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NAV key and GTN 750 (almost works)

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While trying to get my JS41 follow Flight1's GTN 750 without any luck, I noticed that with GTN set for heading hold steering mode (through config file), with JS41 in V/L VOR1 mode, if you keep pressing NAV button on autopilot panel continuously (several times per second), aircraft will follow the track from GTN !, albeit EHSI will not show CDI needle, etc, but it doesn't matter. The problem is that this NAV button is not default and pressing NAV1 button from default control assignments will not do the same trick.

Has anyone got an idea how to somehow determine this custom NAV button and bind it for continuous engagement (through Fsuipc, etc.)?


PS. What is also interesting that JS41 follows KLN-90B from this developer ( ), it has override function for heading hold. Aircraft follows KLN perfectly, so I guess GTN could do too. 


Thank you.

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disclaimer: I am a novice programmer...I followed the suggestions given by the article on how to write a Lua script from "Guide to couple JS41 autopilot and Flight 1 GTN 750" I was able to figure out with microsoft visual basic to write the Script

while 1 == 1 do

ipc.writeLvar("L:FdModese1NavSwitch", 1)





I followed the instructions from the article and was able to implement the procedure which works...However, after about 25 minutes from the point of setting autopilot which engaged GTN750, I got the following error...

"An unhanded win32 exception occurred in fsx.exe [6828] then "new instance of visual studio community 2017 open up and I will place the debug file below so that maybe somebody with programming experience with visual studio will state what is going on....I am not sure if this is due to a memory error or a problem with Simconnect...

'fsx.exe' (Win32): Unloaded 'C:\fsx\PMDG\dlls\PMDGOptions.dll'
'fsx.exe' (Win32): Loaded 'C:\fsx\PMDG\dlls\PMDGOptions.dll'. Module was built without symbols.
'fsx.exe' (Win32): Loaded 'C:\fsx\PMDG_SimConnect_Ldr.dll'. Module was built without symbols.
'fsx.exe' (Win32): Loaded 'C:\Windows\winsxs\x86_microsoft.vc90.mfc_1fc8b3b9a1e18e3b_9.0.30729.6161_none_4bf7e3e2bf9ada4c\mfc90.dll'. Cannot find or open the PDB file.
Exception thrown at 0x12F419AF (PMDG_SimConnect_Ldr.dll) in fsx.exe: 0xC0000005: Access violation writing location 0x00000000.

Thanks in advance for suggestions. 

Bob Adams

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found the problem...stated above...the Lua script had some mistakes, corrected those mistakes and the GTN-750 and pmdg JS4100 will now talk to each other...

So disregard the former post of mine...


Bob Adams


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