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GFC500 Approach Roll Steer setting
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by9468840 View Drop Down
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    Posted: 18 Dec 2021 at 12:12pm
Hi

I have a dual G5, GFC500 and IFD540 setup. 
I picked up the plane about a week ago after the GFC500 installation. 
So far everything works great except LPV approaches. ILS works great. 

I noticed today that when I loaded the LPV, I could not arm the APR mode on GFC500. 
It remained in HDG and ALT mode. I did see however megenta vertical and horizontal guidence on G5. 
I just could not engage APR mode on the autopilot.

I am quite confused about the "Approach roll steer" setting in IFD. Some say it needs to be DISABLED some say ENABLED. Mine is set to DISABLED at the moment. What exactly it should be set to? 
Could this config be the reason why I could not engage APR in LPV?

Baris 


Edited by by9468840 - 18 Dec 2021 at 12:13pm
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PA23 View Drop Down
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You probably want "Approach Roll Steer" enabled.  The setting allows the GPS to continue to send out "steering commands" to the autopilot in approach mode instead of the simple left/right of a CDI needle.

In my case with it disabled I lost GPS Steering on my autopilot as soon as the IFD switched to LPV (or VLOC) on the approach.  With GPS Roll Steering enabled I was able to use the Steering mode from the GPS to track the inbound course. 

Steering mode if I understand correctly, the GPS will look at the desired ground track and the current ground track and tell your Autopilot which way to turn to keep them aligned, kinda like being in heading mode and moving the heading bug back and forth to maintain a specific ground track.  If you don't have GPS Steering you are relying on the left right indication of a CDI (Autopilots monitor the same CDI output as the VOR indicator) and will slowly adjust their left right in response to the CDI needle and wind correction.
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kzimmerm View Drop Down
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Originally posted by by9468840 by9468840 wrote:

Hi

I have a dual G5, GFC500 and IFD540 setup. 
I picked up the plane about a week ago after the GFC500 installation. 
So far everything works great except LPV approaches. ILS works great. 

I noticed today that when I loaded the LPV, I could not arm the APR mode on GFC500. 
It remained in HDG and ALT mode. I did see however megenta vertical and horizontal guidence on G5. 
I just could not engage APR mode on the autopilot.

I am quite confused about the "Approach roll steer" setting in IFD. Some say it needs to be DISABLED some say ENABLED. Mine is set to DISABLED at the moment. What exactly it should be set to? 
Could this config be the reason why I could not engage APR in LPV?

Baris 

Hi I have the same equipment setup and can confrim that if you dissable rool steer you will not be able to arm app mode. I had tried this to deal with a 1-2 dot offest error on LPV approaches on last 1000ft AGL.  Good luck. kz  
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by9468840 View Drop Down
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Points: 9 		Post Options Post Options   Thanks (0) Thanks(0)   Quote by9468840 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Dec 2021 at 9:43am
yes I verified that when that setting is disabled it is impossible to arm a GPS approach. 
I have not yet tried an LPV approach. Does it really always fly it 1 dot or so off the centerline? 
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Gring View Drop Down
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Points: 737 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Gring Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 2021 at 7:27am
mine does not fly off center, however with a strong crosswind it is not as solid as other autopilots and will wander slightly.  I do think there is work to be done on the Avidyne navigator to improve this.
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dmtidler View Drop Down
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Points: 617 		Post Options Post Options   Thanks (0) Thanks(0)   Quote dmtidler Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 2021 at 4:24pm
Originally posted by Gring Gring wrote:

mine does not fly off center, however with a strong crosswind it is not as solid as other autopilots and will wander slightly.

This has been my general experience as well.
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chflyer View Drop Down
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Points: 1034 		Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 28 Dec 2021 at 7:16am
Originally posted by Gring Gring wrote:

mine does not fly off center, however with a strong crosswind it is not as solid as other autopilots and will wander slightly.  I do think there is work to be done on the Avidyne navigator to improve this.

That‘s an interesting comment. Given the GFC500 being the only modern digital full (VHF&GPS) a/p for PA28/C172 class aircraft, it would seem to be in Avidyne‘s interest to make this combo work well. Otherwise it is just another argument for a GTN over an IFD.
Vince
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Gring View Drop Down
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Points: 737 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Gring Quote  Post ReplyReply Direct Link To This Post Posted: 28 Dec 2021 at 8:31pm
let me qualify my statement.  Sometimes I think it flies rock solid, and other times I’m not sure. I flew an approach into KPGD tonight and it was on center and flew rock solid.  However, there was no wind to speak of.  I have had other times where there was a 40kt direct crosswind and it tended to wander.  That was with several earlier versions of the G5 software.
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by9468840 View Drop Down
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I did my first fully autopilot flown LPV approach yesterday. 
With approach roll steering enabled, it flew down to minimums with horizontal deviation stayed between 0-100feet along the whole approach. It was a windy day with 30 knots from the left. So I am very satisfified with the performance. 
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compasst View Drop Down
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Having  flown several aircraft with GFC 500 and various navigators (Avidyne 540 in my Cardinal and several models of Garmin stuff in other aircraft) I have observed in all cases that rudder trim (whether it is by foot or by trim wheel) can/will cause constant course deviation off the magenta/green line. It doesn’t take much improper rudder position to cause this off-course condition. Keep the ball centered and the GFC will keep the aircraft centered on the course line. This is much more evident close in on approaches than further out or on enroute courses.

It took me a while to figure this out, but you can readily confirm by using intentional gentle left rudder pressure for a minute or so, then right rudder pressure and note the commensurate course deviation that is caused since the GFC is trying to fly the poorly yaw trimmed aircraft straight.

I have flown one GFC with yaw damp and didn’t see any deviation issues.
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by9468840 View Drop Down
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I second this! 
I went for 6 LPV approaches yesterday. Dampening out the descend yaw with slight left rudder helped GFC500 nail the approaches dead on centerline. I don't know why the deviation is much more aggressive in LPV compared to ILS but with the ball coordinated, IFD/GFC500 flies the ILS/LPC approaches extremely well. 
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compasst View Drop Down
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I just finished a long call with tech support in which I detailed the issue of not tracking needle centered. I also documented my testing and findings for them to investigate independently of my work. Needless to say, they are glad to look into this as Avidyne is being blamed for this issue when it might have nothing to do with the electronic navigator, but rather with the human navigator.
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PA23 View Drop Down
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out of curiosity what are you using to display the course line?  eg digital/mechanical HSI? mechanical VOR indicator?

Something you can try, put the IFD in configuration mode and on one of the configuration pages there is the option to display/hide the to/from flag and set the CDI needle centered and see what you are actually seeing.

-PA
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