RNAV approach with GTN 750 and vector off track

[Karelpatch 29]

Hi,

I’m having some trouble understanding what I did wrong:

I was flying under heavy fog to KTHV with my A2A Bonanza and brand new Reality XP GTN 750 and I loaded a vector approach to RW 17. 

As I reached the initial fix, I put my AP in approach mode. The plane aligned to the 166 degrees vector, the CDI was showing a nice full arrow and when I reached the FAF the AP catched the glideslope and started the descent. 

But from that moment, I watched the TRK moving away from the 166 DTK by a few degrees as we were approaching. At runway level, the track was at 171 degrees, leaving the runway to my left. 

What could have caused the plane to move away from the vector track? It was supposed to track the vector since it even did catch the glide slope. I searched in every manual, wondering if this had something to do with the HDG knob for instance, but I don’t think so. Or maybe it does?

Weather was overcast from 300ft and no wind.

 

Thanks for your tips!

[FPStewy 538]

I'll give this a try, was it FSX/P3D/XP ?

[FPStewy 538]

I just did this but with the F1 GTN and it was perfect.

[Karelpatch 29]

1 hour ago, FPStewy said:

I just did this but with the F1 GTN and it was perfect.

I’m on P3D. Didn’t retry it yet. What is your process to make a vector approach?

[FPStewy 538]

 

9 minutes ago, Karelpatch said:

I’m on P3D. Didn’t retry it yet. What is your process to make a vector approach?

KLNS - V143 SUEDE via ETUVY RNAV R17 - KTHV

[Karelpatch 29]

1 hour ago, FPStewy said:

 

KLNS - V143 SUEDE via ETUVY RNAV R17 - KTHV

Sorry, I meant what are the steps with the GTN and autopilot? Where do you go into nav mode and then approach mode, and so on?

I’m wondering if I did everything right or if these kind of RNAV and autopilot errors are common. 

[fppilot 4,339]

1 hour ago, Karelpatch said:

Sorry, I meant what are the steps with the GTN and autopilot? Where do you go into nav mode and then approach mode, and so on?

I’m wondering if I did everything right or if these kind of RNAV and autopilot errors are common. 

How do you have the RXP GTN configured?  What selections?  To enter the Configuration menu do a shift+right-click on the top edge of the RXP GTN's bezel.  If that does not bring up the menu, then bring up the RXP GTN popup and then shift+right-click on the popups top bezel edge.  Make a note of what settings are enabled, particularly in the top section. But also check and report the settings in the Advanced section. Scroll to find it, and then make sure  you click its arrow to expand it.

[Karelpatch 29]

2 hours ago, fppilot said:

How do you have the RXP GTN configured?  What selections?  To enter the Configuration menu do a shift+right-click on the top edge of the RXP GTN's bezel.  If that does not bring up the menu, then bring up the RXP GTN popup and then shift+right-click on the popups top bezel edge.  Make a note of what settings are enabled, particularly in the top section. But also check and report the settings in the Advanced section. Scroll to find it, and then make sure  you click its arrow to expand it.

And I didn’t even know about these options! 

Here are my settings (didn’t touch anything yet):

https://imgur.com/gallery/pIxdvEK

[Karelpatch 29]

Some relevant screen grabs of the track:

https://imgur.com/gallery/b294ijK

First picture, I am on 166 vector.

Second one: I have reached FAF and slowly going off track (171 degrees on the picture.) The leg was activated with the countdown confirming 166 degrees. 

Edited January 20, 2019 by Karelpatch

[fppilot 4,339]

4 hours ago, Karelpatch said:

And I didn’t even know about these options! 

Here are my settings (didn’t touch anything yet):

Reading the documentation is a great place to start with a new product.  The settings can and do vary by aircraft as not all aircraft developers follow standard or consistent conventions.  I do not have the A2A V35 Bonanza.  Perhaps someone else can confirm the settings they use in the V35. 

What I use for the A2A Cessna 182 is this.  I will state these by position rather than typing the names.  Under Panel Instruments try selecting the 1st, 2nd, 3rd, 5th, and 7th options.  Then scroll down and find the Advanced Options section.  Open that tab up and find the entry that reads something like Use Simulator GPS Commands and select it.  Then fly the V35 and see if those wake up the function you are looking for.

Make sure that when using the GPS to track an approach that you have the CDI selector on the GPS set to GPS, not to VLOC.  Look around the panel of the V35 for a separate GPS/NAV switch in case that is an issue.

Hope that helps.  If not, play around with the selections. 

Edited January 21, 2019 by fppilot

[Karelpatch 29]

Will check. Thanks 

[FPStewy 538]

On 1/20/2019 at 12:52 PM, Karelpatch said:

Sorry, I meant what are the steps with the GTN and autopilot? Where do you go into nav mode and then approach mode, and so on?

I’m wondering if I did everything right or if these kind of RNAV and autopilot errors are common. 

I find that RNAV's can be tricky but as long as you are at the right speed and designated height everything is ok but I'm finding out that if you are just a tad off you can easily lose the GS and if I miss the RNAV I basically just do an ILS approach. When I see the GTN on LNAV my GS indicators come alive in the HSI and I just wait until the GS starts to move down and when the GS Indicator is one dot high then I engage the APR.

[RXP 2,336]

19 minutes ago, FPStewy said:

and when the GS Indicator is one dot high then I engage the APR. 

Hi, I know you are not using our product but so that it might helps our customers reading your answer:

Please note the genuine Reality XP GTN 750/650 Touch offers 'installation' settings (Aircraft Flight Manual Supplement - AFMS) and one of these is 'GPS Selected':

AUTO
When in GPS mode and whenever a GPS approach mode is active, no associated messages appear and no pilot action is required. The pilot is also allowed to select automatic or manual GPS to ILS CDI transitions on the System Setup page.

PROMPT
When in GPS mode and whenever a GPS approach mode is active and the pilot has enabled the A/P APR Outputs (an associated message is displayed telling the pilot to enable the A/ P APR Outputs). This setting will not allow the pilot to select automatic GPS to ILS CDI transitions on the System Setup page (only manual transitions are permitted). For Honeywell (Bendix/King) KFC 225 and KAP 140 autopilots. 

Because integration in our simulators isn't so constrained to what autopilot type/model is in use in the aircraft, our implementation simulates the 'pilots' point of view (but we do output the necessary signals so that any 3rd party A/P developer could really make the A/P work like a real one).

In short: you are in NAV mode + GPS Selected Auto: it will arm the A/P APPR mode for you, otherwise if GPS Selected Prompt: it will prompt you to arm the APPR manually.

[Adrian123 1,015]

When in Auto, even activates on a 3nm Visual approach selected. That was a pleasant surprise.

[Rene_Feijen 125]

I own the RXP 650 and 750. I wonder why I should even NOT connect the GPS to HSI etc? In another way: I see these options, by why do I select which one?