using GSX, SimApp Pro, AAO, with BATC injecting AIG models.

Honestly, had not dawned on me that it might have anything to do with GSX but I'll certainly try disabling it before the roll to see if makes any difference.