Autopilot with APR armed does not capture localizer

[gyroblau]

Hello from Germany,

I am flying the Black Square TBM 850 with GTN 750 from TDS GTNXi Pro in FS2024.

With the ILS 25 approach loaded from EDDS (Stuttgart/Germany) I am flying towards the waypoint CI25 (before FAF UNSER) in heading mode with the approach armed.
ILS frequency ( 109.9 ISTW) is active in NAV1.

See picture 1 before reaching the extended centerline of RWY 25.
(Remark: The APR button of the autopilot was pressed shortly after this screenshot, so please see this picture as if the APR button would be armed already).

   

The problem is, that the aircraft passes the extended centerline without capturing the glideslope (see picture 2).

   

Sometimes, it works and it captures localizer and glidepath, and sometimes not?

Any idea, what is going wrong?

Thanks a lot!

Carsten

[adminOwner2]

Hello Carsten,

When the GTNX is in VLOC mode, all autopilot control is passed to the MSFS autopilot, the TDS GTNXi Pro does not have any input into this.

We suggest first capturing the localizer, either via the NAV function or via the APR function, only after this you can capture the glideslope. If this still fails, please ask for help from Blacksquare.

From the TDS end, you can search in our Discord for official information on the custom autopilot progress.

[gyroblau]

Sorry, there was a mistake in my first thread:
The problem is, that the aircraft passes the extended centerline without capturing the localizer (not glideslope).

As you can see in picture 1 and 2 in the HSI, the Nav1 source (ILS25) is recognized and the needle in the HSI is moving in, when approaching the extended centerline.
GTNXi is in LNAV VLOC mode.

But although APR mode is armed in the autopilot, the aircraft simply overshoots the centerline without capturing the localizer.

Your wrote:
"When the GTNX is in VLOC mode, all autopilot control is passed to the MSFS autopilot, the TDS GTNXi Pro does not have any input into this."

I don't understand, what you mean with this?

Isn't it right, that in real world the Garmin GPS is in charge for receiving ILS signal?

Can you please be so kind and explain in more detail:
What is probably going wrong here?
Who is in charge of capturing the localizer and switch from heading mode to approach mode?

And - what is meant by
"From the TDS end, you can search in our Discord for official information on the custom autopilot progress."
Does that mean, you are currently developing an autopilot for the SIM by yourself?

Thanks a lot for you help!!

[adminOwner2]

Hello,

In the context of the autopilot in general, it is true, the GTN Xi is a NAV receiver, but the NAV signal is being sent to the autopilot and the autopilot itself handles the LOC/GS, not the GPS unit. This is why we have a VLOC/GPS switch in GPS units.


In the context of MSFS, the TDS GTNXi respects the MSFS SDK by driving thee autopilot only in GPS mode. This means that in VLOC mode, it is entirely MSFS which handles the LOC intercept.

We would recommend a new test, using the same scenario, but at a lower altitude.

Yes, we are researching a new autopilot system, as it seems that such issues by respecting the MSFS SDK will not be fixed from the simulator side.