HansMatthijssen

GTN750 not picking up GS on RNAV/LPV approach

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Since a week none of my planes pick up the glideslope on any RNAV/LPV approach using the GTN750.

It is probably either a fake-pilot error, or something is wrong in my setttings, but I cannot pinpoint the problem, so I'm asking my fellow simpilots for help.
I load and activate a LPV approach in the GTN750 (various fields and planes attempted, Carenado Baron with REP and F33A with REP mostly). I get to the IAF in NAV mode, the plane follows the horizontal path without any problems. I descend to the published intercept altitude and then arm APP mode on the autopilot. I see the G/S indicators moving down, but when the plane should start to descend to follow the G/S it just stays in ALT HOLD mode.

On one occasion the plane did start to descend when it should, but instead of following the G/S, it kept on pitching down eventually reacing 4000 ft/min vertical speed.

Does anyone have any idea what's wroing here?

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Hi,

Was this working fine prior the last week?

Which XPlane version are you running: the latest official release version, or the latest beta version?

Did it started to fail roughly around the time you'd have updated XPlane to the latest beta version?

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I am running the latest release version.

I wish i knew when it happened exactly. But my best guess it either started around the time I updated xPlane to the latest version, or when I updated the GTN750 to the latest version.

I know that a couple of weeks ago (i haven't been flying much due to crazyness at work) it worked just fine.

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This sounds like the latest XPlane version (which is a beta if I'm not mistaken) is maybe causing this then. Can you try reverting back to the latest official RELEASE version instead?

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I guess I wasn't clear :). I am running the latest release version of xPlane.

The problems started when I updated from the previous release version of xPlane to this one. Or maybe when I updated the GTN750 to the latest version, im not exactly sure.

But to eliminate the xPlane side, I will try to find time to do a flight this week using the xPlane Garmin unit to see if I have the same problems there. I'll keep you posted!

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So, yesterday I took my Airfoillabs C172 out of the hangar and flew a LPV approach using the default Garmin unit in the plane. This time the glideslope was picked up perfectly. So it seems my problem is indeed somehow related to the Reality XP unit.

As soon as I have the time, I will fly exactly the same approach in the same Airfoillabs C172 using the GTN750 to see what will happen there (I'm expexting my plane to stay in ALT HOLD mode which is the problem I've seen lately and described above).

Once I've done that testflight, I'll edit this post with my findings.

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Repeated the same flight with the same plane and same approach. This time using the GTN750 though. When I enabled it, xPlane immediately crashed to desktop (I get that almost every time i enable or disable the GTN unit).

Second attempt I could swtich it on though and I tried the approach. Again the autopilot just stayed in Altitude Hold mode, the plane did not start a descent to follow the glideslope.

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The issue is not from the GTN. I've done several RNAV LPV approaches today and everything worked nice ^^

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xPlane version 11.21r2

I guess I'll have to open another topic asking how the <bleep> this got installed as I do not have the option to use beta's checked. Also I have no idea how to roll back. I guess this might be an opportune moment to just reinstall everything.

Sorry for causing this trouble, I really thought I was on the latest release version.

 

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11.21 should've fine though otherwise I'd guess there would be much more similar reports in the forum. Otherwise, you might want to search for conflicting plugins, starting with moving out all plugins to a different folder, testing if this cures the issue, then reintroducing the plugins one by one until finding the culprit.

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Ok, so 11.21 is the latest (I really got confused for a moment haha).

I already disabled xEnviro1.9 as I saw other problems reported with that plugin. I don't have a lot of them, so that is another test I will do. If all fails, I will just reinstall xPlane with Realty XP as the only plugin.

Don't get me wrong, I love the GTN750 unit! 😃

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Hi, have you made progress on the re installation?

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Due to very busy times at work and the extreme temperatures across Europe, it took way longer than expected.

I have now reinstalled X-Plane with only 1 plugin (that I cannot live without), X-Camera. I have the Airfoillabs C172, the Carenado Baron B58 with REP and the Carenado Bonanza F33A with REP installed. Also removed the complete Reality XP installation and reinstalled that.

Performing my first test flights right now. The GTN750 does not show up in the F33A virtual cockpit (I understood that is an officially supported feature?) and I cannot find how I fixed that last time. When I have figured that out (could take some time with above 30C temperatures here) I will be trying the LNAV approaches again.

 

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Got the GTN750 working in the Bonanza F33A using a .ini file from the forums here.

First test flight done. Appproach loaded and activated in the GTN750, AP on, APP mode selected. The plane turns perfectly to intercept the lateral path to the runway. I see the G/S indicators moving on the HSI. The plane however does not start to descend, it just remains in ALT HOLD mode.

I am starting to think that either I have some setting wrong, or I am doing something wrong (although it has worked before).

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Second test flight, same result. The plane does not pick up the G/S.

Approach selected and activated in the GTN750. Speed 90 knots, flaps down 1 notch, gear down, APP mode active, ALT HOLD at published altitude, LPV indicated on the GTN750 screen.

I see the G/S indicators moving down on the HSI, but the plane does not react to them and just remains in ALT HOLD mode.

This is a new and fresh install of X-Plane, all aircraft and the GTN units. Downloaded all the latest installers. The only plugin that is active is X-Camera, I assume I am not the only one using X-Camera and the GTN unit.

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I'm not familiar with this aircraft, but have you armed a vertical mode while still below the G/S? Otherwise I'd think the A/P wouldn't know you'd like to capture the vertical slope?

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The airplane is the Carenado F33A BONANZA  which according to the Carenado website has "Support for RealityXP's GTN750* (integrated into 3D cockpit, when available)."

I intercept the G/S from below indeed in ALT HOLD mode with APP mode active. The autopliot should then pick up the glideslope and announce GS mode when it does. I have just tested this in the same airplane with the RealityXP  GTN750 switched off (which means using the default X-Plane GNS unit) and that works perfectly just as described above.
WIth the GTN750 enabled however the G/S is not picked up, the airplane just stays in ALT HOLD mode

I have also noticed that even while the RXP GTN750 unit is tied to the Master Avionics bus, it will not switch off when i switch off the Master Avionics after landing/parking.

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I'd guess we would need other customers reporting a similar issue, or not, to find out what this could be. I'd guess should this be a GTN issue only, there would have been more reports and with more different aircraft.

This kind of problem might be related to something else in the Carenado aircraft 'enforcing' the A/P to work a certain way, effectively disabling our 'override'.

Nevertheless, the issue could be more recently due to the latest X-Plane updates?!? The way our A/P system work is very simple: if there is a lateral mode armed or engaged, it drives the F/D lateral. if there is a vertical mode engaged (in fact GLIDE_ON - i.e. 2048 in the X-Plane autopilot state datarefs), it also drives the F/D vertical. Furthermore, if a lateral mode is armed only, and there is a LCDI signal below 95% deflection, it automatically engages autopilot lateral mode.

Which leads me to think something in X-Plane, or with this aircraft, is no longer making the A/P see our GTN LCDI/VCDI signal as valid, therefore, it is not engaging the vertical mode but leave it armed only.

Are you sure the X-Plane HSI is connected to GPS and not to NAV1 or NAV2?

You can cross check the "sim/cockpit2/radios/actuators/HSI_source_select_pilot" for this (0: nav1, 1: nav2, 2: GPS).

Also can you please cross check "sim/operation/override/override_gps" and see if it is 1?

 

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Posted (edited)

The only thing i could think of is the one addon that is stil running, which is X-Camera. For a test flight I can try to switch it off.
Also the GTN was not integrated by default in de Carenado Bonanza, I had to download an .ini file from to forums here to make that work. I assume the ini file is just to make it visible and cannot mess with the way the GTN actually works.

I have not tested this in my current setup after re-install because I really want to keep it as minimalistic as possible for the tests, but before re-install this same problem occured in any aircraft that I used the GTN unit in. Meaning this Carenado Bonanza F33A, but also the Baron B58 from Carenado.
Now thinking of that, I do/did have the Simcoders Reality Expansion Pack installed for both these aircraft. Could that be a problem? (Although I am pretty sure I'm not the only one using this combination, the REP brings so much extra to the Carenado aircraft).

Ill be doing another test flight this week and will let you know about the datarefs you asked me about. How do I check the values for these?

As always thanks for the answer/help Jean-Luc.

Edited by HansMatthijssen

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I'm looking forward your feedback but I wouldn't be surprised REP is 'playing' with the A/P as well.

Besides, when I mention the Baron I mean the default Baron 58 included in the simulator, not any third party aircraft, just to cross check the issue is inherent to the GTN or the a combination of third party plugins.

As for checking the datarefs:
Plugins | Data Ref Editor | Show Data Refs

It should be installed standard with XP11 AFAIK, otherwise
https://developer.x-plane.com/tools/datarefeditor/

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Posted (edited)

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I found that dataref editor. Values seem to be what they should be.

Edited by HansMatthijssen

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What about deactivating 'connect GPS to VOR indicator' ?

Also just in case it affects the operation, what about enabling 'Use Audio Panel' ?

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I cannot enable the Audio Panel. I think that is because in the VC the GTN is placed over the top of the default Audio Panel and the GNS430 default unit.

I dont have time for test flight now, but will check later with the "connect GPS to VOR indicator" unchacked.

Would be nice to see the GTN settings of someone that does not experience any problems.

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Even though you won't have access to the audio panel because it is masked/hidden, I'd suggest you enable the option to cross check if this has an effect internally in the trainer regarding the issue you are reporting.

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